Question

Problem 5-35: Two genes control color in corn snakes as follows: O- B- snakes are brown, O- bb are orange, oo B- are black, and oo bb are albino. An orange snake was mated to a black snake, and a large number of F1 progeny were obtained, all of which were brown. When the F1 snakes were mated to one another, they produced 100 brown offspring, 25 orange, 22 black, and 13 albino. a. What are the genotypes of the F1 snakes? (1 point) b. What proportions of the different colors would have been expected among the F2 snakes if the two loci assort independently? (1 point) c. Do the observed results differ significantly from what was expected, assuming independent assortment is occurring? What is the probability that differences this great between observed and expected values would happen by chance? (3 points)

Answer 1

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Answer 2

For the two genes:

• a. F1 snakes have genotypes O- B-.
• b. If loci assort independently, F2 proportions depend on possible gametes (OB, Ob, oB, ob).
• c. Conducting a chi-square test compares observed and expected values to assess independence, determining if differences are significant.

What are these genes control color?

a. The genotypes of the F1 snakes can be determined based on the color phenotypes observed. Since all F1 offspring are brown, the parental snakes must be heterozygous at both loci. Therefore, the genotypes of the F1 snakes are O- B-.

b. If the two loci assort independently, the possible gametes produced by the F1 snakes are OB, Ob, oB, and ob. The expected proportions among the F2 snakes would be determined by combining these gametes, resulting in various genotypes and color phenotypes.

c. To assess whether the observed results differ significantly from expectations, a chi-square test can be conducted. The observed and expected values for each color phenotype are compared, and the probability of obtaining differences as great as those observed is calculated. If the probability is below a chosen significance level (e.g., 0.05), it suggests that the differences are significant, and independent assortment may not be occurring as expected.