1. d.
2. e.
3. The rarer allele occurs primarily in the low fitness heterozygote and is therefore lost
4. c.
5. Only homozygotes for the allele leading to best fitness have highest fitness; the other allele always leads to lower fitness so it is lost
6. a.

(7-9 can be in any order)

7. The differences in claw length are genetic
8.  More individuals are born than survive to reproduce each generation
9. Individuals with certain claw lengths have higher fitness than others

10. c.
11. a
12. a.
13. b.
14. a.
15. d.
16. b.
17. a.
18. local adaptation
19. c.
20. The traits that evolve are those that increase survival and reproduction of individuals, not species

21.   (a) Freq(t)=q=Freq(tt)+(1/2)Freq(Tt) = 0.04 + (1/2)(0.66) = 0.37

        Freq(tt) = q^2 = 0.37^2 = 0.14

(b)  Freq(tt) in zygotes = 0.36= q^2        Freq(t)= square root of 0.36 = 0.6 = q        Freq(T)= 1-0.6=0.4=p

        wTT = 1        wTt=1        wtt = 0.3

    wbar = (0.4)^2(1) + (2)(0.4)(0.6)(1) + (0.6)^2(0.3) = 0.75

    Freq(tt) = (0.6)^2(0.3)/0.75 = 0.14

(c) Line A: should start low and be lost (reach zero)
      Line B: should start low and remain low but not be lost (never reach zero)

22. A. Buri set up a large number of small fruit fly populations in identical conditions; each initially had half one eye color and half an alternate eye color allele.  Since conditions were identical, if they evolved through natural selection, the same allele would become fixed or common in each population.  Genetic drift predicts that the allele that gets fixed is determined randomly, so that half the time one would be fixed and half the time the other would be fixed.  Since his results were that an allele was fixed, and about half the time it was one allele and half the time the other, genetic drift was apparently occurring.

B. On island habitats they found by marking and recapturing snakes of both colors that unbanded snakes survived better than banded; this was apparently because of lower predation on unbanded snakes.  On the mainland, most snakes are banded.  If gene flow were the only form of evolution occurring, island populations would have a mixture of banded and unbanded snakes because of movement of banded snakes from the mainland; the mixture would end up being the same as on the mainland so most snakes would be banded.  If natural selection were the only form of evolution occurring, island populations would end up with all unbanded snakes, since banded have lower fitness.  The observed populations on islands have mostly unbanded snakes but a low frequency of banded snakes, indicating that natural selection is the main form of evolution but that there is also some gene flow keeping banded snakes in the population

C.  The researchers studied genetic variation among populations.  Genetic drift will create high genetic variation among populations by chance; gene flow will create low genetic variation among populations because individuals moving among populations make the different populations similar genetically.  They could age the islands because they rise from the water at a constant rate.  Young islands with young campion populations would be small and predicted to have high genetic drift since genetic drift has more impact on small populations.  Medium aged populations would be larger and show less drift; pollen and seed movement to and from such populations would be predicted to create high gene flow.  Old populations are in the process of dying out, so they become small and should show high genetic drift again.  As predicted, young and old populations showed high levels of genetic variation among populations while medium aged showed little variation among populations, so drift was apparently affecting young and old populations most strongly and gene flow was affecting medium aged populations.

23. NOTE: If you answered the question written on the test (when instructed not to), you lost 4 points automatically but could still receive up to 10 points if your answer for that question was correct.  If the few of you who did this have questions about your answer, please see me.  The answer given here is to the questions about which form of natural selection would maintain a constant 5% frequency of a low fitness homozygote.

Heterosis would maintain the genetic deformity in a constant frequency of 5% because reproduction by the heterozygotes maintains both alleles in the population, since the heterozygote contains both alleles.  As a result, both homozygotes, which have lower fitness, are produced by reproduction of these alleles when the heterozygotes reproduce, so the alleles reach constant frequencies at equilibrium and constant proportions of the three genotypes would be produced.

Dominant having highest fitness would not maintain a genetic deformity in a frequency as high as 5%.  It does maintain both alleles, but the recessive becomes extremely rare because when it is produced it has low fitness so the allele declines in frequency, so if 5% were produced one generation the frequency would go down, it would not remain constant.  The frequency of the recessive allele after many generations will be so low that it occurs almost entirely in heterozygotes, so there would not be anywhere near as many as 5% of the individuals produced with the recessive homozygous condition.

Fitness codominance, recessive having highest fitness, and underdominance all result in an allele being lost, so all individuals would have the same phenotype and high fitness. None of these, as a result, would have 5% of the individuals with a low fitness genotype. For fitness codominance and recessive having highest fitness, this occurs because individuals with even one of the alleles that leads to the low fitness homozygote has lower fitness than the high fitness homozygote -- all individuals with the "bad" allele thus have lower fitness so it will be lost.  For underdominance this occurs because the heterozygote has low fitness and the rare allele will occur primarily in the heterozygote and will thus be lost.