MICROEVOLUTION
1) GENETIC VARIATION & MUTATION & HARDY-WEINBERG PRINCIPLE
1) Define key terms: population, microevolution, phenotypic variation, qualitative and quantitative variation,
mean/average value of characteristic. [Knowledge]
-Population: All individuals of a single species that live together in the same pale and time
-Microevolution: small- scale genetic changes within populations, often in response to shifting environmental
circumstances or chance events.
-Phenotypic variation: Differences in appearance or function between individual organisms Ex difference in mass
or length of a shell, variations in individual biochemistry, physiology, internal anatomy, behavior - Phenotypic
traits exhibit either quantitative or qualitative variation within populations of all organisms
-Qualitative variation (Discrete); Variation that exists in two or more discrete states with intermediate forms often
being absent. Ex Flower color either purple or white; Blood type A or B or AB, You are either 6 foot or 5 foot ,
nothing else.
-Quantitative variation (continuous): Variation that is measured on a continuum rather than discrete units or
categories. - individuals differ in small, incremental ways Ex In my biology class height, weight, toe lengths, # hairs
on heads.
-Mean/average value of characteristic: The average value of a characteristic in a population, the middle, the peak
of the bell curve (The mean; describes the average value of the character)
2) Explain why variation in populations is important to evolution. [Comprehension]
Variation is important because it is a strong contributor to evolution. Through variation within a population
individuals vary in genetics. If genotypic, these more advantageous variations (better adaptations to environment)
will be favored by natural selection, thus resulting in the increase of the frequency (allele) of these traits. Thus
through evolution (microevolution) overtime these changes can result in it becoming the dominant in the population.
Basically without variation, natural selection would have nothing to favor and pass on (no advantageous trait) = no
evolution (everyone stays the same)
3) Classify a phenotypic character as exhibiting quantitative or qualitative variation. [Comprehension]
Quantitative = gradual continuum of variation in a trait Ex height, weight, skin tones, # of hairs in humans
Qualitative = discrete variations in traits, no intermediates Ex Snow geese are either Blue or white.
4) Explain how: two individuals of the same species can have different genotypes, but have the same
phenotype; and how two individuals could have the same genotype, but different phenotypes.
[Comprehension]
- We can have genetic and environmental causes on phenotypic variation
1. Organisms with different genotypes exhibit the same phenotype (Diff G, same P); different genes (possibly
mutated) cause the same trait. Ex mice in Arizona are black due to mutation in gene BUT ARE NOT RELATED
mice in New Mexico who are also black, but different gene [even though they both have the same phenotype, have
different genotypes ( don't share the mutation)]
2. Organisms with the same genotype can exhibit the same phenotype (Same G, diff P); influenced by the
environment Ex Flower color influenced by pH of soil
5) Interpret from a graph of a quantitative character, the degree of variation for that character within the
population. [Application, Analysis]
- We display data on quantitative variation in a graph; The width of the curve is proportional to the variability
(amount of variation) amongst individuals; 1. A broad, low curve indicates a lot of variation among individuals 2. A
high, narrow curve indicates little variation among individuals Ex
6) Describe, in simple terms, several ways in which variation is generated. [Comprehension]
Genetic variation arises within populations largely through mutation (new alleles) and genetic recombination
(rearrangement of existing alleles)
1. Production of new alleles: Mutations
2. Rearrangement of existing alleles: Crossing over (during meiosis); shuffles segments on the chromosomes
Independent assortment (arrangement along metaphase plate); shuffle whole chromosomes (each homologous
pair shuffles independently) Random fertilization between egg and sperm. 7) Explain: the random nature of mutations; how mutations are passed on from one generation to the next
(both vertically & horizontally); and the role of mutation in evolution. [Comprehension]
-Mutation; is a heritable change in DNA (Effect on genetic variation; Introduces new genetic variation into
population; mutation is a major source of heritable variation)
- Very rare, but creates variation – mutations can be passed down through DNA
- Mutations are random and can occur at any place on the chromosome they don‟t appear because they are needed.
