Download Genetics Problem Set: Monohybrid and Dihybrid Crosses

Genetics Problem Set: Monohybrid and Dihybrid Crosses
Answer the following problems completely. Write out your detailes solutions to all problems on a sheet of
pad paper (use extra sheets if necessary). Box all final answers whenever appropriate.
1. Anna Sweetstory has a problem. Her eyes are half-closed all the time. Her teachers think she sleeps
during class and her friends think she is always bored. Anna’s condition is called ptosis, which is
caused by a single dominant gene, P. The opposite normal condition, open eyes, is caused by the
recessive allele, p. Anna’s father had ptosis, and his parents were both found to be homozygous
dominant with respect to this gene. Anna’s mother has normal eyes. [3 pts]
a. What is Anna’s genotype?
b. What are the genotypes of both her parents?
c. If Anna marries a man with normal eyes, what is the probability of their having a child with ptosis?
2. Albinism in humans is inherited as a simple recessive trait. For the following families, what are the
genotypes of the parents and offspring? (Note: When two alternative genotypes are possible, list them
both.) [4 pts]
a. Two non-albino (normal) parents have five children, four normal and one albino.
b. A normal male and an albino female have six children, all normal.
3. Pigeons may exhibit either a checkered or plain pattern. In a series of controlled matings, the following
data were obtained: [3 pts]
F1 Progeny
P Cross
CHECKERED
PLAIN
A. checkered x checkered
36
0
B. checkered x plain
38
0
C. plain x plain
0
35
a. How are the checkered and plain patterns inherited? Explain your answer.
b. What is your prediction on the result of the F1 x F1 mating from cross B.
4. Given the following individuals of a particular genotype: [3.5 pts]
i. AaBb
ii. AaBBcc
iii. AaBbcc
iv. AaBbCcDdEe
a. How many different types of gametes can be formed by each?
b. What are the allelic combinations of the gametes produced by i–iii? List all.
5. In peas, an allele for tall plants T, is dominant over the allele for short plants, t. An allele for another
independent gene produces smooth peas, S, and is dominant over the allele for wrinkled peas, s.
What are the genotypic and phenotypic ratios of the offspring of the following crosses: [4 pts]
a. TtSs x TtSs
c. ttSs x Ttss
b. Ttss x ttss
d. Ttss x ttSS
6. In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to
vestigial wings. Work through the following crosses through the F2 generation and determine the
genotypic and phenotypic ratios for each generation. Assume the parents are all homozygous. [4 pts]
a. gray, vestigial x ebony, long
b. gray, long x gray, vestigial
7. In guinea pigs, rough coat is dominant over smooth; black coat is dominant over white. A rough black
guinea pig bred with a rough white one gives the following results: [3.5 pts]
rough black
28
smooth black 11
rough white
31
smooth white 10
a. What are the genotypes of the parents?
b. To confirm your answer to the previous question, show a diagram of this cross, indicating all the
genotypes and phenotypes involved.
Biology 3 / Philippine Science High School-Main Campus
Problem Set #1