Question

10. Consider the simplified scenario for genetic determinants of height in humans, where there are three genes (A/B/C) with varying numbers of alleles (3/3/2) affecting height, and with different effects in males and females. (Assume additive contributions, thus the effect of having genotype A1A2 is +0.1” + +0.2” = +0.3”). Average height for men and women is 69” and 64”.

Gene	Allele	Male(effect	Female(effect
A	1	+0.1	+0.1
	2	+0.2	+0.2
	3	41.3	41.5
B	1	+0.5	+.3
	2	40.4	40.2
	3	40.1	40.1
C	1	42	+1.5
	2	+0.1	0

What is the expected height for a male with genotype A2A2B1B3C1C2 (3 points)?

11. Consider a cross between two heterozygotes.
What is the probability that their first offspring has recessive phenotype? (2 points)

What is the probability that their first offspring has recessive phenotype and the second offspring also has the recessive phenotype? (2 points)

What is the probability that out of their first offspring, one has dominant phenotype and one has recessive phenotype? (2 points)

15. The gene for petal color in a flower has incomplete dominance, so that individuals with two A1 alleles (A1A1) are black, individuals with two A2 alleles (A2A2) are white, and individuals with one of each allele (A1A2) are mottled.

In a cross between two black flowers, what is the probability of getting a mottled offspring? (2 points)

3"      4"

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1"      2"

                          

In a cross between a black flower and a mottled flower, what is the probability of getting a black offspring? (2 points)

In a cross between two mottled flowers, if there are two offspring, what is the probability of getting one black offspring and one mottled offspring? (2 points)

In a cross between two mottled flowers, if there are two offspring, what is the probability of getting one white offspring and one mottled offspring? (2 points)

In a cross between two mottled flowers, if there are nine offspring, what is the probability of getting exactly three mottled offspring? (2 points)

16. Two individuals that are heterozygous for a recessive autosomal trait have an offspring with dominant phenotype. What is the probability that that offspring is a carrier (heterozygote?) (3 points)

If that offspring has an offspring with an individual with the recessive condition, what is the chance their offspring has the condition? (2 points)

17. Most randomly occurring mutations that occur in humans do not have an effect on phenotype. Why is this? (4 points)

18. Imagine that coronavirus has a 0.002% incidence in the population. A test for the virus has a 0.001% false positive rate and no false negative rate (false positive rate means the chance that if an uninfected individual takes the test the test will falsely identify them as infected). If a random person takes the test and gets a positive result, what is the chance that they are infected? (Show your work to earn partial credit) (4 points)

Now consider the case in the future, where the incidence of the virus has increased to 1%. Now if a random person takes the test and gets a positive result, what is the chance that they are infected? (2 points)

19. Your colleague is studying long toes in the California vole (Microtus californicus). She proposes that this trait is due to to an X-linked dominant allele.

You go for a hike in Oakland, and notice that very few of the California voles you see have the long toe trait. Does this affect your colleague’s hypothesis? How? Why? (2 points)

You go for a walk in Golden Gate Park, and notice that, among California voles in the Golden Gate population, females are much less likely than males to have the long toe trait. Does this affect your colleague’s hypothesis? How? Why? (2 points)

20. You are a genetic counseler. A mother and father with a son and a daughter come to see you. The mother and the father both have a very rare condition that no one has ever studied, but neither their son or their daugther does. Karyotype analysis shows that the mother and the daugther are XX and the father and the son are XY. You think about it and realize that this pattern cannot be due to a number of simple inheritance patterns. Explain why:

Why can’t it be an autosomal dominant condition? (2 points) Why can’t it be Y-linked condition? (2 points)
Why can’t it be an X-linked dominant condition? (2 points) Why can’t it be an X-linked recessive condition? (2 points) Why can’t it be a mitochondrial condition? (2 points)

Answer 1