-Random Mistakes during gene duplication is one way mutations can occur.
If Deleterious mutations; (alter an individual‟s structure function or behavior in harmful ways ); even if
passed down, probably will be eliminated from population since individual doesn't reproduce (decrease fitness)
If Advantageous; (confers some benefit on an individual that carries it) ; Natural selection may preserve
the new allele and even increase its frequency over time
If Neutral Mutations: (are neither harmful nor helpful) persists since it doesn't affect survival or
reproduction
- Since Mutations cause variation, it can cause evolution
Natural selection will choose specific traits over others, so beneficial mutations which code for that trait
will be passed down, becoming more common (microevolution)
Vertically- mutations are passed from one generation to the next *parent splits into daughter cells*
Horizontally- genes are passed from one species to another Ex bacteria exchange DNA directly, which
can then be passed down t all calls derived (binary fission) from it.
8) Define gene duplication, pseudogene and gene family; explain how gene duplication can lead to
evolutionary change. [Knowledge, Comprehension]
-Gene duplication; process by which an existing gene is copied in the DNA
- Pseudogene; Genomic sequences similar to existing genes that serve no function (no protein-coding ability)
“false gene”
-Gene family; a set of several similar genes, derived from the duplication of a single, original gene, and generally
with similar functions.
-Explain how gene duplication can lead to evolutionary change;
If a gene is duplicated, one may continue to function as usual (the original) while the other may mutate.
Could become nonfunctioning gene (pseudogene)
could gain a different function
source of new genes microevolution (heritable traits).
9) Define: evolutionary developmental biology (‘evo-devo’), genetic tool-kit (i.e., homeotic genes). [Knowledge]
-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); Set of several hundred homeotic genes that control the development of
organisms; common in most animals governs design of body by controlling the gene activity
10) 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 morphologies.) [Comprehension] [How small changes in
genes = large change in char]
- Homeotic genes; Code for transcription factors that bind to regulatory sites of DNA active/ repress other genes
downstream.
Could be mutations of reg genes = change in expression = change in morph
if diff sites are binded by transcription factors, different, combos of expression results in formation of
different structures in embryo
Ex Hox genes determines appendages )where, what) by producing transcription factors
Same genes in many organism but makes different structures (ie wings vs legs)
Expresses genes in location where appendage grows
Ex In fish Hox D inly active ones In tetrapod‟s Twice 11) Define: gene pool, genotypic frequency, allele frequency, relative abundance, genetic equilibrium,
loci/locus, fixation/loss. [Knowledge] (17.2A)
-Gene pool; The sum of all alleles at all gene loci in all individuals in a population
- To describe the structure of a gene pool, scientists first calculate genotype frequencies; the percentages of
individuals possessing each genotype. Ex C R W 500 Indiv 0.5
CRC R 450 Indiv 0.45 => 0.5 + 0.45 +0.05 = 1
C W =W50 Indiv 0.05
/ 1000
- Knowing that each diploid organism has two alleles (either two copies of the same or two different allele) at each
gene locus, a scientists can the calculate - Allele frequency; The abundance of one allele relative to others at the
same gene locus in individuals of a population p ; frequency of one allele, q frequency of the other For each
gene locus with two alleles there are 3 genotype frequencies ( pq, pp, qq (sum of 3 geno freq must equal 1), but only
two allele frequencies (p and q (sum of these 2 allele freq must equal1)
Ex p= CR (600 x 1) + (450 x 2) + (50 x 0) = 1400 / 2000 alleles = 0.7
q= CW (500 x 1) + (450 x 0) + (50 x 2) = 600 / 2000 alleles = 0.3 p + q = 0.7 + 0.3 =1 FIGURE 17.1
-Relative abundance; the relative commonness of populations within a community (ie. alleles with genelocus)
- Genetic equilibrium; the pt. at which neither allele nor genotype frequencies in a population change in succeeding
generations.
