Cambrian and Ordovician:
Acoelomate: animals not having a true coelom (sponges corals, etc). A coelom is a fluid filled cavity that
forms the main body cavity of organisms. It is formed by the splitting of the mesoderm of triploblastic.
The coelom functions to separate the muscles of the body wall from the gut so the gut can move
independent of the body. It also provides an enlarged area for organs to be housed. Present in
arthropods, molluscs, annelid, echinodermata, vertebrates.
Algal Mats: a layer of algae on the benthic zone. Made by the accumulation of cyanobacteria and
sediments. This provided the large nutrient rich aquatic floor for the burrowing animals later in the
Amebocyte: animal cell that is present in the sponge. Its location is not fixed and has the ability to
transport nutrients to the pinacoderm from the choanocytes which absorb the food.
Archeocyte: The archeocytes form the eggs of sponge cells in female sponge. They differentiate from
the amebocytes. Basically they are ameobocytes that have become eggs. Ameobocytes receive the
sperm from the choanocytes and transport the sperm to the archeocyte.
Asymmetric body plan: a body plan that has no symmetry what so ever.
Bilateral symmetry: a body plan where the organism is symmetrical in only one plane. Therefore, it is
cephalized meaning it has an area where the sensory nerves are concentrated. This allows the organism
to be active instead of passive because it could now chase after things and runs away from things. This
body plan is associated with triploblasty because muscles allow for cephalisation. Directed motion.
Bivalve: a mollusc that has two shells hinged together. Ex clams, scallops, oysters, mussels.
Blastophore: a mouth like opening of the archenteron on the surface of the embryo in bilateral
organisms. If the blastophore becomes the mouth of the organism then we consider the organism to be
a protostome if the blastophore is the anus then the organism is considered a deuterostome.
Blastula: the stage of development of an animal embryo that results from the cleavage of the fertilized
egg. This looks like a hollow ball. After this the blastophore forms.
Bryozoa: tiny colonial animals that generally build stony skeletons of calcium carbonate, superficially
similar to coral. Have a well developed calcite skeleton. Contain ciliated tentacles and a coelom. Food is
collect by the tentacles which surround the mouth and are carried by the lophophore. They reproduce
by asexual budding.
Burgess shale fossils: 505 million years (Middle Cambrian) in age, making it one of the earliest fossil beds
to preserve the soft parts of animals. The pre-Cambrian fossil record of animals is sparse and
ambiguous. Rocky mountains of BC. Fossilized marine invertabrates, algae, sponges. This was evidence
of the Cambrian explosion. The fauna doesn’t exist now. Cambrian: began 542 million years ago and lasted like 54 million years. Great amount of organismal
diversity. Before the Ordovician and after the ediacaran.
Cambrian burrowers: worms which burrowed into the sediment, either actively catching prey or letting
it settle on its tongue. This was untapped resources on the marine floor because all the cyanobacteria
had sedimented and formed algal mats that were very nutritional.
Cambrian Explosion: a short interval of rapid intense increase in biodiversity that occurred in the early
to mid Cambrian period. This is based on the fact that many different fossils have been found of marine
multicellular organisms in the burgess shales and the chengjiang fossils. The problem is figuring out
whether this explosion is an apparent one due to the fact that we are missing the fossil record of the
previous organisms or whether the organisms evolved this fast. Did this also occur because of an
increase in calcium and silicon minerals that allowed the organisms to fossilize.
Cambrian Swimmers: swimming organisms in the Cambrian fauna.
Carnivores: organisms that eat other animals.
Cephalisation: is an evolutionary trend, whereby nervous tissue, over many generations, becomes
concentrated toward one end of an organism. This process eventually produces a head region with
sensory organs. This allows the organism to not be passive and to have directed motion.
Cephalopod: the most highly evolved members of the phylum molusca. They are predators and were
very fast allowing them to attack their prey. Modern members of the class are the squids and the octopi.
Have tentacles surrounding the head.
Choanocyte: cells that line the interior of Asconoid sponges that contain a central flagellum surrounded
by a collar of microvilli. It is the closest family member to the free-living ancestor called
choanoflagellate. The flagellae beat regularly, creating a water flow across the microvilli which can then
filter nutrients and other food from the water taken from the collar of the sponge. Food particles are
then phagocytosed by the cell. They differentiate into the sperm of the sponge and are released into the
Choanoderm: the layer choanocytes on the inner layer of the sponge (the osculum). There job was to
pump water with their flagella and filter it through their microvilli. They feed and send excess food
through to the amebocytes which take it to the pinacoderm of the sponge after they eat. This is
considered a division of labor.
Choanoflagellate: group of free-living unicellular and colonial flagellate eukaryotes considered to be the
closest living relatives of the animals. Had a cell body with a single flagella and a collar of microvilli. They
formed aggragates because they were able to pump more water as a group than the sum of each other
could do alone. They were filter feeders. Algae through the collar.
Cnidaria: aquatic invertabrates including the hydra, jelly fish and corals. Has a diploblastic body with the
two layers separated by the mesoglea. They show radial symmetry. The body cavity served as both a
mouth and anus. The opening is surrounded by tentacles. Exist as free swimming medusa and as sessile
polyps. Polyps can be colonial. Alternation of generations life cycle Cnidocyte: function in feeding and defence of the cnidaria. They are present in the mesoglea of the
cnidaria. The most common form is the nematocysts. These have barbed tips and contain toxins that
disable their prey.
