Lewis/Life - Answers to End-of-Chapter Questions

Chapter 20 - Answers to End-of-Chapter Questions

TO REVIEW

1. Definitions in text.

2. See the Hints Related to Specific Chapter Topics Section III above.

3. Both constitute changes in a given gene pool.

4. Answers will vary.

5. Answers will vary but should include a statement about the chances for two people to inherit the same recessive allele. Also, some students might question whether deleterious is necessary lethal. Sometimes there are compensating mechanisms. As mentioned in the text, humans use eyeglasses.

If you would like to work this out mathematically, look at the gene for one form of hemophilia, which occurs at the rate of 1/10,000 alleles. Every indication is that this rate has remained quite constant (until today when we have methods of helping hemophiliacs live a normal life). Plug this 1/10,000 into the Hardy-Weinberg equation. Assume the homozygous recessive is lethal. Run the numbers through several generations. What happens to the heterozygote numbers? (If 1/10,000 is too large a number, substitute any number; the results will be the same. If all other conditions are constant, the gene will not fall out of the population.)

6. A niche was opened. Directional selection favored one form of the moth; after pollution diminished, directional selection favored the other form. Directional selection favored the antibiotic-resistant forms of Mycobacterium tuberculosis.

7. Definitions in text.

8. Definition in text.

9. Geographic isolation followed by reproductive isolation.

10. Premating = obstacles prevent individuals from mating. Postmating = obstacles prevent the production of fertile offspring.

11. Students may have different interpretations of this question. In a global sense, the answer could be "environmental or genetic changes." In the reproductive sense, the answer could be "reproductive isolation or genetic changes." (Environmental change and reproductive isolation are not necessarily the synonymous.) Other answers may be possible.

12. Definitions in text.

13. Niches are available; food is available; predators have disappeared.

14. Answers will vary.

15. Gamete. Only the gametes are passed on to the next generation.

TO THINK ABOUT

1a. Assuming the illness is recessive, this will cause a shift toward the dominant.
b. The exact mathematical impact would depend on a number of factors. In general, however, the gene pool for the common alleles would increase.
c. Within the Amish community, assuming the members abided by the rule, Hardy-Weinberg equilibrium would not be disrupted.
d. There would be a shift away from that blood type. To figure out the exact impact, more information would be needed.

2a. They may be descended from a particular group that came to North America from Asia.
b. They may be related to "Arnold."
c. Increased allele frequency due to selective gene pool. Ellis-van Creveld syndrome.
d. Population bottleneck causing poor sperm quality and high newborn death rate.
e. Heterozygote superiority. (Prize-winning genes are not necessarily healthy!)
f. Population bottleneck resulting from a typhoon.

3. Stabilizing selection.

4a. 0.4
b. 0.6
c. 48
d. 16
e. 36

Start with p + q = 1
Since there are 16 gray fraggles, and since gray is recessive, 16 must equal q2 and q must equal 4.
Therefore, p + 0.4 = 1. So, p = 0.6.

Plug into the expanded equation:
0.36 + 0.48 + 0.16 = 1

5. Since the population of the green fraggles will be decreased, the number of green fur alleles will also decrease. The population will shift toward the gray.

6a. Bottleneck (or founder effect)
b. Directional shift (other answers possible)
c. Could be directional selection but other answers are possible. Someone might say punctuated equilibrium! With the information given, however, we are not certain if postmating reproductive isolation has occurred.
d. Extinction

7. The traits often bring deleterious side-effects.

8. Answers will vary, though most students will include something about "directed molecular evolution" as not being natural.

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