-Loci/locus; a particular gene location on a chromosome in diploids, each, locus has 2 alleles [In diploid
organisms (have 2 pairs of homologous chromosomes) an individuals genotype includes two alleles at every gene
locus]
-Fixation/loss; alleles with a frequency of 1 are fixed; lost have frequency of 0
12) Differentiate between genotype frequency and allele frequency. [Knowledge, Comprehension]
-Genotype frequencies; the percentages of individuals possessing each genotype.
- Allele frequency; The abundance of one allele relative to others at the same gene locus in individuals of a
population
genes can have more than one allele therefore frequency different fro allele
Genotype frequencies- the percentage of individuals in a population possessing a particular genotype.
are the frequencies of the homozygous dominant (AA) heterozygous (Aa) and homozygous recessive
2 2
(aa). If you're using population genetics, then they are the p , 2pq, and q values.
Allele frequencies are the frequencies of each allele, dominant (A) and recessive (a). In population genetics these are
p & q.
13) Calculate frequencies of alleles or genotypes given information on the number of individuals with specific
genotypes. [Application]
- To describe the structure of a gene pool, scientists first calculate genotype frequencies; the percentages of
individuals possessing each genotype. Ex C R W 500 Indiv 0.5
C C = 450 Indiv 0.45 => 0.5 + 0.45 +0.05 = 1
R R
C W =W50 Indiv 0.05
/ 1000
- Knowing that each diploid organism has two alleles (either two copies of the same or two different allele) at each
gene locus, a scientists can the calculate - Allele frequency; The abundance of one allele relative to others at the
same gene locus in individuals of a population p ; frequency of one allele, q frequency of the other For each
gene locus with two alleles there are 3 genotype frequencies ( pq, pp, qq (sum of 3 geno freq must equal 1), but only
two allele frequencies (p and q (sum of these 2 allele freq must equal1)
Ex p= CR (600 x 1) + (450 x 2) + (50 x 0) = 1400 / 2000 alleles = 0.7
q= CW (500 x 1) + (450 x 0) + (50 x 2) = 600 / 2000 alleles = 0.3 p + q = 0.7 + 0.3 =1 FIGURE 17.1
14) Explain how the Hardy-Weinberg (HW) principle acts as a null model/hypothesis for evolution.
[Comprehension]
-The Hardy- Weinberg principle (is a null model) specifies the conditions under which a population of diploid
organisms achieves genetic equilibrium, (the point at which neither allele frequencies nor genotype frequencies
change in succeeding generations) Null model since it shows when evolution, which changes allele frequencies, doesn't occur
2 - ref2rence point evaluating circumstances under which evolution may occur.
P +2pq+q ; HW principle acts as a null hypothesis because it demonstrates an ideal situation where no
evolution is occurring (Studies that use observational use this instead of control)
15) List the 5 conditions of the HW principle under which a population of diploid organisms can reach genetic
equilibrium. [Knowledge]
HW; is a null model that describes the conditions under which microevolution will not occur:
1) no mutations occurring 2) No migration in and out 3) pop is infinite in size 4) all genotypes survive & reproduce
equally 5) Mating is random
[1) Mutations do not occur 2) Populations are closed to migration 3) Populations are infinitely large 4) All genotypes
in the population survive and reproduce equally well (Natural Selection does not operate) 5) Individuals select mates
at random ( with respect to genotypes) ]
16) Explain why microevolution will not occur under the conditions of HW. [Comprehension]
- No new alleles through mutation, all survive allele frequency never changes, thus can be no change in genetic
makeup of population [All 5 of the above points are mechanisms of microevolution therefore if no mechanisms of
evolution are acting on a population, evolution will not occur and the gene pool frequencies will remain unchanged]
2) NATURAL SELECTION & ADAPTATION (several of these are modified from earlier sections to show
you how the material ties together)
1) Define: natural selection, artificial selection, adaptation, fitness, relative fitness, stabilizing selection,
directional selection, disruptive selection, fitness trade-off, adaptive radiation. [Knowledge] 17.3D
-Natural selection; The evolutionary process by which alleles that increase the likelihood of survival and
reproductive output of healthy fertile individuals that carry them become more common in subsequent populations.
