Download Genetics problem set 1

Study problems in genetics
Physiology, Fall 2007
1. In humans, thalassemia shows incomplete dominance; heterozygotes exhibit a mild form
of the disease (thalassemia minor) and homozygotes, a much more severe form of
disease (thalassemia major). The inheritance of the ABO blood group system exhibits
both complete dominance (alleles A and B are recessive to allele O) and codominance
(alleles A and B). Both members of a couple have thalassemia minor. The husband has
blood type A, and his mother was blood type O. The wife has blood type AB. What is
the probability that they will have a child with:
a. no anemia and blood type A
b. thalassemia minor and blood type B
c. thalassemia major and blood type AB
2. In snapdragon plants, the allele for red flower color has an effect that is incompletely
dominant over the effect of the white color allele. If a cross between two plants
produced 18 red, 32 pink, and 15 white plants, what are the phenotypes of the parents?
3. Polydactyly is a dominant trait caused by gene P, as opposed to the normal allele p,
Cystic fibrosis, c, is recessive, as opposed to the normal condition, C. A polydactylous
woman, otherwise normal in phenotype, marries a healthy normal man. Their four
children have the following phenotypes:
Child
Child
Child
Child
a.
b.
c.
d.
1
2
3
4
is normal in all respects
is polydactylous, otherwise normal
has cystic fibrosis, otherwise normal
has cystic fibrosis and is polydactylous
What
What
What
What
is
is
is
is
the
the
the
the
genotype of the mother?
genotype of child 3?
genotype of child 4?
chance that child 1 is heterozygous for cystic fibrosis?