IMPORTANT NOTES:
1. fitness
2. Hardy-Weinberg Equilibrium
3. gene flow
4. genetic drift
5. heritability
6. stabilizing selection [note: many of you said "heterosis"; this is not correct because the questions specifies that this is a quantitative (polygenic) trait and the intermediate phenotype for such a trait is NOT necessarily coded for as a heterozygous form.]
7. c.
8.
9. b.
10. a.
11. Any question about how a human structure evolved or how humans are related to other species is correct (examples: "How did the large human brain evolve?" "Did humans and chimpanzees evolve from a common ancestor")
12. a.
13. Any of the following reasons: All species come from a common ancestor so they've been evolving the same length of time, all species have some traits that are primitive and some that are derived so the whole species can't be considered primitive or derived, species have adaptations to their own environments.
14. b.
15. b.
16. Enough gene flow to maintain some genetic variation so natural selection can occur; not so much that populations become just like populations from other areas
17. d.
18.
19. Early in their history, most giraffes had short necks but a few, through genetic mutations, had longer necks -- thus, there was variation in neck length among individuals and the differences among individuals were genetic. Not all giraffes born each generation survived to reproduce. Because their longer necks let them obtain food from trees, long necked giraffes survived to reproduce better than did short necked giraffes. As a result, long neck giraffes reproduced more, so more alleles for long necks were passed on from generation to generation than were alleles for short necks, and over time all giraffes came to have long necks.
20.
(a) d.
(b)
Freq(B)=Freq(BB)+ (1/2)Freq(Bb)=0.7+(1/2)(0.2)=0.8
Freq(b)=1-Freq(B)=1-0.8=0.2
(c) genotype frequencies of zygotes are in Hardy-Weinberg
Proportions, so:
Freq(S)=square root of Freq(SS) = square root of 0.36=0.6=q
Freq(B)=1-Freq(S)=1-0.6=0.4=p
wbar=(0.4)2(1)+2(0.4)(0.6)(0.9)+(0.6)2(0.2)=
0.16+0.432+0.072=0.664
Freq(SS)=(0.072)/0.664=0.11
21.
Freq(L)=[2(100)+40]/(2)(150)=0.8
Freq(l)=1-0.8=0.2
Expected numbers:
LL: (150)(0.8)2=96
Ll: (150)(2)(.8)(.2)=48
ll: (150)(0.2) 2 = 6
chi-square=(100-96) 2/96 + (40-48) 2/48 +
(10-6) 2/6 = 0.17+1.33+2.67=4.17
4.17>3.841 so the population is not in Hardy-Weinberg proportions;
natural selection is likely.
22.
(i) The near universality of the genetic code refers to the fact that the sets of three DNA and RNA bases that provide information for the amino acids that make up proteins are the same (with very few minor exceptions) in all life. This suggests that all life came from one ancestor because there is no apparent chemical reason for the code to be the same so the most likely explanation is that all life had one ancestor which had this genetic code and all life has inherited that genetic code from the ancestor to all life.
(ii) The hierarchical pattern of homology refers to the fact that large groups of species all have some common traits and can be subdivided into smaller and smaller groups with more and more traits in common. This suggests that species have evolved from common ancestral species (through speciation) because the most likely explanation for this pattern is that species have traits in common because they inherited them from ancestral species with those traits; close relatives thus have many traits in common and distant relatives fewer traits in common.
(iii) Vestigial organs are structures that are similar to structures found in other species but very reduced in size and sometimes without apparent function. They provide evidence that species have evolved, through speciation, from common ancestral species because the most likely explanation for the existance of these small, apparently functionless structures is that they were inherited from an ancestor which, like other species that currently have the structure, had these structures in large, functional form.
(iv) Ring species are species with a circular geographic distribution; individuals from neighboring populations can interbreed except at one point where they are too different to interbreed. The existence of ring species suggests that speciation is possible because within these ring species some forms are so different that they can't reproduce so it appears that within a species it is possible for populations to evolve to be as different as are different species (that is, unable to reproduce.)
23. (i) Buri tested the hypothesis that eye color in fruit flies evolved through genetic drift. He set up many small populations, each consisting of fruit flies with half one eye color allele and half another eye color allele. The genetic drift hypothesis predicts that one eye color allele will be fixed in each population but that the allele fixed will be random, so that in approximately half the populations one allele should be fixed and in the other half, the other allele should be fixed. This is what Buri observed, so the hypothesis of genetic drift is supported.
(ii) King tested the hypothesis that color of water snakes on islands was affected by gene flow from the mainland. The gene flow hypothesis predicts that banded and unbanded snakes will occur on the island (since through natural selection island snakes should be unbanded, since unbanded snakes survived better on the island.) King found a small number of intermediately banded snakes on the islands suggesting that some gene flow occurs, although not at a high rate since most snakes were banded.
(iii) Giles and Goudet tested the hypotheses that genetic drift affected small island populations and that larger populations were affected more by gene flow. They predicted that since young and old populations were both small, there should be high genetic variation among young and old populations caused by genetic drift, but that since intermediate age populations were larger and had more dispersing individuals that gene flow should result in genetic similarities among populations. This is what they observed, so both hypotheses are supported.
24. Heterosis maintains most genetic variation because heterozygotes have highest fitness, meaning that most reproduction is by heterozygotes. Since heterozygotes contain both alleles, they reproduce both alleles each generation, so both alleles are maintained in the population which means there is high genetic variation. Natural selection in which the dominant has highest fitness results in low genetic variation because the dominant allele increases in frequency until it is almost fixed; a few recessive alleles remain in the population because they occur in heterozygotes which are identical in phenotype to dominant homozygotes and therefore reproduce just as well, but this number is very low since if there were many heterozygotes, some recessive homozygotes would be produced and these would be selected against. Natural selection when the recessive has highest fitness results in no genetic variation; all individuals with the dominant allele have low fitness so the dominant allele becomes lost, the recessive allele becomes fixed, so genetic variation is lost. When underdominance occurs, the allele that is less common to start out occurs primarily in heterozygotes. Since heterozygotes have low fitness, this less common allele becomes progressively less and less common as heterozygotes die out. The allele that was initially more common thus becomes fixed, so genetic variation is lost.