-Artificial selection; Selective breeding of animals or plants to ensure that certain desirable traits appear at a higher
frequency in successive generations ex breeding animal for, breed bigger ones.
-Adaptation; Characteristic or suite of characteristics that helps an organism survive longer or reproduce more under
a particular set of environmental conditions (only advantageous in specific environment)
-Fitness; The ability of an individual to survive, and reproduce healthy offspring (fertile) to carry on DNA
(measured by # of healthy offspring)
-Relative fitness; The # of surviving offspring that and individual produces compared to the # left by others in the
population alleles of more fit individual is more likely to be selected for and passed on
Three modes of natural selection have been identified: 1) Directional Selection, 2) Stabilizing selection, and 3)
Disruptive selection.
1) Stabilizing selection; type of natural selection in which individuals expressing intermediate phenotypes have the
highest relative fitness (By eliminating phenotypic extremes, stabilizing selection reduces genetic and phenotypic
variation and increases the frequency of intermediate phenotypes) Stabilizing selection, affecting many familiar traits
Ex very small or large human newborns are less likely to survive than those born at an intermediate mass.
2) Directional selection; type of natural selection in which individuals near one end of the phenotypic spectrum has
the highest relative fitness. (Directional selection shifts a trait away from the existing mean and toward the favored
extreme. After selection the traits mean value is higher or lower than before) EX predatory fish promote this for large
guppies, since they feed on the smallest guppies in pop. Ex2 Human use this to produce crops and animals with
desired traits.
3) Disruptive selection; type of selection in which individuals with the extreme phenotypes have higher relative
fitness than intermediates. (Thus, alleles producing extreme phenotypes become more common, promoting
polymorphism) Ex Galapagos finches, the extreme bill phenotypes appeared to feed efficiently on specific resources
(establishing disruptive selection on size and shape of bill) When drought = strong, When Non drought = small
-Fitness trade-off; trade between trait that helps survival in one aspect, and is disadvantageous in another ex long
feather tail – good for attracting mates – bad for escaping predators etc
-Adaptive radiation;
2) Explain the importance of genetic variation to the process of natural selection. [Comprehension] (same as 2
in i) Without genetic variation all the species would be the same and natural selection would not be able to favor
certain alleles. By having different genetic combinations, individuals of a population exhibit different traits, which may or may not be to their benefit. These more advantageous genetic variations will be favored by natural selection,
which increase of the frequency.
3) Explain how natural selection acts on phenotypic variation to alter the genetic structure of a population.
[Comprehension]
- specific phenotypes selected by natural selection thus genotype for it selectedmore common in population
[Its is the phenotypic differences which determine whether an individual is advantageous over another. Phenotypic
variation include being faster, stronger, having better eyesight. Natural selection than favors those advantageous
traits and the traits chosen are then increased in the next generation causing the genetic structure of the population to
change]
4) Differentiate between artificial selection and natural selection. [Knowledge, Comprehension, Analysis]
-Natural selection; The evolutionary process by which alleles that increase the likelihood of survival and
reproductive output of healthy fertile individuals that carry them become more common in subsequent populations.
-Artificial selection; Selective breeding of animals or plants to ensure that certain desirable traits appear at a higher
frequency in successive generations ex breeding animal for, breed bigger ones.
Same but artificial is done by humans, while natural occurs in its own based on the environment
[Natural selection is the mechanism of evolution, the process in nature by which only the organisms that are best adapted to their
environment tend to survive and transmit their genetic characteristics to the next generation. Individuals less well adapted to their
environment tend to be eliminated. - Artificial selection is when we, humans, act as the “environmental pressure.” An example is
when we choose dogs with certain traits and breed them together to emphasize the traits we desire.]