Coelom formation: Forms via two mechanisms; Schizocoel and enterocoel. In schizocoel the mesoderm
forms at the junctions of the endoderm and ectoderm. The mesoderm slowly grows and the space
inside it is the coelom. In enterocoel the coelom is formed by the budding off from the archentron. Once
again the space contained in between the mesoderm cells is the coelom.
Coelomate: having a fluid filled space called the coelom. This is formed via two different mechanisms.
Schizocoel and enterocoel. The coelom is contained inside mesoderm tissue. The purpose of the coelom
is to allow for the movement of the archentron without the movement of the body. This obviously
occurred because of the presence of the mesoderm. Therefore, the mesoderm allowed for the coelom
to develop meaning that only triploblasts have coeloms.
Colonial choanoflagellate: The choanoflagellates are the organisms that had a collar of microvilli and a
flagellum that was used to pump water across the microvilli for filter feeding (algae). They became
colonial because there was an emergence property of a greater volume of water being pumped when
they aggregated. No division of labour and no communication; just colonial.
Corals: colonial cnidarians which compromise of colonies of individual polyps joined by living tissue,
many live within a calcium carbonate exoskeleton. These are the sessile stage of the cnidarians life cycle.
Large amount of biodiversity in the coral environment.
Deposit (substrate) feeders: swallows sediment to get to the microorganisms living inside. These were
the Cambrian burrowers. They fed by eating the sediments and releasing them through the anus and
absorbing the necessary nutrients. This was very good for the burrowers because it allowed them to tap
into the nutrient rich resource of algal mats.
Detritivores: soil animal like worms that extracts nutrients from detritus. Feed on dead and
Deuterostome: animals with a true coelom, radial cleavage of the blastula, and in which the anus forms
first (the blastophore becomes the anus), the coelom is formed by enterocoel. The three phyla are the
echinodermata, chordate and hemechordata.
Diploblastic: having only ectoderm and endoderm. The derm layers are separated by mesoglea. This can
be seen the cnidarians. This type of tissue construction has no mesoderm so the gut can’t move
independent to the organism’s body. This is considered to be the second type of eukaryote to evolve
after the sponge which had no tissues. Diploblasts are associated with radial symmetry and passive
organisms. The gut serves as a hydrostatic skeleton in which the organism uses to return to form after
the contraction of its muscles. The muscles are arranged longitudinally in the endodermis and circularly
in the epidermis. Ex, cnidarians.
Doushantuo Fossils: Doushantuo fossils are all marine, microscopic, and preserved to a great degree of
detail. The latter two characteristics mean that the structure of the organisms that made them can be
studied at the cellular level, and considerable insight has been gained into the embryonic and larval
stages of many early creatures. One contentious claim is that many of the fossils show signs of bilateral symmetry, a common feature in many modern-day animals which is usually assumed to have evolved
during the later Cambrian Explosion. They look like embryos.
Ectoderm: tissue that covers the body surfaces. It emerges first and forms from the outermost of the
germ layers. Generally speaking, the ectoderm differentiates to form the nervous system, epidermis.
Helps transport nutrients. The ectoderm is also what differentiates to form the endo (archenteron the
gut) and meso derms.
Ectoparasites: Parasites are classified based on a variety of aspects of their interactions with their hosts
and on their life cycles. Those that live inside the host are called endoparasites (e.g., hookworms) and
those that live on its surface are called ectoparasites (e.g., some mites).
Ediacaran Fossils: soft bodied animals possibly coelenterate, present in late Precambrian times, bear
little resemblance to older organisms. Could show that there was multicellular life before the Cambrian
Ediacaran period: immediately preceding the Cambrian Period of the Palaeozoic Era. Period where it is
believed that multicellular organisms might have existed.
End Ordovician Extinction: The Ordovician came to a close in a series of extinction events that, taken
together, comprise the second largest of the five major extinction events in Earth's history in terms of
percentage of genera that went extinct. The only larger one was the Permian-Triassic extinction event.
Endoderm: primary germ layer in the embryo of multicellular animals that gives rise to digestive tracts
etc. It is derived from the ectoderm and is present in both diploblasts and triploblasts. In cnidarians
contains the longitudinal contractile elements.
Endoparasites: parasites that live within a host organism. They physically enter the cell and replicate
within it. An example is plasmodium.
Enterocoel: the process by which the coelom forms in protostomes that undergo spiral cleavage. The
coelom forms by an outpocketing of the tissue at the junction of the ecto and endo derms and grows
into a cavity called the coelom.
Epidermis: The outer layer of skin on an organism. In the sponge it is pinacoderm. There are many types
Filter feeder: organisms that feed on food in water. They feed by letting water pass through their
filtering structure (ex. microvilli) and this allows the nutrients in the water to be absorbed by the
organism and digested. This feeding structure is present in sponges and bivalves.
Gastrodermis: the epithelial lining of the gut found in the nematode worms.
Gastropod: a class of molluscs. Ex snail. They secrete their shell from the mantle and coil their shells.
Gastrozooid: the name of the polyp when it is in a colony and feeding. Gastrula: the animal embryo once the germ layers have developed. This is after the blastula and occurs
when the archenteron opens inward to make the blastophore.
Gonozooid: the name of the polyp when it is in a colony and is going to become a medusa, therefore
release gametes to reproduce.
Herbivores: organisms that feed on plants. They are referred to as primary consumers. Have the ability
to digest the plant`s cell wall to obtain the nutrients inside.
Hermaphrodite: an organism that has both the male and female sex organs. This allows for greater
number of offspring to be produced by the species compared to if they only had one reproductive
structure. This way when two mates come together they always produce two offspring instead of one.
Self fertalization will not occur due to a mechanical inability and because of the loss of variation.
