Biology 155: Worksheet- Mendelian Genetics Problems

Name: ___________________________________ Lab Section: ________

Answer the following questions. Show all your work for full credit. (15 pts. total.)

1. Based on what you have learned about Mendel’s experiments with pea plants, which two of the following statements is not correct? (0.5 pt.)

A. The gene for wrinkled seeds is an allele of the gene for smooth seeds.

B. White flowers and purple flowers are determined by different alleles of the same gene.

C. The gene for wrinkled seeds is an allele of the gene for purple seeds.

D. The alleles for smooth seeds and purple flowers are dominant.

2. In humans, dimples is inherited as a dominant trait. A man heterozygous for dimples marries a woman without dimples (1 pt.).
1. What are the genotypes of the couple?

Father: Mother:

2. What proportion of their children will have dimples?

3. In guinea pigs, the allele for black fur (B) is dominant over the allele for white fur (b). A back male guinea pig is mated to a white female guinea pig. The offspring were 7 black and 6 white guinea pigs. What are the genotypes of the parents? (1 pt.)

Father: Mother:

4. A diploid cell would have which of the following? (0.5 pt.)

A. Two sister chromatids for each chromosome.

B. Two homologs for each chromosome

C. Two genes for each allele

D. Two different alleles for each gene

5. A brown mouse is mated to a white mouse and all of their offspring are brown (1.5 pt.).
1. Give a name to the gene responsible for this trait, and assign symbols for the possible alleles. Which allele is dominant?

2. What are the genotypes of the mice that were crossed?

3. If two of the brown offspring were mated together, what percentage of the F₂ mice would be brown?
5. In tomatoes, red fruit (R) is dominant to yellow fruit (r). A true breeding red-fruited plant is bred to a true-breeding yellow-fruited plant (1 pt).

1. What phenotypic ratio would you expect to see in the F1 offspring?

2. If two of the F1 plants were bred, what phenotypic ratio would you expect to see in the F2 offspring?

3. What genotypic ratio would you expect to see in the F2 offspring?

7. In fruit flies, curly wings (c) is recessive to straight wings (C). Ebony body (e) is recessive to tan body (E). Suppose you had a male fly that had curly wings and was heterozygous for body color and a female fly that was heterozygous for wing type and had had an ebony body (1.5 pt.).
1. What is the genotype for the male fly?

2. What type of gametes could the male fly produce?

3. What is the genotype for the female fly?

4. What type of gametes could the female fly produce?

5. Construct a Punnett Square to determine the PHENOTYPIC ratio that you would expect to find in the offspring of these two flies.

8. A recently married couple are both heterozygous for cystic fibrosis, a recessive genetic disorder. They would like to start a family and would like to have two children (1.5 pt.).

1. What is the probability that their first pregnancy would result in a child with cystic fibrosis?

2. What is the probability that their second pregnancy would result in a child with cystic fibrosis?

3. What is the probability that both their first and second child would have cystic fibrosis?

9. Tim and Jan both have freckles, but their son Michael does not. Show with a Punnett square how this is possible. If Tim and Jan have another child, what is the probability that it will have freckles? (0.5 pt.)

10. Both Tim and Jan (from problem 9) have a widow’s peak, but Michael has a straight hairline (1 pt.).
1. What are Tim, Jan, and Michael’s genotype for hairline type?

2. If Tim and Jan had another child, what would be the probability of that child having both freckles and a widow’s peak?

11. In shorthorn cattle, the heterozygous condition of the alleles for red coat color (C^R) and white coat color (C^W) is a sandy color called roan. If two cattle with roan coats are mated, what phenotypic ratio of offspring will be produced? (1 pt.)

12. The following pedigree shows the transmission of a rare, but not fatal, genetic disorder in a family (1 pt.):

A. Identify the mode of inheritance suggested by the pedigree.

B. Indicate the genotypes of all the individuals in the pedigree above.

13. In the following pedigrees, state by answering yes or no in the appropriate blank space, whether transmission of the trait could be accounted for on the basis of each of the listed simple modes of inheritance (1.5 pt.):

	Pedigree A	Pedigree B
Autosomal recessive	__________	__________
Autosomal dominant	__________	__________
X-linked recessive	__________	__________

14. Both John and Cathy have normal colorvision. After 10 years of marriage, Cathy gives birth to a colorblind son. John filed for divorce, claiming he’s not the father of the child.

(i) Is John justified in his claim for nonpaternity? Explain why (0.5 pts.)

(ii) From which grandparent could the son have inherited his X chromosome? (1 pt.)

Cathy’s Mom: _________ Cathy’s Dad: _________

John’s Mom: __________ John’s Dad: __________