5) Explain how artificial selection provides evidence for natural selection. [Comprehension]
When traits are selected for and breed, it becomes more common in offspring In natural = environment
selects
[Because artificial selection is like a controlled lab experiment for natural selection. Ex Artificial selection shows that by breeders
purposefully selecting particular individuals to mate, based on phenotypes the breeders deem desirable, that large degrees of
morphological change can be produced. The analogy is that instead of a human doing the selecting as in artificial selection, in
natural selection the environment does the selecting. It tends to weed out the less 'desirable' phenotypes and to retain and spread
the more "desirable" phenotypes ("desirable" actually being fitness)]
6) Describe what is meant by ‘descent with modification’. [Comprehension]
Descent with modification; is an biological evolution; states that all life is related by a common ancestor however
through modification and selection different species began to emerge.
7) Explain why individuals do not evolve and why evolution is considered a population process.
[Comprehension]
Genes in an individuals DO NOT CHANGE thus no evolution Since certain traits enable some
individuals to survive, reproduce, & pass on DNA changes the populations genetic makeup with evolution
over time.
[Firstly evolution is a process over a million years! Species change (evolve) and although each individual dies
with the same genes it was born with some individuals survive better than others and reproduce more. Those
individuals with the advantageous traits will produce more offspring. Over time as the advantageous traits increase in
the next generation the overall traits of the population increase.]
8) Differentiate between evolution and natural selection. [Comprehension, Analysis]
Natural selection is a mechanism of evolution! - describes how characteristics are more common in population
overtime (fitness) –Evolution is an actual change in species (characteristics) over generations – Genetic drift, chance
(can effect evolution)
9) Explain why reproduction is more important than survival to an old age in terms of evolution by natural
selection. [Comprehension, Analysis]
- Must survive AND reproduce to pass on genes (alleles) and contribute to genetic makeup of next generations
Ex If one survives and produces more off spring than dies at a young age they have a higher survival than
someone who lives to an old age and has no off spring. Therefore reproduction determines which
organisms increase in later generations not necessarily how long they live. 10) Describe how the process of natural selection is non-random. [Comprehension]
- Selection occurs based on alleles (traits) they have The more fit, the more likely for the allele to be selected for
[Natural selection is not random in that it selects for specific individuals who posses traits advantageous to them]
11) Explain why evolution is not progressive (e.g., moving towards ‘perfection’). [Comprehension]
Evolution does not progress towards perfection cause Evolution operates via chance occurrences, like mutations
and random fluctuations in populations, and by natural selection. Mutations and random events (i.e., a huge volcano
explodes and vaporizes a population indiscriminately) are clearly not progressive events. They're random.
Natural selection works by creating a filter through which the organisms that are most fit, leave the most offspring.
Environments change constantly, and since N.S. only promotes adaptations to the conditions immediately at hand, it
is not progressive. Evolution has no foresight.
12) Describe how natural selection results in adaptation of populations. [Comprehension] 17.5A?
-Adaptive trait; is any product of natural selection that increase the relative fitness of an organism in its
environment, Adaption; is the accumulation of adaptive traits over time.
- Although evolution has produced all the characteristics of organisms, not all are necessarily adaptive, Some traits
may be the products of chance events and genetic drift. Others are produced by alleles that were selected for
unrelated reasons. Other characteristics result from the action of basic physical laws
13) Describe why there are limits to adaptive evolution (i.e., why organisms can never be perfectly adapted to
their environment). [Comprehension] 17.5B
- Natural selection cannot result in perfectly adapted organisms because adaptive traits represent compromises
among 1) conflicting needs; 2) because most environments are constantly changing 3) and because natural selection
can affect only existing genetic variation
[1) The adaptive traits of most organisms are compromises produced by competing selection pressures ex mates 2)
No organisms can be perfectly adapted to its environment because it changes over time. When selection occurs in a
population, it preserves alleles that are successful under the prevailing environmental conditions. Thus, each
generation is adapted to the environmental condition that their parents lived in (The adaptions will lag behind in next
generation). 3) Another constraint on the evolution of adaptive traits is historical. Natural selection acts on new
mutations and existing genetic variation.]
14) Explain why a character that is strongly influenced by the environment would not respond to selection
(either artificial or natural). [Comprehension]
- If the trait varies within the environment, the trait variations are not genetic (diff alleles), so they cant be selected
for or against ex ph influences flower color strongly cant select for one color over other.