Organisms that don`t mate a lot are more likely to be hermaphrodites. Ex flat worm.
Homeotic genes: specify the anterior-posterior axis and segment identity during early development.
They are critical for the proper placement and number of embryonic segment structures (such as legs,
antennae and eyes). They help determine the location of structures on organisms but do not determine
the structure. They are universal so they can function and express themselves in different species.
Homeotic mutants: Incorrect expression of homeotic genes can lead to major changes in the
morphology of the individual. Like a second set of wings. Scientists can remove cells from different
organisms and place them in others to make mutants.
Hox genes: homeotic genes in the fruit fly. These genes code for location of structures within an
Hydrostatic skeleton: the skeletal system that used water to expand contracted contractile fibres. This
was the earliest type of skeleton present in the sponges.
Lophophore: a characteristic feeding organ possessed by three major groups of animals: the
Brachiopoda, Bryozoa, and Phoronida , described as a ring of ciliated tentacles surrounding the mouth,
but it is often horseshoe-shaped or coiled. The lophophore surrounds the mouth and is an upstream
collecting system for filter feeding. Its tentacles are hollow with extensions of a coelomic space thought
to be a mesocoel. The gut is U-shaped with the anterior mouth at the center of the lophophore. The
anus is also anterior, but is dorsal to the mouth, outside the ring of the lophophore.
Mass feeders: organisms that feed on solid food and use parts of their body make physical changes to
the food before ingesting it into the internal organs.
Medusa: a form of cnidarian in which the body is shortened on its principal axis and broadened,
sometimes greatly, in contrast with polyps. The motile stage of the cnidarians life cycle.
Mesoderm (formation): allows the formation of a coelom, which allows more room for independent
growth of the body organs and the coelomic fluid may also act to cushion and protect them from shocks.
Forms in two different manners; enterocoel and schizocoel. In schizocoel (associated with protostomes
and radial cleavage) the mesoderm originate at the junctions of the endo and exo derms. This means
that there will initially be two coeloms. In enterocoel (associated with spiral cleavage and deuterostomes) the mesoderm buds of the top of the endoderm layer (archenteron) and forms the
coelom this way. Mesoderm allowed the gut to move independent of the body. This also allowed for the
formation of muscles which allowed organisms to become non-passive which allowed them to dictate
there motion in an according manner to which they are able to go get resources.
Mesoglea: the fluid that is present between the endo and ectoderm of cnidarians. Acts as the
hydrostatic skeleton in cnidarians. Sort of like a mesoderm but is non-homologous with the mesoderm
Mollusc: are triploblasts, contain a coelom and are bilaterally symmetrical. Are soft bodied and their skin
is called a mantle. The mantle secretes CaCO3 and makes a shell on the surface of the organism. They
use a radula to eat food. The radula allowed them to scrape food off the ocean floor.
Omnivores: organisms that eat meat and plants. Secondary consumers.
Onychophora: velvet worms. Contain a segmented fleshy body. They digest their food by squirting out a
sticky substance to entangle their prey. Their fleshy legs allow them to move quietly they live in the dark
Ordovician period: lasting from 448 to 443 mya following the Cambrian and preceding the Silurian. Most
land part of the southerly Gondwana. Marine life composed of trilobites, brachiopods formative fish and
land plants might have invaded for the first time.
Pinacoderm: the outer layer of the sponge that is made of pinacocytes. This layer functions like an
epithelial layer for the sponge keeping things out of the organism.
Platyhelminthes: flat worms are hermaphrodites which is a new reproductive system. It feeds on
cnidarians and uses their cnidocytes to protect itself. There is a mechanical barrier to prevent self-
fertilization. Have a ciliated bottom that is used to locomote the organism and also contains filaments
and fibres to move in an acordian like fashion. Made themselves very flat to increase their surface area
to volume ratio. Acoelomate triploblastic bilateral symmetry. No anus. Diffusion of nutrients.
Polychaete: these are the annelid worms that are segmented. They have circular muscle in the outer
layer and the longitudinal muscle in the inner layer. They do have a coelom and are burrowers. They use
the achordian like motion to move.
Polyp: is one of two forms of individuals found in many species of cnidarians. The two are the polyp or
hydroid and the medusa. Polyps are approximately cylindrical, elongated on the axis of the body. The
aboral end is attached either to the substrate by means of a disc-like holdfast if the polyp is solitary, or is
connected to other polyps, either directly or indirectly, if the polyp is part of a colony. The oral end
bears the mouth, and is surrounded by a circle of tentacles. Can form a colony and feed and will be
called gasterozooids. When they specialize into medusa they are called gonozooids.
Porifera: primitive, sessile, mostly marine, water dwelling filter feeders that pump water through their
bodies to filter out particles of food matter. Sponges represent the simplest of animals. The phylum that
houses sponges. Therefore, asymmetrical and no tissue. Predators: organisms that are cephalized and bilateral and non-passive. They go attack their prey and
look for food don`t wait for it to come to them.
Protostome: all animals with a true coelom, spiral cleavage, and where the mouth forms first (molluscs
Pseudocoelomate: animal which has a fluid filled sack in between two layers as oppose to inside the
Radial cleavage: characteristic of the deuterostomes, which include some vertebrates and echinoderms,
in which the spindle axes are parallel or at right angles to the polar axis of the oocyte.
Radial symmetry: when an organism is symmetrical in more than one plane.
Radula: is a toothed, chitinous ribbon typically used for scraping, cutting and chewing food before it
enters the oesophagus. It is unique to the molluscs, and found in all clades except the bivalves.
