Population Genetics and Evolution Practice Test (page 3)

Review the following concepts if needed:

• Hardy-Weinberg Equilibrium for Genetics
• Calculating Gene Frequencies for Genetics
• Natural Selection and Evolution for Genetics

Population Genetics and Evolution Practice Test

Vocabulary Questions

For each of the following definitions, give the appropriate term and spell it correctly. Terms are single words unless indicated otherwise.

1. The breeding structure of a population when each gamete has an equal opportunity of uniting with any other gamete from the opposite sex. (One or two words.)
2. The total genetic information possessed by the reproductive members of a population of sexually reproducing organisms. (Two words.)
3. An important model of population genetics. (Three words.)
4. The condition of a locus that does not experience a change in allelic frequencies from one generation to the next.
5. An interbreeding group of organisms sharing a common gene pool. (Two words.)
6. Changes in gene frequencies due to sampling errors in very small populations. (Two words.)
7. A deviation from Hardy-Weinberg expectations at any specific time in a population.
8. A phenotypically and/or geographically distinctive group, composed of individuals inhabiting a defined geographic and/or ecological region, and possessing characteristic phenotypic and gene frequencies that distinguish it from other such groups.
9. The general hallmark criterion that demarcates one biological species from another. (Two words.)
10. Any change in the genetic composition of a population, such as a change in allele frequency.

Multiple-Choice Questions

Choose the one best answer.

For problems 1–4, use the following information. Snapdragon flowers may be red (C^rC^r), pink (C^rC^W), or white (C^WC^W). A sample from a population of these plants contained 80 white, 100 pink, and 20 red-flowered plants.

1. The frequency of the red allele (C^r ) in this sample is   (a) 0.10   (b) 0.20   (c) 0.30   (d) 0.45   (e) none of the above
2. The percentage of pink-flowered plants expected on the basis of the Hardy-Weinberg equation is approximately   (a) 35   (b) 45   (c) 50   (d) 55   (e) none of the above
3. A chi-square test of the sample data against the Hardy-Weinberg expectations produces a chi-square value of   (a) 1.96   (b) 2.43   (c) 2.87   (d) 3.02   (e) 3.11
4. Refer to Table 2-3 to answer this question. Assuming the sample is representative of its population in problem 3 above, it may be said that   (a) the chi-square test is significant and the sampled population is not in genetic equilibrium,   (b) the chi-square test is nonsignificant and the sampled population is not in genetic equilibrium   (c) the chi-square test is significant and the sampled population is in genetic equilibrium   (d) the chi-square test is nonsignificant and the sampled population is in genetic equilibrium   (e) the chi-square value is significant, thereby invalidating the test.

For problems 5–7, use the following information. Black pelage is an autosomal dominant trait in guinea pigs; white is the alternative recessive trait.AHardy-Weinberg population was sampled and found to contain 336 black and 64white individuals.

5. The frequency of the dominant black gene is estimated to be   (a) 0.60   (b) 0.81   (c) 0.50   (d) 0.89   (e) none of the above
6. The percentage of black individuals that is expected to be heterozygous is approximately   (a) 46   (b) 57   (c) 49   (d) 53   (e) none of the above
7. The probability that a black male crossed to a white female would produce a white offspring is approximately   (a) 0.12   (b) 0.14   (c) 0.16   (d) 0.18   (e) none of the above

For problems 8–10, use the following information. Yellow body color in Drosophila is governed by a sex-linked recessive gene; wild-type color is produced by its dominant allele.

8. A sample from a Hardy-Weinberg population contained 1021 wild-type males, 997 wild-type females, and 3 yellow males. The percentage of the gene pool represented by the yellow allele is estimated to be   (a) 0.04   (b) 0.16   (c) 0.21   (d) 0.42   (e) none of the above
9. If the frequency of the yellow allele is 0.01, the percentage of wild-type females expected to carry the yellow allele is   (a) 1.98   (b) 1.67   (c) 2.04   (d) 2.76   (e) none of the above
10. If the frequency of the yellow allele is 1.0 in females and 0 in males, the frequency of that allele in males of the next generation is expected to be   (a) 1.0   (b) 0.5   (c) 0.33   (d) 0.67   (e) none of the above

Hardy-Weinberg Equilibrium Questions

1. At what allelic frequency is the heterozygous genotype (Aa) twice as frequent as the homozygous genotype (aa) in a Hardy-Weinberg population?
2. There is a singular exception to the rule that genetic equilibrium at two independently assorting autosomal loci is attained in a nonequilibrium population only after a number of generations of random mating. Specify the conditions of a population that should reach genotypic equilibrium after a single generation of random mating.
3. Let the frequencies of a pair of autosomal alleles A and a be represented by p_m and q_m in males and by p_f and g_f in females, respectively. Given q_f = 0:6 and q_m = 0:2,   (a) determine the equilibrium gene frequencies in both sexes after one generation of random mating, and   (b) give the genotypic frequencies expected in the second generation of random mating.
4. The autosomal gametic disequilibrium in a population is expressed as d = 0:12. The two loci under consideration recombine with a frequency of 16%. Calculate the disequilibrium (d value) that existed in the gamete pool of   (a) the previous generation, and   (b) the next generation.
5. For two independently assorting loci under Hardy-Weinberg conditions,   (a) what is the maximum value of the disequilibrium coefficient (d)?   (b) Specify the two conditions in which a population must be in order to maximize d.
6. Given gene A at frequency 0.2 and gene B at frequency 0.6, find the equilibrium frequencies of the gametes AB, Ab, aB, and ab.

