Key to Exam 3
1. b.
2. d.
3. a.
4. convergent evolution
5. von Baer's Law
6. d.
7. the outgroup (primitive state) proceeds farther in development than does the derived state
8. no
9. b.
10. higher rate of speciation after evolution of key innovation
11. they occur next to each other on chromosomes
12. d. (however, credit may have been given for other answers depending on your explanation in question 13.)
13. proteins coded by several genes determine length of time of elongation of limb segments so changing this could change the rate of development (credit was also given if you made a convincing, clear case for one of the other choices from 12.)
14. c.
15. a. (note that b is based on species selection and may explain the large number of species with sexual reproduction but does NOT explain why sexual reproduction evolves within species.)
16. should be a plot of offspring shell length (trait value) versus mid-parent shell length (trait value) with a line sloping upward at about 45 degrees.
17. c.
18. (0.5)2(0.6) + (2)(0.5)(0.5)(0.6) + (0.5)2(1)
19. a.
20. d.
21. A mass extinction is an event during which many species from many distantly related groups die off, leaving no descendents, in a short period of time. Adaptive radiation occurs after mass extinctions. Adaptive radiation occurs when there is potential for many species to evolve to use the environment in many different ways because of few competing species; after a mass extinction there are few competing species so adaptive radiation can occur then.
22. (a) Traits being weighted equally means that each trait had the same impact on determining the best phylogeny as did each other trait. This could be a good thing since it does not bias the analysis ahead of time toward any particular tree. This could be a bad thing because transitions occur more frequently and are more subject to chance convergence, so the phylogeny might be more accurate if transitions were weighted less than transversions.
(b) Bootstrap analysis refers to computer based random re-sampling of the data used to make the phylogeny to create many new datasets based on the original data (but with some characters randomly repeated more than others.) It is useful because it allows one to evaluate support for each individual branch in the phylogeny (the more times a branch occurs in a phylogeny based on the bootstrap-produced datasets, the more likely it is to be real.)
(c) A heuristic search is a method of finding well-supported phylogenies for large numbers of species and characters where it is not feasible to check all different phylogenies to see which is best. The problem is that it is not guaranteed to find the best phylogeny; it is more likely to find it if it is repeated from different initial starting trees so that the initial tree does not have as strong an effect on the final phylogeny that it finds.
23. (a) They evolved through sexual selection. Sexual selection typically results in the evolution of traits like horns and bright coloration in males, but not females, because females put so much time and energy into producing offspring that they can not increase the number of offspring they have much by having many mates, but males reproduction is not limited by the energy of producing offspring and they can increase the number of offspring they have by having more mates, so traits that attract more mates or allow better competition for mates evolve in males, not females.
(b) Honest advertisement: bright color indicates the quality of the male; males with bright color either provide direct benefits such as being better providers of parental care, or indirect benefits such as high quality genes that the offspring will inherit. Sensory exploitation: the bright colors of the male stimulate the sensory receptors in the eyes of the females more than would other colors so males with bright colors are more noticeable and therefore chosen by females. Runaway sexual selection: initially there is random variation in male coloration and female preference; when females who prefer brightly colored males mate with those males their offspring inherit both the alleles for bright color and the alleles for preference for bright color so these traits become genetically correlated within individuals. When individuals with this genetic correlation mate, offspring are even more brightly colored since they inherit bright color from both parents and have an even stronger preference for bright color since they inherit preference alleles from both parents. This process continues until genetic variation is lost or until there is such strong natural selection against bright color that it balances sexual selection for bright color.
24. (a) Haplodiploidy results in increased relatedness (r) between the altruist and the recipient of altruism, if altruist and recipient are full sisters, because they inherit half of their genes in common from their father, since he is haploid and all his sperm are identical, plus an additional 1/4 in common from their mother, so they have a relatedness of 3/4. Thus, if the recipient of altruism is the full sister of the altruist there is a high probability that she will carry the allele for altruism, and therefore it can be passed to the next generation.
(b) Many answers are possible as long as they are based on b, the increase in offspring number that the recipient of altruism has as a result of receiving help from the altruist, or c, the number of offspring the altruism does NOT have as a result of being an altruist. For example, if resources for reproduction, such as food, are scarce, then it is likely that b will be increased because with help gathering food the recipient of altruism would have many more offspring.