Reefs: stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate. The
accumulation of skeletal material, broken and piled up by wave action and bioeroders, produces a
massive calcareous formation that supports the living corals and a great variety of other animal and
Schizocoel: the formation of the coelom when the coelom forms from two separate sources.
Seminal receptacle: a place where sperm is kept until the egg is ready to be fertilized.
Slush ball earth: snowball earth but with less freezing allowing for some organisms to survive through
the glaciations. Some places around the equator didn`t freeze.
Snowball earth: In the late Neoproterozoic (extending into the early Ediacaran period), the Earth
suffered massive glaciations in which most of its surface was covered by ice. This may have caused a
mass extinction, creating a genetic bottleneck; the resulting diversification may have given rise to the
Ediacara biota, which appears soon after the last "Snowball Earth" episode. However, the snowball
episodes occurred a long time before the start of the Cambrian, and it is hard to see how so much
diversity could have been caused by even a series of bottlenecks; the cold periods may even have
delayed the evolution of large size.
Spiculos: are made of calcium. The sponges were able to take dissolved calcium and build structures by
mineralizing it. However if the ocean is too deep then the pressure makes the calcium dissolve and the
spicules have to be made with silica (glass) to hold the sponge upright.
Spiral cleavage: the cleavage planes are oriented obliquely to the polar axis of the oocyte. At the third
cleavage the halves are oblique to the polar axis and typically produce an upper quartet of smaller cells
that come to be set between the furrows of the lower quartet. All groups showing spiral cleavage are
protostomia, such as annelids and molluscs.
Sponges: They are primitive, sessile, mostly marine, water dwelling filter feeders that pump water
through their bodies to filter out particles of food matter. Sponges represent the simplest of animals. They have no tissues and have contractile vacuoles. Pinacoderm on the outside, spicules are the skeletal
elements (made of calcium and silica), choanocytes on the inside, amebocytets in between.
Suspension feeder(filter feeder): animals that feed by straining suspended matter and food particles
from water, typically by passing the water over a specialized filtering structure. Some animals that use
this method of feeding are clams, krill, sponges, some fish and sharks, and baleen whales.
Transcription factors: a protein that binds to specific sequences of DNA and thereby controls the
transfer (or transcription) of genetic information from DNA to RNA. They are able to adjust the DNA
sequence to change what will be transcribed.
Triploblastic: three primary germ layers: the ectoderm, mesoderm, and endoderm. Bilaterally
symmetrical and cephalized.
Tube feet: the many small tubular projections found most famously on the ventral face of a starfish's
arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes
sea urchins, sand dollars and sea cucumbers and many other sea creatures. Tube feet function in
locomotion and feeding. The tube feet in a sea star are arranged in grooves along the arms. They
operate through hydraulic pressure. They are used to pass food to the ventral mouth at the center, and
can attach to surfaces. Tube feet allow these different types of animals to stick to the ocean floor and
move very slowly. Tube feet consist of two parts: ampulla and podia. Ampulla contains both circular
muscles and longitudinal muscle, whereas the podia contain the latter only. Thus the podia use suction
to attach to the substratum.
Water vascular system: It is the system that allows the starfish to locomote using the tube feet as
Microevolution Part One:
Allele: an alternative form of a gene, with slightly different DNA than the other alleles of its type. A
diploid organism carries two alleles for each locus, one on each homologous chromosome.
Allele frequency: a measure of the commonness of an allele in a population with respect to other alleles
of that gene. Abundance of the allele within a population.
Allopatric speciation: speciation that results from a physical separation (geographic isolation:
fragmentation or climate change) of a population of organisms. The physical barrier prevents gene flow
between the two now distinct populations. Therefore, any mutations that arise in one population now
can’t be shared with the other. This allows for the accumulation of genetic differences making
Allopolyploidy: polyploidy that result from the fertilization of gametes which had greater than n
chromosomes (that weren’t haploid). The fertilization can’t be self induced. Therefore, the organism
must be fertilized by another closely related organism to make the zygote. At least one gamete ends up
having more than n chromosomes because of mistakes during meiosis or mitosis. This is a deleterious mutation in animals but is beneficial in plants when the chromosomal content is even (ie 4n, 6n). If the
chromosomal content is odd then the chromosomes can’t pair into homologous sets so the hybrid isn’t
Autopolyploidy: polyploidy that results from the self-fertilization of gametes which have greater than n
chromosomes. This unusual number of chromosomes in the gametes, just like in alloployploidy, results
from a mistake in meiosis or mitosis during the formation of the germ cells. Once again, the
chromosomal content must be even for the offspring to survive.
Behavioural isolation: A type of pre-zygotic isolation mechanism that results from the different mating
behaviour exhibited by the different species. This is a pre-mating type of pre-zygotic isolation
Beneficial mutation: a mutation that provides an individual with the mutation a selective advantage
over the other individuals in the population. This mutation can be the result of a chromosomal or a point
Biological species: the definition used to determine what a species is and what isn’t considered a
species. States that a species is a population of individuals that has the ability to interbreed in its natural
habitat and produced fertile, viable offspring. The definition of a species works well when trying to
define organisms that breed sexually but doesn’t work too well when the organisms are asexual because
they do not interbreed. With this definition of species the bacteria and the archaea domains of life
would have no species. Also this species concept isn’t good for classifying fossils.
Bottleneck effect: a sudden decrease in population density with a resulting decrease in genetic
variability within the population. This causes a lot of the alleles in the population to be wiped out and
the population will probably have new allele frequencies. This is an example of genetic drift. It reduces
the variation in the population and causes some alleles that previously had very low frequencies to have
very high ones. The population that expands from the individuals that survived the bottleneck will now
have a different allele frequency than the original population.
