Test 2 LOs: MICROEVOLUTION
i) GENETIC VARIATION & MUTATION & HARDY-WEINBERG PRINCIPLE
Define key terms:
Population: all individuals of a single species that live together in the same place and time
Microevolution: changes in genetic characteristics of a population over time (traits depend on
genetics and environment); occurs in a shorter time compared to macroevolution; occurs when
the allele frequencies in a population change
Phenotypic Variation: differences in appearance or function between individual organisms
Qualitative Variation: variation that exists in two or more discrete states, with intermediate
forms often being absent
Quantitative Variation: variation that is measured on a continuum (such as height in human
beings) rather than in discrete units or categories
Mean Value of Characteristic: average value of the characteristic
Explain why variation in populations is important to evolution.
In order for evolution to occur, there must be genetic variation that is heritable. e.g. fly
-variation in starvation resistance (variation)
-after each generation, more flies survived longer (heritable)
Classify a phenotypic character as exhibiting quantitative or qualitative variation.
Examples of quantitative variation: height, weight, toe length, number of hairs on head
Examples of qualitative variation: snow geese (either white or blue), blood type (A or B or AB or
- Two individuals of the same species can have different genotypes, but have the same
This can occur due to the environment. If two individuals that have different genotypes, they
may have the same phenotype if they live in similar environments.
-And how two individuals could have the same genotype, but different phenotypes.
This can also occur due to the environment. Although two individuals may have the same
genotypes, their phenotypes may differ if they live in different environments. (e.g. pH of the
soil can affect the colour of certain flowers) Interpret from a graph of a quantitative character, the degree of variation for that character
within the population.
The width of the base of the graph is proportional to the degree of variation. (wider
Describe, in simple terms, several ways in which variation is generated.
Crossing over during meiosis
Independent assortment during meiosis
Fertilization may generate variation (half of chromosomes are from mom, half of
chromosomes are from dad)
Mutations are the ultimate source of variation (They can modify an allele to another
allele that already exists in the population, they can create a new allele that doesn’t
exist in the population of interest and codes for the production of a new protein);
mutations arise from random processes
-The random nature of mutations; how mutations are passed on from one generation to the
next (both vertically & horizontally)
Vertically: (Meiosis) chromosomes may not segregate properly during anaphase I and/or
anaphase II leading to mutations that may be passed on to the next generation.
Horizontally: If a mutation occurs in the replication of a plasmid, it may be passed on to another
bacteria and when that bacteria replicates, it will pass on the mutation to the next generation.
-And the role of mutation in evolution
Mutation can restore variation removed by other evolutionary processes. It also provides the
raw material for evolution (mutation-random, natural selection-not random)
Gene Duplication: A portion of the genetic material is duplicated or replicated resulting in
multiple copies of that region.
Pseudogene: looks like a gene but doesn’t act like one; not expressed (Dr. Kelly), a pseudogene
is a DNA sequence that resembles a gene but has been mutated into an inactive form over the
course of evolution.
Gene family: genes similar to each other in structure and function (Dr. Kelly) Explain how gene duplication can lead to evolutionary change.
Outcome of gene duplication that could lead to evolution of novel traits:
-may retain original function, but change in expression pattern (new tissues/developmental
-duplicated gene gains mutationsaltered protein product could perform valuable function
e.g. copy B can bind new substrates
Evolutionary Developmental Biology (‘evo-devo’): a field of biology that compares the genes
controlling the developmental processes of different animals to determine the evolutionary
origin of morphological novelties and developmental processes
Genetic tool-kit (i.e., homeotic genes): Homeotic genes are regulatory genes that code for
transcription factors that bind regulatory sites on DNA, either activating or repressing the
expression of other genes that contribute to an organism’s form; Comparisons of genome
sequence data reveal that most animals, regardless of their complexity or position in the tree of
life, share a set of several hundred homeotic genes that control their development. This
“genetic tool-kit” governs the basic design of the body plan by controlling the activity of
thousands of other genes.
Explain, using a very general example, how changes in developmental regulatory genes can
be a genetic switch between different morphologies. (Explain how small genetic changes
could account for large changes in the characteristics of organisms and lead to new
-Gene switchesinitial determinants of which genes are turned on/off in different body areas
and cell types
-By altering timing of a developmental gene (where/how long)can manifest huge changes to
-e.g. turn of ONE hox genedifferent set of wings (Dr. Kelly’s insect example)
Gene Pool: the sum of all alleles at all gene loci in all individuals in a population
Genotypic Frequency: the percentage of individuals in a population possessing a particular
Allele Frequency: the abundance of one allele relative to others at the same gene locus in
individuals of a population
Relative Abundance: the relative commonness of populations within a community Genetic Equilibrium: the point at which neither the allele frequencies nor the genotype
frequencies in a population change in succeeding generations
Loci/locus: the particular site on a chromosome at which a gene is located
Fixation/Loss: If there is only 1 allele, frequency=1; fixed (Dr. Kelly); In population genetics,
fixation is the change in a gene pool from a situation where there exist at least two variants of a
particular gene (allele) to a situation where only one of the alleles remains.
