Download Genetics Problems

Honors Genetics Problems
Directions: Answer the following questions on your own paper. Be sure to show all of your work.
Monohybrid Crosses
1. Short hair is due to a dominant gene L in rabbits and long hair is due to a recessive allele l. A cross between a short
haired female and a long haired male produced a litter of 1 long haired and 7 short haired bunnies. (a)What are the
genotypes of the parents? (b) What phenotypic ratio was expected in the offspring generation? (c) How many of the
8 bunnies were expected to be long haired?
2.
In guinea pigs, black coat B is dominant over white coat b. If a homozygous black coated male was mated with a
homozygous white coated female, what would the genotype and phenotype of the F1 generation be? If two F1
offspring were mated, what would the genotypes and phenotypes of the F2 be?
3.
In a certain animal, black fur, B, is dominant to white fur, b. Determine the expected genotypic and phenotypic ratios
resulting from the following crosses: (a) homozygous black x white, (b) two heterozygous blacks, (c) heterozygous
black x white.
Dihybid Crosses
4. T= tall pea plants which are dominant to t=short pea plants. S=smooth seeds which are dominant to s=wrinkled seeds.
Cross a homozygous tall smooth plant with a short wrinkled plant. What are the genotypes and phenotypes of the F1
generation? Then cross two members of the F1 and give genotypes and phenotypes expected for the F2 generation.
5.
In cattle H=hornless allele dominant to h=horned and B=black allele is dominant to b=red. Give all the possible
genotypes and phenotypes expected in the following crosses: (a) horned red cow and a homozygous hornless,
homozygous black bull, (b) horned red cow and a heterozygous hornless, heterozygous black bull, (c) heterozygous
hornless, red cow and a horned, heterozygous black bull.
6.
In sheep, M=fine wool which is dominant to m=mealy wool. W=white wool which is dominant to w=red wool.
Cross a mealy red wooled sheep with a heterozygous fine, homozygous white wool sheep. Give the genotypes and
phenotypes expected from their offspring.
Incomplete Dominance
7. In snapdragons, yellow flowers (Y) are not dominant to red flowers (R) and vice versa. They will blend to make a
new color orange (RY). Complete the following crosses and give the genotypes and phenotypes of the offspring. (a)
Cross a red flower with a yellow flower, (b) cross an orange flower with an orange flower, (c) cross an orange flower
with a red flower.
Co-dominance
8. In cattle, roan cows are made from crossing a white haired cow and red haired bull. Red is not dominant over white
and vice versa. The colors exist at the same time. (a) Cross a roan cow with another roan cow. Give the genotypes
and phenotypes of their offspring.
Blood Type
9. A woman with type A blood marries a man with type O blood. The wife’s father is type O. What is the probability
that their expected child will be type O?
10. John has type O blood, his father is type B and his mother is type A. What are the genotypes of John’s parents?
11. If two newborn babies were accidentally mixed up in the hospital, there would be a question of which baby belonged
to which parents. From the following blood types, determine which baby belongs to which parents. Then determine
the genotype of each of the six people in the problem.
Baby 1
type O
Baby 2
type A
Mrs. Brown
type B
Mr. Brown
type AB
Mrs. Smith
type B
Mr. Smith
type B
12. One parent is homozygous for type A and the other parent has type O blood. What are all the possible blood types of
their children?
13. A child has type O blood. What are all the possible genotypes of his parents?
Sex Linkage-Remember the alleles are carried on the X chromosome. Nothing is carried on the Y.
14. The normal vision allele would be XC and the color blindness allele would be Xc. Sam has normal color vision. His
oldest sister is color blind and his younger sister has normal vision. What are the genotypes of his parents?
15. The disease where the blood does not clot is called hemophilia. It is a sex linked disorder. A man and his wife have 2
boys and 4 girls. One of the boys has hemophilia. The other boy and the girls do not. What are the genotypes of the
parents?
16. John is color blind. His brother Bill and his sister Sue are not. John’s father has normal vision. Is John’s mother
color blind? What are the genotypes of John’s parents and his sister?
17. A normal vision woman whose father was colorblind marries a normal vision man. They have two married daughters.
The first daughter has 5 sons, all with normal vision. The second daughter has two normal daughters and a colorblind
son. List the genotypes of all the above people.
18. Why is it not possible for a male to be heterozygous for colorblindness or hemophilia?
19. There are about ten times as many colorblind men as colorblind women. Explain why?
20. If a woman who is not a carrier of the genes for hemophilia is married to a man who is a hemophiliac, what
percentage of their male offspring could be expected to be hemophiliacs?
Pedigrees
Use the letter "f" to indicate the recessive Falconi anemia allele, and the letter "F" for the normal allele.
1. What is Arlene's genotype?
2. What is George's genotype?
3. What are Ann & Michael's genotypes?
4. Most likely, Sandra's genotype is
.
5. List three people from the chart (other than George) who are most likely carriers of Falconi anemia.