In this section, you examined the inheritance of several
specific human traits. First, you studied how ABO and Rh blood groups are
inherited. ABO blood groups, which are of particular importance in blood
transfusions, are determined by multiple alleles. Two alleles, IA and IB, are codominant. One allele, i,
is recessive. Rh blood groups are determined by a dominant Rh positive allele
and a recessive Rh negative allele. Next, you learned about Huntington disease,
which is caused by a dominant allele. You then learned about sickle
cell anemia, which is caused by codominant alleles: one
for normal hemoglobin and one for sickle cell hemoglobin. Sickle cell
hemoglobin crystallizes when oxygen is in short supply, causing red blood cells
to become sickleshaped and rigid. The sickle-shaped blood cells tend to become
stuck in capillaries, blocking the flow of blood and thus damaging cells and
tissues. Finally, you read about polygenic traits in humans. Polygenic traits
include height and skin color.
ABO Blood Groups: Using the Main Ideas
Use the space provided to the side of the following
genetics problems to draw Punnett squares to help you solve the problems.
1. A man
with type 0 blood and a woman with type AB blood get married.
a. What
is the probability that they will have a child with type A blood? ___________
b.
Suppose that one of the couple's children needs an operation. This child has
type B blood. Can the child safely receive a blood transfusion from either
parent? Explain.
2. Vincent has type A blood and his mother has type 0 blood. Christine has type B blood and her father has type 0 blood.
a.
What is Vincent's genotype? ______ b. What is Christine's genotype?
_______
c. What genotype(s) might
Christine's mother have? ____________
d. Suppose Vincent and Christine get married. What is the probable phenotypic ratio for their offspring?________
e. What is the probable
genotypic ratio for their offspring? _______
3. The
allele for normal hemoglobin can be represented as HA. The allele for the sickle cell hemoglobin can be
represented as HS.
a. What type of gene interaction is involved in sickle
cell anemia?
Consider the offspring of two
people who both have the genotype HAHS.
b. What
percentage of their offspring are likely to be sickle cell sufferers? ______
c. What percentage of their offspring are likely to be
resistant to malaria and suffer few effects of the disease?__________
4. a. How is Huntington disease inherited?
b. What
is the probability that an individual who has one parent with Huntington will
also have the disease? (Assume the other parent does not have the disease)
5.
Phenylketonuria (PKU) is a genetic disease in which the body cannot safely
break down the amino acid phenylalanine. If untreated, PKU causes severe brain
damage. To avoid this, people with PKU must eat a special diet low in
phenylalanine.
Two
people who have normal phenotypes have a child. A blood test at birth shows
that the child has PKU
b. What is the probability that
this couple's next child will have PKU?
6. Achondroplasia, a form of dwarfism, is caused by the
dominant allele A. Embryos with the genotype AA do not survive. Suppose that
two people with achondroplasia get married and have children.
b. One of this couple's children, who has a normal
phenotype, marries a person who also has a normal phenotype. What percentage of
the children from this marriage are likely to have
achondroplasia? Explain.
7. The disease cystic fibrosis is caused by the recessive
allele n.
a. What percentage of the children of a couple with
genotypes NN and Nn will probably have cystic fibrosis? Explain.
b. What are the phenotypic and
genotypic ratios for the offspring of two people who both have the genotype Nn?