15) 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] 17.3D
- Natural selection exerts little or no effect on traits that appear during an individuals post productive life After
reproductive life, the allele that affects phenotype , whether good or bad, may appear, but it cannot be passed on and
there fore cant be selected. Ex Huntington disease is a dominant allele, but since it appears after 40, it is not selected.
[Huntington's is often "invisible" to natural selection for a very simple reason: it generally does not affect people
until after they've reproduced. This disorder will still be seen in the next generation because individuals don‟t show
symptoms until after they have children (40 years old)]
16) 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. [Comprehension/Analysis] 17.3D
Three modes of natural selection have been identified: 1) Directional Selection, 2) Stabilizing selection, and 3)
Disruptive selection.
1) Stabilizing selection; type of natural selection in which individuals expressing intermediate phenotypes have the
highest relative fitness (By eliminating phenotypic extremes, stabilizing selection reduces genetic and phenotypic
variation and increases the frequency of intermediate phenotypes) Stabilizing selection, affecting many familiar traits
Ex very small or large human newborns are less likely to survive than those born at an intermediate mass.
2) Directional selection; type of natural selection in which individuals near one end of the phenotypic spectrum has
the highest relative fitness. (Directional selection shifts a trait away from the existing mean and toward the favored
extreme. After selection the traits mean value is higher or lower than before) EX predatory fish promote this for large
guppies, since they feed on the smallest guppies in pop. Ex2 Human use this to produce crops and animals with
desired traits.
3) Disruptive selection; type of selection in which individuals with the extreme phenotypes have higher relative fitness than intermediates. (Thus, alleles producing extreme phenotypes become more common, promoting
polymorphism) Ex Galapagos finches, the extreme bill phenotypes appeared to feed efficiently on specific resources
(establishing disruptive selection on size and shape of bill) When drought = strong, When Non drought = small
Disruptive: least common can result in polymorphism increase variability
Directional: common variability may change Value goes up or down
Stabilizing: most common value stays same variability goes down
(polymorphism; is one in which two or more phenotypes are maintained in fairly stable proportions over many
generations.)
17) Identify, given a scenario, which form(s) of natural selection is/are at work. [Analysis]
-Example of Galapagos Finches (beak size). Positive correlation b/w beak size and seed hardness. In dry years,
finches had to eat large, hard seeds and bigger beaks were selected for whereas in wet years, finches could eat small,
soft seeds and smaller beaks were selected for. 1977 drought – birds with deep beaks survived better than shallow
ones but narrow beaks better than wider beaks b/c can concentrate twisting force more efficiently but narrower beaks
didn‟t evolve..why?
18) Predict, given a description, the outcome of a scenario/experiment if selection is acting. [Comprehension,
Analysis, Application]
19) Discuss adaptations, commenting on why: 1) there are limits to adaptation; 2)not all traits are adaptive; 3)
why adaptation is not universally good; 4) adaptations always represent compromises (how an organism’s
phenotype represents a compromise or ‘trade-off’ between the adaptive value of multiple traits.
[Comprehension]
Limits; - not perfect –changes in environment could cause it to be useless – needs existing alleles to work – only
best for options
Not all are adaptive ex products of chance event, genetic drift; produced by alleles selected for unrelated reasons
Always a compromise; May not be perfectly adapted to different trait
20) Provide an example of a fitness trade-off. [Knowledge]
-Fitness trade-off; trade between trait that helps survival in one aspect, and is disadvantageous in another ex long
feather tail – good for attracting mates – bad for escaping predators etc Ex2 Flippers of turtles = advantage for
swimming – Disadvantage= not great when on land laying eggs (embryo cant breathe underwater)
3) MAINTENANCE OF GENETIC VARIATION (HETEROZYGOTE ADVANTAGE, ETC) 18.7
1) Explain why alleles coding for dominant traits don’t, through natural selection, always replace recessive or
rare alleles. [Comprehension, Analysis]
- Because every allele whether dominant or recessive is expressed equally (p2 +q2 = 1).
2) Describe how diploidy can hide harmful recessive alleles from natural (or artificial) selection.