Chromosomal inversion: is a chromosome rearrangement in which a segment of a chromosome is
reversed end to end. An inversion occurs when a single chromosome undergoes breakage and
rearrangement within itself at the same position. The chromosome is cut inverted and placed back in
the exact same place. This is a type of mutation; can be beneficial deleterious or neutral.
Chromosomal translocation: occurs when a segment of the chromosome is cut and re-inserted in a
different non-homologous chromosome at a different location. This is a type of mutation that can be
beneficial, harmful or neutral.
Crossing over: is the process by which two chromosomes pair up and exchange sections of their DNA.
This often occurs during prophase 1 of meiosis in a process called synapsis. Synapsis begins before the
synaptonemal complex develops, and is not completed until near the end of prophase 1. Crossing over
usually occurs when matching regions on matching chromosomes break and then reconnect to the
other chromosome. The result of this process is an exchange of genes. This is a source of variation in
sexually reproducing orgaisms. Deleterious mutation: a mutation that lowers the fitness of its carriers. Can occur through any of the
methods of mutation whether chromosomal or point.
Diploid: an organism having one pair of homologous chromosomes.
Directional selection: occurs when selection favours a single phenotype and therefore allele frequency
continuously shifts in one direction. Under directional selection, the advantageous allele will increase in
frequency independently of its dominance relative to other alleles (i.e. even if the advantageous allele is
recessive, it will eventually become fixed).
Disruptive selection: changes in population genetics that simultaneously favour individuals at both
extremes of the distribution. When disruptive selection operates, individuals at the extremes contribute
more offspring than those in the center, producing two peaks in the distribution of a particular trait. This
leads to the fixation of the alternative alleles in the population which will result in two divergent
phenotypic extremes within the population. This can lead to speciation.
Dominant allele: The allele that has the ability to fully express itself when present in either the
homozygous or heterozygous forms.
Ecological isolation: a type of pre-zygotic isolation mechanism that works because the habitats that the
different species live in do not allow for the species to interact with each other and mate to produce
offspring. This is one of many processes that can lead to speciation because the now separated
populations can’t exchange genes (gene flow doesn’t occur) meaning that the heritable mutations that
occur in the populations will not be shared and the populations will diverge and become different
Ecological Species: a population of organisms that live in different ecological niches which means that
they are different species. They eat, sleep and live in different areas is the determining factor to
determine whether the populations are different species.
Female choice: This is a type of sexual selection that occurs when the female decides to mate with males
that only have a certain phenotypic trait. This results in an increase in the allele frequency of the allele
that is responsible for that trait. An example is the long tail of the birds. This is the reason why males of
many species now can be seen to have many bright colors and unique structures that are metabolically
expensive but help them attract potential mates. The females use these unique structures on the male
to determine if the male is fit enough to mate with so that her offspring are viable. The females must
make a careful selection because they invest a lot of metabolic energy into producing offspring than the
Fitness: the extent to which an organism is will adapted to its environment. Also the measure of its
ability to leave viable offspring compared to others.
Fixation: occurs when an allele is present in either each individual of a population or none of them (ie.
The allele frequency reaches either 1 or 0)
Founder effect: genetic differences between an original population and an isolated population offshoot
due to alleles in the small number of founder members of the new population being unrepresentative of the alleles in the original population as a whole. This is a type of genetic drift. The new populations allele
frequency isn’t a proper representation of the parent populations allele frequency.
Frame Shift: a kind of mutation that causes a change in the translational reading frame as a result of
insertion or deletion, usually leads to no or a truncated gene product being produced as a result of a
premature termination codon in the reading frame. The produced protein is usually nonfuctional.
Gametic isolation: This is a type of pre-zygotic isolating mechanism that occurs when the gametes of the
different organisms aren’t able to combine to form a zygote. The inability of the gametes to combine
results from the incompatibility of the receptors present on the surface of the gametes. This means that
speciation has occurred between the two populations.
Gene duplication: the generation of additional copies of a gene during normal cellular processes such as
recombination. Some DNA is taken from one homologous chromosome and added to the other. The
mutation is most likely deleterious but is sometimes beneficial. For mammals, haemoglobin is a
molecule with a duplicated piece of DNA that the reptiles do not have.
Gene flow: the spread of particular alleles within a population and between populations resulting from
outbreeding. It ensures that population don’t diverge from one another and functions to pass on
mutations that occurred in one population to the next. It is also beneficial because it increases variation
within the population.
Gene pool: all the genes and their different alleles that are present within a given population of
Genetic drift: random changes in gene frequency in small isolated populations owing to factors other
than natural selection. Examples are the bottleneck effect and the founder effect. The allele frequency
in these populations does not reflect the original large population’s allele frequency because of the
reduction of the individuals in the population.
Genetic equilibrium: occurs when the allele frequencies of a given gene are kept constant from one
generation to the next. This occurs when all the hardy-weinburg assumptions are met. Therefore, the
population must be infinitely large, no sexual selection must occur (ie. Random mating), each organism
must have an equal chance to pass on its genes to the next generation (ie. No natural selection), there
must be no gene flow (ie. No new alleles introduced into the population) and no mutations must occur.
Genotype frequencies: this is the frequency of a given genotype in a given population. For a gene with
two alleles there are three possible genotypes; the homozygous dominant and recessive and the
heterozygous. These genotypic frequencies must add up to one.
Habitat (ecological) isolation: This is a type of pre-zygotic isolation that occurs when different species
can’t mate with each other because they live in different ecological habitats and don’t encounter each
other. When a population that is interbreeding is broken up by a geological barrier then they are
ecologically isolated. This will probably lead to speciation as gene flow will stop occurring.