Calculating Gene Frequencies Questions

Autosomal Loci with Two Alleles Questions

Codominant Autosomal Alleles Questions

7. Apopulation of soybeans is segregating for the colors golden, light green, and dark green produced by the codominant genotypes C^GC^G, C^GC^D, C^DC^D, respectively. A sample from this population contained 2 golden, 36 light green, and 162 dark green. Determine the frequencies of the alleles C^G and C^D.
8. The MN blood group system in humans is governed by a pair of codominant alleles L^M and L^N. A sample of 208 Bedouins in the Syrian Desert was tested for the presence of the M and N antigens and found to contain 119 group M(L^ML^M)), 76 group MN(L^ML^N), and 13 group N (L^NL^N).   (a) Calculate the gene frequencies of L^M and L^N.   (b) If the frequency of L^M = 0:3, how many individuals in a sample of size 500 would be expected to belong to group MN?

Dominant and Recessive Autosomal Alleles Questions

9. The ability of certain people to taste the chemical phenylthiocarbamide (PTC) is governed by a dominant allele T, and the inability to taste PTCby its recessive allele t. If 24% of a population is homozygous taster and 40% is heterozygous taster, what is the frequency of t? (Hint: Use the same method as that employed for codominant alleles for greatest accuracy.)
10. Gene A governs purple stemand its recessive allele a produces green stemin tomatoes; C governs cut-leaf and c produces potato-leaf. If the observations of phenotypes in a sample from a tomato population were 204 purple, cut : 194 purple, potato : 102 green, cut : 100 green, potato, determine the frequency of   (a) the cut allele,   (b) the allele for green stem.
11. An isolated field of corn was found to be segregating for yellow and white endosperm. Yellow is governed by a dominant allele and white by its recessive allele. Arandom sample of 1000 kernels revealed that 910 were yellow. Find the allelic frequency estimates for this population.
12. The R locus controls the production of one system of antigens on the red blood cells of humans. The dominant allele results in Rh-positive individuals, whereas the homozygous recessive condition results in Rh-negative individuals. Consider a population in which 85% of the people are Rh-positive. Assuming the population to be at equilibrium, what is the gene frequency of alleles at this locus?
13. What is the highest frequency possible for a recessive lethal that kills 100% of its bearers when homozygous? What is the genetic constitution of the population when the lethal allele reaches its maximum?
14. Dwarf corn is homozygous recessive for gene d, which constitutes 20% of the gene pool of a population. If two tall corn plants are crossed in this population, what is the probability of a dwarf offspring being produced?
15. A metabolic disease of humans called phenylketonuria is the result of a recessive gene. If the frequency of phenylketonurics is 1/10,000, what is the probability that marriages between normal individuals will produce a diseased child?

Sex-Influenced Traits Questions

16. Baldness is governed by a sex-influenced trait that is dominant in men and recessive in women. In a sample of 10,000 men, 7225 were found to be nonbald. In a sample of women of equivalent size, how many nonbald women are expected?
17. The presence of horns in some breeds of sheep is governed by a sex-influenced gene that is dominant in males and recessive in females. If a sample of 300 female sheep is found to contain 75 horned individuals,   (a) what percentage of the females is expected to be heterozygous,   (b) what percentage of the males is expected to be horned?

Autosomal Loci with Multiple Alleles Questions

18. The genetics of the ABO human blood groups is presented in SOLVED PROBLEM 9.7.   (a) A sample of a human population was blood-grouped and found to contain 23 group AB, 441 group O, 371 group B, and 65 group A. Calculate the allelic frequencies of I^A, I^B, and i.   (b) Given the gene frequencies I^A = 0:36, I^B = 0:20, and i = 0:44, calculate the percentage of the population expected to be of groups A, B, AB, and O.
19. The color of screech owls is under the control of a multiple allelic series: G ^r (red) > gⁱ (intermediate) > g (gray). A sample from a population was analyzed and found to contain 38 red, 144 intermediate, and 18 gray owls. Calculate the allelic frequencies.
20. Several genes of the horse are known to control coat colors. The A locus apparently governs the distribution of pigment in the coat. If the dominant alleles of the other color genes are present, the multiple alleles of the A locus produce the following results: A⁺ = wild-type (Przewalski) horse (bay with zebra markings), A = dark or mealy bay (black mane and tail), a^t = seal brown (almost black with lighter areas), a = recessive black (solid color). The order of dominance is A⁺ > A > a^t > a. If the frequency of A⁺ = 0:4, A = 0:2, a^t = 0:1, and a = 0:3, calculate the equilibrium phenotypic expectations.

Sex-Linked Loci Questions

21. A genetic disease of humans called hemophilia (excessive bleeding) is governed by a sex-linked recessive gene that constitutes 1% of the gametes in the gene pool of a certain population,   (a) What is the expected frequency of hemophilia among men of this population?   (b) What is the expected frequency of hemophilia among women?
22. Color blindness in humans is due to a sex-linked recessive gene. Asurvey of 500 men from a local population revealed that 20 were color blind.   (a) What is the gene frequency of the normal allele in the population?   (b) What percentage of the females in this population would be expected to be normal?
23. The white eyes of Drosophila are due to a sex-linked recessive gene and wild type (red eyes) to its dominant allele. In a Drosophila population the following data were collected: 15white-eyed females, 52white-eyed males, 208 wild-type males, 365 wild-type females (112 of which carried the white allele). Using all the data, calculate the frequency of the white allele.