[Comprehension] 17.4 A
- The diploid condition can hide recessive alleles in heterozygotes, with dominate traits masking even deleterious
effects Preserves at low frequencies, especially in large populations
- Diploidy can maintain genetic variation in a population if alleles coding for recessive traits are not expressed in
heterozygotes and are thus hidden from natural selection.
[- The diploid condition reduces the effectiveness of natural selection in eliminating harmful recessive alleles from a
population. Although such alleles are disadvantageous in the homozygous state, they may have little or no effect on
heterozygotes. Thus, recessive alleles can be protected from natural selection by the phenotypic expression of the
dominant allele. In most cases, the masking of recessive alleles in heterozygotes makes it almost impossible to
eliminate - Diploid state preserves recessive alleles at low frequencies in large populations (in small combination
of natural selection and genetic drift can eliminate harmful recessive alleles) The disease state can be hidden
(masked) if it is a recessive phenotype. If natural selection can‟t „see‟ it, then it can‟t be selected against.] 3) Describe how spatial and temporal environmental variability can influence population variation.
[Comprehension, Analysis] ?
-Spatial variation; different alleles exist in different places some are favored over others Ex Camouflage –
Brown coloration in desert vs green coloration in forest
- Temporal variation; different alleles (favored) at different times ex lighter color favored in snowy period
if population spans several different habitats, selection favors different alleles in each of the different habitats,
maintaining population variation (Basically different alleles favored in different environments)
4) Describe heterozygote advantage and frequency-dependent selection. [Comprehension] 17.4B
- A balanced polymorphism; is one in which two or more phenotypes are maintained in fairly stable proportions
over many generations. – Natural section maintains polymorphisms in populations when 1) heterozygotes have
higher relative fitness than both homozygotes, when 2) natural selection occurs in variable environments, 3) or when
the relative fitness of phenotype varies with its frequency in the population
Heterozygote Advantage -A balanced polymorphism can be maintained by heterozygotes advantage; An
evolutionary circumstance in which individuals that are heterozygotes at a particular locus have higher relative
fitness than either homozygote Ex Natural selection preserves the HbS allele in these populations because
heterozygotes in malaria-prone areas have higher relative fitness than homozygotes for the normal HbA; Sickle- cell
anemia in malaria-ridden places Homozygote normal: can carry O2, but can quickly catch malaria, which then
rapidly spreads Homozygote sickle; cant carry O2 Heterozygote: can some what carry O2, but can fight of
parasite since sickle BC release K, which kills and limits spread of malarie
Frequency-Dependent Selection
Frequency-dependent selection; A form of natural selection in which rare phenotypes have a selective advantage
simply because they are rare (have a higher fitness than more common phenotypes) – The rare phenotype will
increase in frequency until it becomes so common that it loses its advantage Ex In predation predators seek out
most common; rare survives. (but eventually that rare becomes the new common)
5) Define neutral selection and neutral variation. [Knowledge] 17.4 C
- Neutral variation; variation in gene sequences that do not affect phenotypic traits of alleles ex change in the 3rd
nucleotide in codon = same amino acid – slightly different proteins may have the same function
- Neutral Selection; selection in which no alleles are favored over others, resulting in them being neither preserved
or eliminated The neutral variation hypothesis explains why large populations and those that have not experienced a
recent bottleneck exhibit the highest levels of genetic variation.(small populations exhibit less variation than large 4) GENE FLOW, GENETIC DRIFT, AND NON-RANDOM MATING.
1) List and define the agents of microevolutionary change: mutation, gene flow, genetic drift (including
founder effect and genetic bottleneck), and natural selection, as well as non-random mating. [Knowledge] 17.3
- The agents of microevolutionary change (;a change in allele frequencies through time, occurs frequently in
natural populations since the restrictive requirements of the model are rarely met) (that violates the Hardy-
Weinberg by changing the populations allele frequency) 1. Mutation; 2. Gene Flow 3. Genetic drift (a.
Population Bottlenecks b. Founders Effect) 4. Natural
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