Question

1. For each of the following blood types, list the possible genotypes:

Phenotype           Possible Genotypes
A
B
AB
O

2. Dr. Paul is blood type O. His father was blood type A and his mother was blood type B.

1. What were the genotypes of his parents?
2. What are the possible blood types and phenotypic ratios expected for a cross involving these parental genotypes?

3. In the ABO blood system in human beings, alleles A and B are codominant and both are dominant to the O allele.  In a paternity dispute, type AB women claimed that one of four men was the father of her type A child.  What blood types could the father of the child be on the basis of the evidence given?

4. Hemophilia A in humans is caused by an X-linked recessive gene.

1. If a hemophiliac male mates with a homozygous non-hemophiliac female, what expected proportions and sexes among their offspring will be hemophiliacs?
2. If a daughter produced by the mating above mates with a normal male, what expected proportions and sexes among their offspring will be hemophiliacs?

5.Hemophilia in humans is inherited as an X linked recessive trait. A woman whose father is hemophiliac marries a man with normal clotting ability. What is the probability that her first child will have hemophilia? Assume that the woman's mother is homozygous dominant.

6. Pretend that a couple wants to have a child. The father is heterozygous for type A blood. The mother is heterozygous for type B blood and happens to be a carrier of hemophilia.

1. What is the probability that their first child will be type AB and have hemophilia?
2. The parents conceive, and amniocentesis reveals that the child is male. Recalculate your probability in A given this new information.

7. Duchenne muscular dystrophy (DMD) is caused by a relatively rare X-linked recessive allele. It causes progressive muscular wasting, and usually leads to death before age 20. What is the probability that the first son of a woman (who does not have the disease but whose father is affected) will be affected?

Answer 1

1.

Phenotype	Genotype
A	IaIa, IaIo
B	IbIb, IbIo
AB	IaIb
O	IoIo

2.

Mother = IaIo

Father = IbIo

Both the parents will be heterozygotes and will have one Io allele because Paul is IoIo.

Gametes	Io	Ib
Io	IoIo O	IbIo B
Ia	IaIo A	IaIb AB

PR - 1 : 1 : 1 : 1

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