Haploid: the chromosomal state in which there is only one set of chromosomes. Therefore, there are no
homologous. Hardy-Weinberg principle: the principle that helps us predict the genotypic phenotypic and allele
frequencies of the next generation of offspring assuming that certain criteria are met. There can’t be any
sexual selection (random mating), any mutations, the population must be large (no genetic drift), all the
organisms in the population must have an equal chance of passing on their genes (no natural selection)
and there can’t be gene flow (no new alleles being introduced into the population).
Heterozygote advantage: the case where the heterozygote for a given pair of alleles is of superior fitness
than either of the two homozygous forms. This can be seen in the sickle cell anaemia trait in areas that
have high numbers of the malaria disease. The heterozygous individuals have the ability to fight off the
malaria better because there red blood cells will sickle killing the malaria parasite and slowing its spread
within the body.
Heterozygous: The condition when the genotype at a given locus has different types of alleles for the
Homozygous: The condition when the genotype of an organism at a given locus has only one type of
allele coding for the trait.
Hybrid breakdown: this is a type of post-zygotic isolation where the hybrid that is formed is fit to survive
the environment but the F2 generation that is produced is not viable or isn’t fit. The F2 generation can
be produced either by the mating of two hybrids or by the hybrid and the original parent species.
Hybrid sterility: this post zygotic isolation occurs when the hybrid that is formed has zero fitness. It isn’t
able to produce offspring because it is sterile. This prevents gene flow between the populations and
enforces speciation in ring species.
Hybrid viability: this occurs when the hybrid that is produced is perfectly fit and is able to live and
reproduce in its environment. In ring species this can sometimes lend itself into creating a hybrid zone
where only the hybrid lives. However sometimes, the hybrid is even more fit than any of the parent
species and is able to out compete them and form one large species.
Hybrid zone: occurs when the hybrid formed from two different species or sub species, due to
overlapping geographical habitats, is fit to live in its environment and starts to carve out its ecological
niche. This hybrid will eventually reproduce and increase its numbers and take over an area of land to
live in and this land will be considered the hybrid zone. The hybrid must be different from the parent
species and then will act as a barrier between the two parental species restricting any further gene flow.
Hybridization: is the process of creating a new species by the mating of different species or sub species.
The hybrid formed can either be inviable, sterile or fit. The parent species must be genetically different
from each other.
Inbreeding: mating between related individuals. This results in an increase in homozygosity of the
genotypes. However, it does not alter the allele frequencies of the population.
Male competition: a type of intrasexual competition that males do between each other to be able to
mate with the female. There are three primary types; combat, sperm competition and infanticide.
Combat occurs when males physically fight each other to eliminate the other male from the picture so
that they can have exclusive rights to mating with a female. Sperm competition occurs when a male will remove the sperm of the previous male that mated with the female and then will inject his sperm into
the female. He will then stay to make sure that the female doesn’t mate with another male that will
reduce the chances that his sperm will fertilize the egg. Finally, infanticide occurs when the male kills all
the offspring that were produced from a different male so that the female can stop nursing her cubs and
start her reproductive cycle again. This allows him to mate with the female and pass on his genes.
Mechanical isolation: a type of pre-zygotic isolation mechanism that doesn’t allow the sperm of the
male to meet the sperm of the female. It occurs because of a physical inability to join the reproductive
parts of the different species and for the male to inseminate the female.
Microevolution: evolutionary change consisting in the altering of allele frequencies in a population. Can
be determined if it has occurred based on taking samples and putting the numbers into the hardy-
Migration: the movement of individuals between different populations of species that results in gene
flow. This is beneficial because it increases variation in the two populations.
Missense mutation: a point mutation in which the base pair that is substituted changes the amino acid
that the codon codes for. This changes the resulting protein configuration making the protein potentially
Morphospecies: a group of organisms that have individuals that differ in morphology but are grouped
together for analytical purposes: Bad for classifying the nematodes and some birds. Good for identifying
species in the wild. Good for classifying the fossils.
Mutation: a change in the genetic sequence or structure of an organism that happens through an error
in the genetic replication or combination mechanisms.
Natural selection: the selection of particular traits within a population that occurs because the
individuals that possess these traits are better adapted to their habitat and therefore are better able to
reproduce and pass on their genes to their offspring. It results in the increase in the allele or genotype
that is being selected for.
Neutral mutation: a mutation which confers no selective advantage or disadvantage.
Non-random mating: mating between organism in which one of the organism makes a conscious choice
to mate with a partner having a certain phenotypic trait. Sometimes females can choose what type of
males they want to mate with or sometimes males will compete with each other to determine which
male will get to mate with the female(s).
Nonsense mutation: mutation which generates one of the termination codons: UAA, UAG, or UGA
resulting in the premature termination of polypeptide synthesis during translation.
Null hypothesis: a hypothesis that tells you nothing is going on.
Parapatric speciation: a type of speciation that occurs when the populations of organisms live in
different habitats adjacent to one another. The hybrid that is produced isn’t viable in either habitat so it will die. This further enables natural selection to enhance the isolation mechanisms by which the species
will not reproduce.
Phenotype: the measurable characteristics in an organism, physical or biochemical resulting from the
genotype. This is the trait that is observed by the eye.
Phylogenetic species: the concept that states that a species is an irreducible group of organisms that
share a common ancestor. It runs into a problem because it doesn’t specify where the breaking apart of
organisms stops. There is always variation between a population so when do you stop branching?
