PCB 3063– Sec 799 – In rats, several independently assorting autosomal genes affect

13 Jun PCB 3063– Sec 799 – In rats, several independently assorting autosomal genes affect

Question

PCB 3063– Sec 799

Summer C 2015

HOMEWORK

This homework is worth 30 points of the 400 points available in the course.

Please use the textbook, the PPT lecture handouts, and your comprehension of the corresponding course material, to answer the following ninequestions.

Instructions: To submit the homework, you need to use the worksheet file that I provided.

Simply type in the information in the appropriate spaces and submit the file via the Turnitin link. For full credit, you have to show your work.

Question 1: (5 points)

In rats, several independently assorting autosomal genes affect coat color. Gene A controls the distribution of yellow pigment in hair, and gene Bcauses black pigmentation. The two genes interact as follows: A–B– (gray),A–bb (yellow),aaB– (black), and aabb (cream). These genotypes are only expressed in the presence of the dominant allele of a third gene, C; rats with genotype cc are albino.

a. Deduce the genotype of each albino mice, to the extent that is possible, in the following table. Explain your answers.

True-breeding parents

F1

F2 offspring

Gray x albino-1

All gray

3/4 gray : 1/4 albino

Gray x albino-2

All gray

9/16 gray : 3/16 yellow : 4/16 albino

b. Deduce the genotype and phenotype of each parent in the following table. Explain your answers.

Parents

Numbers of offspring

Cross 1

135 gray, 83 albino, 47 yellow, 44 black, 16 cream

Cross 2

103 albino, 74 black, 25 cream

c. A gray-colored rat is mated with one that is yellow.The offspring include an albino rat and a cream-colored rat. Diagram this cross. Be sure to include the Punnett square and the phenotypic ratio in the offspring.

Question 2: (3 points)

The space probe HEA1 returns to earth following a trip to the planet Tantoun. Analysis of samples from this planet reveals that proteins are composed of 16 different amino acids, while DNA contains only two bases: rosine (R) and ziadine (Z).

a. What is the minimum codon size in this genetic code? Explain your reasoning.

b. How many of the codons in thisminimumgenetic code will contain at least
two Zs?Explain your reasoning.

Question 3: (4 points)

In this unit we have examined various mechanisms of non-Mendelian inheritance.
Please write a short essay (300-400 words) in which you compare and contrast the following mechanisms. Be sure to include how each deviates from simple Mendelian inheritance.

– Maternal effect

– Maternal inheritance

– Genomic imprinting

– Trinucleotide repeat diseases

Question 4: (2 points)

Consider two mice that are heterozygous for insulin-like growth factor 2.

From the cross Igf2 Igf2mXIgf2 Igf2m….

a. … what genotypic ratio would be expected?

b. … what phenotypicratio would be expected?

Question 5: (5 points)

Shown below is the pedigree of a rare neurodegenerative disease in humans.

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a. Based on the pedigree, characterize each of the following modes of inheritance as likely, unlikely, or impossible: autosomal dominant, autosomal recessive, Y linked, X-linked dominant, and X-linked recessive. Justify your reasoning.

Further scrutiny of members of this family reveals the following: 1) The disease’s degree of expression varies among individuals, with some mildly affected, others moderately affected and still others severely affected; and 2) Individual III-14 was previously married. Her ex-husband is phenotypically normal, with no history of the disease in his family going back ten generations. He has custody of the couple’s two children, a girl and a boy, both of whom are affected with the disease. The partial pedigree is shown below (the “slash” represents separation or divorce)

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b. Do these findings eliminate any of the remaining “likely or unlikely” modes of inheritance listed in part (a)? Are any of these modes of inheritance still possible? If so, which one(s) and why?

c. Is mitochondrial inheritance a likely, unlikely or an impossible mode of inheritance for this disease? Does it provide an explanation for the disease’s variable expressivity?

d. How can mitochondrial inheritance explain individual III-14?

Question 6: (2 points)

In a human population, the frequencies of alleles A and a are 0.8 and 0.2, respectively. Assume gene A is autosomal and the population is under Hardy-Weinberg equilibrium. If five people are randomly selected, what is the probability that exactly 3 AA and 2 Aa individuals will be picked?

Question 7: (3 points)

As we discussed in “lecture”,Rh is the most complex of the blood group types, involving at least 45 different antigens. The most clinically important antigen, D or RhO, is encoded by the gene RhDwhich is found on chromosome 1. Individuals that are Rh-positive have either one or two RhD genes, whereas the Rh-negative phenotype is caused by the absence of the RhD gene. (The antithetical allele d does not exist, however the letter “d” is used to indicate the D-negative phenotype). For the purpose of this homework, we will simplify things. Assume that the Rh blood group has only two alleles: the Rh-positive allele (D) and the Rh-negative allele (d).

Erythroblastosis fetalis (EF)is a condition that causes the mother’s red blood cells to attack those of the baby as if they were any foreign invaders. It is referred to as hemolytic anemia of the newborn. It is caused by anti-Rh antibodies from the mother which pass through the placenta and attack fetal blood cells that happen to be Rh-positive. Babies that are at risk for this condition are those with Rh-positive blood, whose mothers are Rh-negative (dd).

Side note:Here’s a current headline that addresses this condition. It’s well worth a read!

http://www.cnn.com/2015/06/09/health/james-harrison-golden-arm-blood-rhesus/index.html

Consider a population under Hardy-Weinberg equilibrium, where the frequency of the Rh-negative allele, d, is 0.3. What is the frequency of crosses that could potentially produce children with erythroblastosis fetalis?

Question 8: (3 points)

ABO blood type is studied in a Lebanese population, and these allele frequencies are determined.

f(IA)

0.30

f(IB)

0.15

f(IO)

0.55

What are the frequencies of the various genotypes and various phenotypes in this population? Assume Hardy-Weinberg equilibrium.

Question 9: (3 points)

In humans, the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the bitter compound PTC (phenylthiocarbamide) is dominant to the inability to taste this compound. Both traits are under the control of autosomal genes that are unlinked.

A population from Ghana is examined, and the following allele frequencies are calculated.

Dimples

Frequency

Tasting

Frequency

D

0.62

T

0.76

d

0.38

t

0.24

a. Determine the frequency of genotypes for each gene.

b. What are the expected frequencies of the four possible phenotype combinations:

dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters?