Terms to know: allele frequency, genotype frequency, Hardy-Weinberg equilibrium, absolute fitness, relative fitness, average population fitness, natural selection, gene, locus, allele, homozygote, heterozygote, genetically dominant, genetically recessive.

Questions:

1. The Hardy-Weinberg Equilibrium model is a model of no evolution.  Why is it important to know this model in order to understand evolution?
2. What are the five assumptions about a population that must be true for the population to be in Hardy-Weinberg Equilibrium?  For each assumption, describe what happens if the assumption is NOT true of a population, and explain why this result occurs.
3. Are the assumptions of Hardy-Weinberg Equilibrium typically met in populations?  Why/why not?
4. In order to model natural selection, the mathematical model of natural selection must be modelling all of Darwin's four postulates.  What are Darwin's four postulates, and how does the mathematical model include each?
5. A population of pocket gophers is in Hardy-Weinberg equilibrium with respect to an enzyme locus, ADH, at which there are two alternate alleles, A1 and A2. The frequency of allele A2 in the population is 0.6.  What are the frequencies in the population of the three possible genotypes at this locus?   Suppose that this population has 13,000 individuals in it (this is a large enough number so that it is effectively infinite, meeting the assumptions of Hardy-Weinberg Equilibrium.)  How many individuals have each genotype?
6. The frequency of a recessive allele at a locus with two alleles in an infinitely large population of spadefoot toads is currently 0.09.  There is no selection at this locus, toads mate at random, this population is completely isolated from all other populations, and no mutations are occurring at this locus.
1.  What will the frequency of the recessive homozygote be in the next generation?
2.  Over a long period of time, what will happen to the frequency of the recessive allele?
7. In house cats, the presence of white splotches is coded for by a dominant allele S; the recessive allele s codes for no white splotches.  In a large feral house cat population, you find that 5/9 of the cats have white splotches.  Assuming random mating, no natural selection on white splotches, and no mutation or gene flow, what proportion of the cats in the population are heterozygous at the S locus?  Will this proportion change from generation to generation? Why /why not?
8. In a randomly mating population of 25,000 (large enough to be considered infinite for the purposes of the assumptions of the models; assume this population size remains constant throughout the generations described in this question) newts there is an enzyme locus with two alleles, F and S, at which the three different genotypes have equal fitness.
1. If the frequency of the FF genotype is currently 0.16, what is the frequency of the SS genotype in this generation?  What will be the frequency of the SS genotype in the next generation?  Assuming the population stays the same size, how many individuals in the next generation will have the SS genotype?
2. In the same newt population, a locus affects the structure of the skin of developing newt larvae as follows:  HH and Hh individuals have skin that resists drying out, while hh individuals have skin that tends to dry out.  Further, Hh and hh individuals have skin that is not harmed by ultraviolet light, while HH individuals have skin that IS harmed by ultraviolet light.  The result is that Hh individuals avoid drying out and are not harmed by ultraviolet light, so that they have the highest fitness.  HH individuals survive 3/4 as well as do Hh individuals; hh individuals survive 1/3 as well as do Hh individuals.  The allele frequency of h at the start of a generation is 0.95.  What will the allele frequency of h be at the start of the next generation?
3. Consider a different newt population.  The conditions are all the same as they were for the population in part (b), except in this population, the allele frequency of h at the start of a generation is 0.05.  What will the allele frequency of h be at the start of the next generation?
4. What do you think will happen to the frequencies of H and h in these newt populations over time (will either become fixed? lost?  will either increase? decrease?).
9. In a population of beavers, three genotypes, BB, Bb, and bb, have different probabilities of survival to reproductive age that result in them having relative fitnesses of .5, .8, and 1.0, respectively. In the gametes that produce one generation, the frequency of B = the frequency of b.  Natural selection resulting from differences in survival to reproductive age is the only form of evolution occurring in this population.
1. What will the allele frequencies of B and b be in the adults of this generation?
2. What will the allele frequencies of B and b be in the gametes that produce the next generation?
3. What will the allele frequencies of B and b be in the adults of the next generation?
4. In the same population of beavers, at the T locus, individuals with the three genotypes TT, Tt, and tt have equal probabilities of surviving and reproduce equally well.  This generation, 90% of the adults have the tt genotype.  What are the allele frequencies of T and t in this population this generation?  What will they be in adults of the next generation?
10. Consider two genes in a large, randomly mating population of turtles with no movement of individuals in and out of the population and no mutation.  The two alleles at one gene, L and M, do not affect fitness.  The two alleles at the other gene, T and t, do affect fitness -- they affect the thickness of turtle shells, and the degree to which they are protected from predation.  TT individuals have thick shells, which repel predators, and survive best.  Tt individuals have medium shell thickness and survive 88% as well as do TT individuals.  tt individuals have thin shells and are easy for predators to eat; they survive only 14% as well as do TT individuals.
1. In a population of ADULT turtles, the frequency of individuals with the MM genotype is 0.06.  Calculate the frequency of individuals with the LM genotype.
2. In a population of gametes at the start of a generation, the frequency of the t allele is 0.23.  Calculate the frequency of zygotes with the Tt genotype.
3. Continuing from part (b), calculate the frequency of the adults that survive from the zygotes that have the Tt genotype.
4. Continuing from part (c), calculate the frequency of the t allele in the gametes that will produce the next generation
11. In a large, randomly mating population of giraffes with no movement of individuals in and out of the population

