Courses.washington.edu_gs361win_problems_PS3-2 %28Genome 361 Winter 2012%29

Genome 361 Winter 2012 PS3-2: Mendelian Genetics

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Mendelian Genetics and Probability Homework – Part II 1. Below is a pedigree in which some members of the family have hemophilia, which is caused by mutations in the Factor VIII gene, located on the X chromosome.

Melissa and her husband Jeff (who does not have hemophilia) just found out they are pregnant (and cousins ☺). What is the chance their child will have hemophilia? A. 0% B. 25% C. 25% if boy, 0% if girl D. 50% E. 50% if boy, 0% if girl 2. In sexually reproducing organisms, which of the following is TRUE about how many of a son’s body cells (any cell in the body except a sex cell or a red blood cell) contain DNA from his mother? A. A little less than 50% of a son’s body cells contain some DNA from his mother. B. 50% of a son’s body cells contain some DNA from his mother. C. A little more than 50% of a son’s body cells contain some DNA from his mother. D. 100% of a son’s body cells contain some DNA from his mother.

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3. In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A lethal recessive allele that causes death of the embryo occurs on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male heterozygous for the lethal allele and a normal female? A. 2:1 male to female B. 1:2 male to female C. 1:1 male to female D. 4:3 male to female E. 3:1 male to female 4. Menkes Syndrome is a rare X-linked disease that affects copper metabolism. Treatment with copper injections may improve the life of a person with Menkes disease but there is no newborn screening for this disorder. Most children born with this disease die before they turn 10. Lawrence and Natasha have 2 sons: Cale and Reid. Cale has Menkes Syndrome. Cale inherited the mutation in the MK gene that causes Menkes Syndrome from: A. His mother B. His father C. Both parents D. Could be either parent – it cannot be determined. 5. What is the probability that Reid is a carrier for Menkes Syndrome? A. 0% B. 25% C. 50% D. 75% E. 100%


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6. You are studying fruit flies that have a metabolic disorder. An enzyme assay is available to determine the level of the enzyme in tested flies. Flies that are EE are scored as 1.0 (100% activity), flies that are Ee are scored as 0.5 (50% activity), and flies that are ee are scored as 0.0 (0% activity). Two Ee flies mate and you test the enzyme activity of all of their progeny. Here are the results: Number of flies Enzyme activity 29 1.0 68 0.5 23 0.0 (i). For this cross, how many flies do you expect would have an enzyme activity of 0.5? (ii). How many degrees of freedom are there? (iii). What is your χ2 statistic and conclusion for this analysis? Refer to the χ2 table in your quiz section 3 handout to look up the P-value. You will be given a χ2 table on the exam. 7. In Drosophila, the mutant allele b causing brown eyes is temperature sensitive. In flies grown at 29ºC the mutant allele is dominant, but in flies grown at 22ºC the mutant allele is recessive. In other words, a Bb fly grown at 29ºC is brown-eyed, but a Bb fly grown at 22ºC is red-eyed. Denote the wild type allele for red eyes as B. The following cross is performed: Bb x Bb (i) What is the expected ratio of brown-eyed to red-eyed flies if the F1 progeny are grown at 29ºC? (ii) What is the expected ratio of brown-eyed to red-eyed flies if the F1 progeny are grown at 22ºC? (iii) What is the probability that a red-eyed F1 fly grown at 22ºC is homozygous?


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500 offspring were collected, all of which were grown at 22ºC. Among these flies, 105 had brown eyes and 395 had red eyes. You perform a χ2 analysis to test if the observed number of brown and red-eyed flies is consistent with Mendel’s principle of genetic segregation. (iv) The null hypothesis provides a precise experimental prediction that can be tested. In this problem, χ2 operates by comparing the observed frequencies (for example: 395 flies had red eyes and 105 flies had brown eyes) to the frequencies you expect from the Punnett square (for example, a 3:1 ratio). You want to know if your experimental results match the ratio the Punnett square predicts. State your null hypothesis. (v) How many red eye flies do you expect? (vi) How many brown eye flies do you expect? (vii) What is the χ2 value? (viii) How many degrees of freedom? (ix) What is the P-value (what two numbers is P between on the table)? (x) Write a short (2-3 sentences) interpretation of the P-value.


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8. Your neighbor tells you that her long hair, orange and black (with no white spots) cat named Remy was impregnated by a neighborhood cat. Remy just had kittens and she wants to know if you would like one. Remy – orange and black long hair cat with no white spots

You decide to adopt a black and white short hair female kitten named Bootsie:

You want to figure out who Bootsie’s father might be so you learn a little bit about cat coat color genetics:

1. A? cats are solid white (the dominant white phenotype masks the phenotypes associated with the B/b and XE/Xe genes). aa cats can be other colors (orange, black, brown etc.)

2. L? cats have short hair ll cats have long hair

3. BB have white patches on more than half of their bodies

Bb less than 50% of the cat’s fur is white bb no white spots on cat

4. XEXE female orange XEXe female mixed orange and black XeXe female black XEY male orange XeY male black


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Write the genotype of Remy (mom) and Bootsie (female kitten) and what you would predict for Dad’s genotype and phenotype.

Genes Remy’s (mom) Genotype

Bootsie’s (female kitten) Genotype

Predicted Dad Genotype

Predicted Dad Phenotype

Pigment (A or a) Hair length (L or l) Spotting (B or b) Color (XE or Xe)

Which of these neighborhood male cats could be Bootsie’s father? Describe why each cat could or could be Bootsie’s father.

Sam - all black long hair cat Snowy – all white short hair cat

Tiger – orange and white short hair cat Buttons – black and white long hair cat


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Loverboy – black and white short hair cat Turtle – orange and white short hair cat with white spots

Courses.washington.edu_gs361win_problems_PS3-2 %28Genome 361 Winter 2012%29

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