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natural selection

BIOL 4 Homework #3

Short Answer

1. A gene 1,440 is base pairs long and codes for an enzyme composed of only 192 amino acids. Discuss why this discrepancy might exist.

2. Errors in transcription occur about 100,000 times as often as errors in DNA replication. Why can this high rate be tolerated in RNA synthesis, but not DNA synthesis?

3. A number of efforts are underway to identify human genetic polymorphisms that correlate with multifactorial diseases such as diabetes, heart disease, and cancer. What would be the uses of such information? What concerns do you think there might be about this kind of testing?

4. In what ways is artificial selection different from natural selection? Darwin used his knowledge of artificial selection extensively to develop and support his arguments for evolution via natural selection. Was this a wise choice?

5. In a population with 600 members, the numbers of individuals of three different genotypes are AA = 350, Aa = 100, aa = 150.

a. What are the genotype frequencies in this population?

1. AA =

2. Aa =

3. aa =

b. What are the allele frequencies in this population?

1. A =

2. a =

c. What would be the expected genotype frequencies if this population were in genetic equilibrium?

1. AA =

2. Aa =

3. aa =

d. Is this population in genetic equilibrium? Explain.

6. As human life expectancy increases, many people face degenerative conditions such as Alzheimer’s disease that are (primarily) linked to advancing age. Assuming that some individuals may be genetically predisposed to successfully combat these conditions, is it likely that natural selection alone would favor such individuals? Why/why not?

Multiple Choice

1. Which statement about complementary base pairing is NOT true?

a. it plays a role in DNA replication b. in DNA, T pairs with A

c. the base pairs are of equal length d. purines pair with purines, and pyrimidines pair with pyrimidines

2. The role of DNA ligase in DNA replication is to:

a. add more nucleotides to the growing strand one at a time

b. open up the two DNA strands to expose template strands

c. remove incorrectly paired bases

d. bond Okazaki fragments to one another

3. The polymerase chain reaction (PCR):

a. is a method for sequencing DNA b. is used to transcribe specific genes

c. does not require DNA replication primers d. amplifies specific DNA sequences

4. An mRNA has the sequence 5-AUGAAAUCCUAG-3. What is the template DNA strand sequence?



5. Transcription:

a. produces only mRNA b. requires ribosomes

c. takes place only in eukaryotes d. produces RNA growing from the 5 to 3 end

6. The adapters that allow translation of the 4-letter nucleic acid language into the 20-letter protein language are called:

a. transfer RNAs b. ribosomal RNAs

c. messenger RNAs d. ribosomes

7. The genetic code:

a. differs for prokaryotes and eukaryotes b. has changed over the course of evolution

c. has multiple codons for some amino acids d. is ambiguous

8. Control of gene expression in eukaryotes includes all of the following except:

a. alternative RNA splicing b. stabilizing of mRNA by miRNA

c. binding of proteins to DNA d. transcription factors

9. In undisturbed strata of sedimentary rock, the oldest rocks are:

a. found at the top b. found at the bottom

c. found in the middle d. randomly distributed

10. The concentration of oxygen in Earth’s atmosphere:

a. has increased steadily through time b. has decreased steadily through time

c. was at its highest levels in the Cambrian d. has been both higher & lower than current levels

11. 14C can be used to determine the ages of fossil organisms because:

a. all organisms contain many carbon compounds

b. 14C has a regular rate of decay to 14N

c. the ratio of 14C to 12C in living organisms is always the same as that in the atmosphere

d. all of the above

12. The appropriate unit for defining and measuring genetic variation is the:

a. cell b. individual

c. population d. community

13. Which of the following is true?

a. Wallace proposed a theory of evolution by natural selection that was similar to Darwin’s

b. Malthus claimed that because human population growth would outstrip any increases in food production, famine was a likely result

c. Darwin realized that all populations had the capacity to rapidly increase in numbers

d. all of the above

14. Which of the following is NOT required for a population in Hardy-Weinberg equilibrium?

a. no migration between populations b. no natural selection acting on populations

c. mating is random d. multiple alleles at every locus

15. Disruptive selection maintains a bimodal distribution of bill size in a population of seed eating birds because:

a. bills of intermediate shapes are difficult to form

b. the birds two major food sources differ significantly in size and hardness

c. males use their large bills in displays

d. older birds need larger bills than younger birds

16. The fitness of a genotype is a function of the:

a. average rate of survival and reproduction of individuals with that genotype

b. individuals that have the highest rates of both survival and reproduction

c. average reproductive rate of individuals with that genotype

d. individuals that have the highest rates of reproduction

17. A species of flowering plant lives only one year and can produce red, white, or pink flowers, depending on its genotype. There are 300 red-flowering, 500 white-flowering, and 800 pink-flowering plants in a population. The following year, 600 red-flowering, 900 white-flowering, and 1,000 pink-flowering plants are observed. Which color has the highest fitness?

a. red b. white

c. pink d. cannot be determined

18. Ability to taste PTC (phenylthiocarbamide) is determined by a dominant allele T, with tasters having the genotypes Tt or TT and nontasters having tt. If 36% of the members of a population cannot taste PTC, then according to Hardy–Weinberg, the frequency of the T allele should be

a. 0.36 b. 0.4

c. 0.6 d. 0.64

19. A gene in humans has two alleles, M and N, that code for different surface proteins on red blood cells. If you know that the frequency of allele M is 0.2, according to the Hardy–Weinberg rule, the frequency of the genotype MN in the population should be

a. 0.16 b. 0.2

c. 0.64 d. 0.8

20. Long-horned cattle have greater difficulty moving through heavily forested areas compared with short-horned cattle, but long-horn cattle are better able to defend their young against predators. This contrast is an example of:

a. an adaptation b. genetic drift

c. natural selection d. a trade-off

21. Which of the following is NOT a condition expected to favor allopatric speciation?

a. continents drift apart and separate previously connected lineages

b. different environments on two sides of a barrier cause populations to diverge

c. the range of a species is separated by loss of intermediate habitat

d. tetraploid individuals arise in one part of the range of a species

22. Which of the following is NOT a potential prezygotic reproductive barrier?

a. temporal segregation of breeding seasons b. differences in chemicals that attract mates

c. hybrid infertility d. spatial segregation of mating sites

23. Which statement about speciation is NOT true?

a. it always takes thousands of years b. in animals a physical barrier is common

c. in plants it often results from polyploidy d. it has produced modern diversity levels

24. Which of the following would you expect to have higher rates of speciation?

a. sexually dimorphic birds compared to sexually monomorphic birds

b. insects with specialized diets compared to insects with generalized diets

c. plants with animal pollination compared with plants with wind pollination

d. all of the above


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