Point mutation: mutation resulting in the change of a single base pair. Can be an addition, deletion or
substitution. Addition and deletion result in frameshift mutations while a substitution results in a
missense, nonsense or silent mutation.
Polyploidy: is a state different from most organisms which are normally diploid meaning they have only
two sets of chromosomes - one set inherited from each parent; polyploidy may occur due to abnormal
cell division (no cell division during mitosis so meiosis makes diploid gametes). It is a chromosomal
mutation. It is most commonly found in plants and is usually beneficial in plants. Can occur it two ways;
autopolyploidy or allopolyploidy. Auto occurs when a plant fertilizes another plant of the same species
and ends up with more than the diploid amount of chromosomes in the zygote. Allo occurs when the
offspring is a hybrid and makes a mistake when doing mitosis and doesn’t divide. Therefore, the zygote
Population: all the individuals living in the same area and are interbreeding.
Population genetics: the genetics that studies the allele frequencies of populations of organisms.
Post-zygotic isolation mechanisms: isolation mechanism in which the zygote that is produced isn’t viable
(the hybrid zygote doesn’t mature into an adult individual), isn’t able to reproduce (the hybrid is sterile)
or breaks down (the F1 hybrid is functional and fit but as soon as it reproduces the offspring isn’t viable)
Pre-zygotic isolation mechanisms: isolating mechanisms between different species that do not allow the
species to breed with each other and form a zygote. They are; mechanical, ecological, temporal,
gameteic and behavioural.
Recessive allele: the allele that isn’t able to express itself when paired with a different form of the allele.
Reinforcement: the process by which the hybrid formed between two different populations isn’t able to
survive so the isolation mechanisms between these two populations continues to increase and the idea
that speciation has occurred is reinforced.
Reproductive isolation: occurs when two different populations aren’t able to mate with each other and
make fertile and viable offspring. Can be pre or post zygotic.
Ring species: a species that has a geographical zone that it lives in where there is a center zone where
the species doesn’t exists because the environment doesn’t allow it to live in that area. The sub species
in the different areas of the ring have adapted to different environments and this means that they are
on their way to becoming different species. The species can reproduce with each other only where their habitats overlap. The hybrids formed might be viable or might not. The sub species have all come from a
common ancestor. If the hybrid isn’t viable then we call this reinforcement. Speciation has occurred.
Sometimes the hybrids are viable and a hybrid zone is made and sometimes the hybrid is better adapted
to the environment and out competes the parent species’.
Sexual dimorphism: the systematic difference in form between individuals of a different sex in the same
Sexual selection: the difference in the ability of individuals of different genetic types to acquire mates,
and therefore the differential transmission of characteristics to the next generations.
Sickle cell anaemia: disease developed when a person is homozygous for the sickle cell mutation in the
gene for B-globin. An abnormal haemoglobin is produced which causes sickling.
Silent mutation: a mutation which has no effect on the individual.
Speciation: the evolution of new species.
Sperm competition: type of sexual competition in animals where there is not only competition for
females but for fertilisation.
Stabilising selection: also referred to as purifying selection, is a type of natural selection in which genetic
diversity decreases as the population stabilizes on a particular trait value. Put another way, extreme
values of the character are selected against. This is probably the most common mechanism of action for
Subspecies: a population of organisms that are designated as a sub species because they have diverged
from the parent species and now live in a different geological area. This means that they don’t
reproduce with the original parent species. However, where the geographical zones overlap the sub
species have the ability to produce offspring. (ex ring species)
Sympatric speciation: speciation that occurs while the populations are still living in the same habitat and
become reproductively isolated. Usually happens when the organisms start adapting to different food
sources and end up mating with the individuals that are doing like them.
Temporal isolation: pre-zygotic isolation where the time of reproduction of the respective species is
different. Therefore, the species can never breed with each other.
Tetraploid: when an organism has two pairs of homologous chromosomes. Deleterious in animals but
beneficial in plants.
Triploid: when an organism has three sets of homologous chromosomes.
Vicariance: a geographical separation of a species that usually will end up resulting in speciation. This is
a type of allopatric speciation because the population are geographically isolated. Organising the living world:
Adaptive Radiation: evolution of a number of divergent species from a common ancestor, each species
becoming adapted to occupy a different ecological niche. The original population grows and increases in
numbers and expands in size into geographical zones that have different climates. The populations in
each habitat adapt to their respective habitats and become new species. Ex Darwin’s finches.
Advanced characters: of more recent evolutionary origin. These are characters that are derived.
Therefore, they are given a number other that zero in cladistics.
Analogous: structures that are similar in function but different in structure or evolutionary origin, like
bird and bat wings. They are made by convergent evolution and they are usually found in species that
live in similar environments. The environment favours the individuals that carry this specific trait.
Apomorphy: a character that was derived by a common ancestor and that all the descendents of the
common ancestor possess. This is often used as the defining trait for a species. When many evolutionary
taxa share this trait it is termed a synapomorphy. These synapomorphies define the monophyletic
groups (ie. Clades). The trait must be a derived trait. Can’t be the ancestral trait.
Artificial taxonomy: classification that organisms are related based on a few convenient characteristics
rather than one the basis of evolutionary relationships. Basically, this type of taxonomy was a list of
organisms with traits that define them so that you would be able to distinguish them if you see one. This
type of taxonomy originated when the greek philosophers wrote down the folk taxonomy. It allowed for
more than 500 objects to be classified (good for commerce and travel). It was done by Aristotle and all
the people that made the compendiums.
Autoapomorphy: This is an apomorphy that is present in only one taxa or clade. It must be a character
that was derived from the pleisomorphic state of the common ancestor.