Differentiate between genotype frequency and allele frequency.
Genotype frequency is the percentage of individuals (relative abundance) in a population
possessing each genotype for a given locus (gene). Allele frequency is the relative abundance of
different alleles for a gene within a population.
Calculate frequencies of alleles or genotypes given information on the number of individuals
with specific genotypes.
p +2pq+ q = 12
e.g. There are 2 alleles in a population: A1and A .2There are 4 A A1 2, A a2 2, A A Cal1 1.te
the allele frequencies.
Total number of alleles=20
Frequency of A =10/20=0.5, Frequency of A =10/22=0.5
Explain how the Hardy-Weinberg (HW) principle acts as a null model/hypothesis for
(Using the 5 assumptions describing population)
-If evolution was NOT occurring, there would be no mutations because they are mechanisms of
-If evolution was NOT occurring, the population would be isolated from other populations
which would prevent gene flow-another mechanism of evolution.
-If evolution was NOT occurring, there would be no natural selection (mechanism of evolution)
with respect to the gene of interest; all genotypes in the population survive and reproduce
-If evolution was NOT occurring, there would a population that is infinite in size (extremely
large) meaning that the effects of genetic drift (mechanism of evolution) are minimal. List the 5 conditions of the HW principle under which a population of diploid organisms can
reach genetic equilibrium.
1. No mutations are occurring
2. The population is closed to migration from other populations
3. The population is infinite in size
4. All genotypes in the population survive and reproduce equally well
5. Individuals in the population mate randomly with respect to genotypes
Explain why microevolution will not occur under the conditions of HW.
Under the conditions of HW, frequencies of alleles (and genotypes) are preserved from
generation to generation in populations and thus microevolution will not occur.
ii) NATURAL SELECTION & ADAPTATION
Define: natural selection, artificial selection, adaptation, fitness, relative fitness, stabilizing
selection, directional selection, disruptive selection, fitness trade-off, adaptive radiation.
Natural Selection: evolutionary process by which alleles increase likelihood of survival and the
reproductive output of the individuals that carry them become more common in subsequent
Artificial Selection: selective breeding of animals or plants to ensure certain desirable traits
appear at higher frequency in successive generations.
Adaptation: characteristic(s) that helps an organism survive longer or reproduce more under a
particular set of environmental conditions.
Fitness: an organism’s ability to survive and reproduce in a particular environment.
Relative fitness: The number of surviving offspring that an individual produces compared with
the number left by others in population.
Stabilizing selection: a type of natural selection in which individuals expressing intermediate
phenotypes have the highest relative fitness.
Directional Selection: a type of selection in which individuals near one end of the phenotypic
spectrum have the highest relative fitness.
Disruptive selection: a type of selection in which extreme phenotypes have higher relative
fitness than intermediate phenotypes.
Fitness trade-off: compromise between traits. An advantageous trait also has a disadvantage
side to it. See examples at bottom.
Adaptive Radiation: the diversification of a group of organisms into forms filling different ecological niches (status of organism within its environment).
Explain the importance of genetic variation to the process of natural selection.
Because of genetic variation, certain alleles are more favored than others (natural selection). If
there’s no genetic variation, how can an allele be favored amongst others, if there’s only one
allele in the population. No genetic variation means they are all “equally fit”.
Explain how natural selection acts on phenotypic variation to alter the genetic structure of a
When certain phenotypes are favored, they are passed on more to the next generation, which
is changing the genetic structure of a population. Phenotypes result of genes, so if phenotypes
are favored, those genes that produce those phenotypes are favored as well.
Differentiate between artificial selection and natural selection. [Knowledge, Comprehension,
Artificial selection is selecting certain alleles to be greater in the next generation (selective
breeding) and natural selection is process by which favorable heritable traits become more
common in successive generations of a population of reproducing organisms, and unfavorable
heritable traits become less common, due to differential reproduction of genotypes. Basically,
we can control artificial selection but not natural selection.
Artificial selection: Breeding for a small dog such as a chihuahua.
Natural selection: Bird whose beak after a generation or more changes so it can feed on the
food available to survive.
Explain how artificial selection provides evidence for natural selection. [Comprehension]
It demonstrates conclusively that if individuals in a population consistently have differences in
reproductive success based on *inherited* traits, generation after generation, then that
population will slowly change over time and those traits will become more universal. That is
precisely the essential claim of natural selection.
Describe what is meant by ‘descent with modification’. *Comprehension+
Descent with modification refers to the passing on of traits from parent organisms to their offspring.
Explain why individuals do not evolve and why evolution is considered a population process.
Evolution and natural selection is a long process covering many hundreds, thousands, even
millions of generations. The evolutionary process cannot take place in an individual because the
individual represents only one generation.
Differentiate between evolution and natural selection. [Comprehension, Analysis]
Evolution is a gradual process in which something changes into a different and usually more
complex or better form whereas natural selection is a mechanism in nature by which, according
to Darwin's theory of evolution, only the organisms best adapted to their environment tend to
survive and transmit their genetic characteristics in increasing numbers to succeeding
generations while those less adapted tend to be eliminated.