and no mutation, the two alleles at one gene, A and a, do not affect survival or reproduction of the giraffes.  The two alleles at the other gene, S and B, do affect survival to adulthood by affecting the degree to which giraffes are subject to parasitism by ticks and biting flies.  BB individuals have bitter blood, which repels parasites, and survive best.  SB individuals have neutral tasting blood and survive 80% as well as do BB individuals.  SS individuals have sweet blood and attract parasites; they survive only 4% as well as do BB individuals.
1. In a population of ADULT giraffes, the frequency of individuals with the AA genotype is 0.04.  Calculate the frequency of individuals with the Aa genotype.
2. In a population of gametes at the start of a generation, the frequency of the B allele is 0.14.  Calculate the frequency of zygotes with the SB genotype
3. Continuing from part (b), calculate the frequency of the adults that survive from the zygotes that have the SB genotype.
4. Continuing from part (c), calculate the frequency of the B allele in the gametes that will produce the next generation
12. In a large population of an annual wild pea species, height is controlled by a single locus; HH and Hh individuals are tall, while hh individuals are short.   Because the local environment is very windy, tall plants tend to get broken and survive to reproduce only half as well as well as do short plants.  Mating is random with respect to height and there is no immigration or emigration.In a population of 21,000 (large enough to be considered infinite for the purposed of the Hardy-Weinberg Equilibrium and natural selection models; assume this population size remains constant through the generations described in this question) adult pea plants that successfully reproduce after natural selection through differential survival has occurred, there are 7,000 HH individuals, 7,000 Hh individuals, and 7,000 hh individuals.
1. What will be the frequency of the H allele in the gametes (sperm, in pollen, and ovules) that will unite to make up the next generation?
2. What will be the genotype frequencies of HH, Hh, and hh in the seeds that are formed to start the next generation?  How many seeds will there be with each genotype?
3. What will be the genotype frequencies of HH, Hh, and hh in the adults that develop from these seeds and survive to reproduce?  How many adults will there be with each genotype?
4. Over a long period of time, what do you expect to happen to the H and h alleles in this population?
13. A large population of grass occurs in an area with two distinct kinds of soil.  Some patches of soil contain heavy metal ions, others do not.  The genotypes at the S locus determine how well grass plants survive in the different soil types: SS individuals survive best in heavy metal soils, ss individuals survive best in normal soils, and Ss individuals do not survive very well in either soil.  Grass seeds are dispersed by the wind to different soil types; because normal soil is most common, ss individuals have the highest survival, and a relative fitness of 1.  SS individuals survive next best, having a relative fitness of .75.  Ss individuals have a relative fitness of .25.
1. In this population of grass, the allele frequency of S at the start of a generation is 1/2.  What will the allele frequency of S be at the start of the next generation?
2. In a different large population of grass, the fitnesses of the SS, Ss, and ss genotypes are the same as in the first population.  However, in this population, the allele frequency of S at the start of a generation is 0.90.  What will the allele frequency of S be at the start of the next generation?
3. What do you think will happen to S over time in the first population?  Will the same thing happen in the second population?  Why/ why not?
14. In a very large population of crayfish in a cold, mountain stream, there are two possible alleles at the locus of enzyme D.  One form of this enzyme, coded for by allele D, functions more effectively at cold temperatures than does the alternate form, d.  As a result, DD and Dd individuals survive better than do dd individuals; the absolute fitness of DD and Dd is 3, the absolute fitness of dd is 2/3.  This population is isolated from other populations; individuals mate at random with respect to the D locus. In a population of 10000 fertilized crayfish eggs, there are 2000 dd individuals.
1. What is the frequency of D in the fertilized egg population?
2. What are the relative fitnesses of the three possible genotypes?
3. What is the frequency of D expected to be in the population of gametes produced by this population of fertilized eggs (once they grow up and reproduce).
15. Go back over each of the questions in this section in which natural selection was modeled and identify the mode of selection as one of the following: dominant has highest fitness, recessive has highest fitness, fitness codominance, heterosis (overdominance), or underdominance (negative heterosis)