Binomen: The two name classification system that was created by Linnaeus when he created his
mechanical taxonomy. The first name was a noun and the second an adjective. The classification
method relied on the morphology of the organisms.
Camera eye: type of eye that is present in only the vertebrates and the molluscs. The trait is analogous
and a homoplasy because it was made twice during evolution. This is a type of convergent evolution.
There were originally two ways to explain how the eye was formed. The convergent explanation was
taken over the explanation that the eye was reversed five times by the other taxa because the
convergent explanation has less evolutionary events that occur in it. This is an example of parsimony.
We accept the most probable explanation.
Character convergence: the condition in which two newly evolved species interact in such a way that
one or both converges in one or more traits towards the other. The structures formed are analogous to
each other and are called homoplasies because they didn’t arise from the same common ancestor. This
usually occurs when the two species live in similar environments. Ex. the camera eye. Character polarity: explains the evolutionary change in a character. This describes which character is
primitive and which is derived. We assign polarity to characters to determine which one came first so
that we can determine which species is primitive and which is ancestral. This is the basics of cladistics
created by William hennig.
Character reversal: this is an occurrence where the apomorphy that was derived from the plesiomorphy
(the ancestral state) returns back to the plesiomorphy. This is an example of a homoplasy. Basically the
clade loses the character that is has gained.
Clade: A lineage branch that results from the splitting of an earlier common lineage shared by the taxa
that branched. The clade is defined by a character that is exclusive to it and all of its members
distinguishing it from the rest. An example is a monophyletic group.
Cladistics: a method of classification that uncovers genealogic relationships based on the homologous
characters that species’ share and the polarity of these characters (whether they are derived or
ancestral). The species are always compared to a sister group that is considered to be ancestral and all
the traits that it possess is also considered to be ancestral. This means that the other organisms similar
to it are compared to it to determine the phylogenetic tree that represents the relationships between
the species. Made by henning. Also created new terms like apomorphy and synapomorphy ect.
Cladogram: the diagram used to represent the evolutionary relationships between a set of species based
on assigned character states. It attempts to uncover the evolutionary sequence of the group of
organisms. The nodes represent a common ancestor to the subsequent branches in the diagram.
Classical taxonomy: concerned primarily with the description, naming, and classification of organisms
based on their morphological characteristics. However, these morphological characters were used to
determine which species were evolutionarily primitive. This type of taxonomy came to be very bias
because the biologists had to determine which traits should be used to determine which organism was
Classification: the organization of things into groups.
Common ancestor: a species that gives rise to two or more new species. This is the species that evolved
into two different species. It represented by a node on a cladogram.
Convergent evolution: similarity between two organisms due to independent evolution along similar
lines rather than from a common ancestor. The traits that have converged are referred to as
homoplasies. Usually occurs due to environmental stress placed on an organism.
Dendrogram: branching tree-like diagram used to classify organisms. It classified things in groups and
more importantly hierarchies. An example is the scalae naturae.
Derived characters: not present in the ancestral stock. These can be referred to as apomorphies or
synapomorphies base on the number of taxa that share the character. Taxa that share the derived
character coming from the same common ancestor are said to be part of the same monophyletic group. Dichotomy: branching that results from division. The division must have two options at every step. This
type of division is used in cladistics when the character traits are assigned polarities; ancestral or
derived. Also used by many organisms on the planet in their day to day lives.
Divergent evolution: evolutionary change tending to result in differences between two species. This type
of evolution can occur in many ways. It also leads to speciation. The organisms can diverge based on a
change in habitat. Divergence usually occurs after events like vicariance and migration to a new land.
Once species leave a large population and go to a smaller one they are prone to the effects of genetic
drift and will probably diverge. This also occurs in the ring species.
Evolutionary taxonomy: classify organisms using a combination of phylogenetic relationship and overall
similarity. It differs from strict cladism where all taxa in a classification always should include all
descendants of a single ancestral node. It thus allows for paraphyletic taxa. As evolutionary
systematicists define terms, paraphyletic taxa are monophyletic too, in the sense that they derive from a
single common ancestor, just not holophyletic, meaning that all descendants are included (which is
monophyletic according to the cladistic definition).
Folk taxonomy: the way rural or indigenous peoples make sense of and organize their natural
surroundings/the world around them, typically making generous use of form taxa like "shrubs", "bugs",
"ducks", "ungulates" and the likes. Always consisted of about 500 objects and was usually around three
tiered. The classification system was usually remembered by a select number of people in the tribe.
Fungi: are heterotrophic organisms possessing a chitinous cell wall. The majority of species grow as
multicellular filaments called hyphae forming a mycelium; some fungal species also grow as single cells.
Sexual and asexual reproduction of the fungi is commonly via spores, often produced on specialized
structures or in fruiting bodies.
Hierarchical: at type of classification that gives order to which thing cam before which. In other words, it
explains which taxa are contained within the same taxa (ie. Share a common ancestor). Things are put in
Henning: the man that invented cladistis in order to eliminate bias in determining the evolutionary
sequence of different species. Was germen.
Homologous: structures that resemble each other because of common ancestry. Occur do to divergent
evolution. The structures share a homology. The structures can have different functions.
Homology: resemblances due to common descent. The traits are homologous and occur due to
Homoplasy: resemblances between organisms due to evolution along different lines rather than
common descent. Traits are analogous and occur due to convergent evolution.
KISS principle: The principle that is used when trying to resolve conflicts in cladistics. The principle states
that the explanation of the occurrence is the explanation that requires the least amount of evolutionary
change to have occurred. This is also called p