Explain why reproduction is more important than survival to an old age in terms of evolution
by natural selection. [Comprehension, Analysis]
For natural selection to occur, the parent has to pass on its favorable traits to its offspring, if it
does not reproduce it is not contributing to their next generation. Survival of the fittest means
surviving to reproduce.
Describe how the process of natural selection is non-random. [Comprehension]
Natural selection is non random because of the fact that favorable traits are passed on, not any
trait. It is because these traits helped them (population) to survive that they are passed on,
there is a reason.
Explain why evolution is not progressive (e.g., moving towards ‘perfection’).
Evolution is progressive in the sense that it keeps a population of organisms "tuned" to its
environment. If the environment changes too rapidly for a population of organisms to
genetically adapt, they lose their fitness and go extinct no matter strong they are.
Describe how natural selection results in adaptation of populations. [Comprehension]
Adaptation is/are trait(s) that allow individuals to out produce individuals without those traits.
Natural selection passes on these traits because their parents had used these traits to out produce as well.
Describe why there are limits to adaptive evolution (i.e., why organisms can never be
perfectly adapted to their environment). [Comprehension] An organism can never be perfectly
adapted to the environment because environment changes sometimes due to chance events
(hurricanes) and etc.
Explain why a character that is strongly influenced by the environment would not respond to
selection (either artificial or natural). [Comprehension]
Explain why natural selection usually exerts little effect (i.e., weak selection) on a genetically-
determined phenotype that appears in post-reproductive life. [Comprehension/Analysis]
When you are in your post-reproductive life, you do not contribute to the next generation. If
anything happens to you, it won’t matter because your not passing any traits on to the next
generation anyway, not in stage to reproduce. Example Huntington’s disease affect females
after 40 yrs. of age, but that will not matter because natural selection will only affect the
offspring not the parent because it wont contribute to the next generation.
Compare and contrast the different types of selection (e.g., directional, etc.), discussing their
effects on genetic variation and mean character value within a population.
1) Directional selection: when individuals near one end of phenotypic spectrum have the
highest relative fitness.
The mean value shift towards the extreme, either lower or higher than before
Decreases genetic variation.
2) Stabilizing selection: when individuals expressing intermediate phenotypes (middle) have the
highest relative fitness.
Eliminates phenotypic extremes (at ends of phenotypic spectrum)
Decrease genetic and phenotypic variation and increases frequency of intermediate
3) Disruptive selection: when extreme phenotypes (both ends) have higher relative fitness.
Alleles producing extreme phenotypes become more common promoting polymorphism.
Genetic variation higher than other types of selection.
Identify, given a scenario, which form(s) of natural selection is/are at work. [Analysis]
don’t know how to explain this :S Predict, given a description, the outcome of a scenario/experiment if selection is acting.
[Comprehension, Analysis, Application]
There is selection if certain traits are passes on more than others. Will notice a change in
genetic frequency, and phenotypic frequency.
Discuss adaptations, commenting on why: there are limits to adaptation; not all traits are
adaptive; why adaptation is not universally good; adaptations always represent compromises
(how an organism’s phenotype represents a compromise or ‘trade-off’ between the adaptive
value of multiple traits. [Comprehension]
An adaptation is a feature that is common in a population because it provides some improved
function. Adaptations are well fitted to their function and are produced by natural selection.
Limits to adaptions because the environment is always changing. Adaptions are not universally
good because one adaption may be good for some function but not another. May not be good
in all environments.
Provide an example of a fitness trade-off. [Knowledge]
One example is an organism being slower in order to have a larger body size. The larger body
size may be beneficial for fighting predators but it makes the organism slower.
Example in class: gill guppies like longer gonopodia in males but that increases their chances of
getting eaten by predators.
iii) MAINTENANCE OF GENETIC VARIATION (HETEROZYGOTE ADVANTAGE, ETC)
Explain why alleles coding for dominant traits don’t, through natural selection, always
replace recessive or rare alleles. [Comprehension, Analysis]
Dominant traits don replace them because recessive or rare alleles will come up because of
genetic drift (chance)
Describe how diploidy can hide harmful recessive alleles from natural (or artificial) selection.
Haploid can only have one allele so it cannot hide the harmful recessive allele. **In diploid harmful recessive alleles are disadvantageous in a homozygous state, but in a
heterozygous state, the recessive allele can be masked because of the expression of the
dominant allele. Diploid state preserves recessive allele at low frequency in large population,
doesn’t eliminate them. In small population, the combination of natural selection and genetic
drift can eliminate them.
Describe how spatial and temporal environmental variability can influence population
variation. [Comprehension, Analysis]
In temporal variability different alleles will be favored in different environment. At a different
time of the year, a different phenotype selected. Ex: camouflage white fox will be good in
winter, but not in spring.
In spatial variability, there will be a greater change in characteristics along the geographic line.
Describe heterozygote advantage and frequency-dependent selection. [Comprehension]
Heterozygote advantage: describes a mechanism by which a recessive allele, though harmful in
the homozygous condition, is maintained in a population because it provides some adaptive
advantage in heterozygotes.
Example is sickle-cell disease. Individuals’ homozygous recessive (ss) for the sickle-cell allele are