Download Huntington`s disease is an example of a genetic disorder caused by

Dominant, Recessive, and Sex-linked Practice Problems
1. Huntington's disease is an example of a genetic disorder caused by
a. a late-acting lethal dominant allele
b. a nonlethal dominant allele
c. a late-acting recessive allele
d. homozygous recessive alleles
e. multiple alleles
2. Several inherited disorders are much more common in close-knit religious communities, such as
the Amish, than in the general population. Polydactyly (more than 5 fingers/toes per hand/foot) is
one such disorder. Polydactyly is a dominant allele disorder. An Amish couple decides to have a
child. The husband is normal, but the wife is polydactyl (heterozygous).
a. What is the husband’s genotype?
b. What is the wife’s phenotype?
c. What is the probability that their child would have polydactyly?
3. Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an
inherited metabolic disorder.
a. What inheritance pattern is described above?
b. What term would be used to describe the parents?
c. If alkaptonuria is like most other human hereditary disorders, what is probability of their
next child being born with alkaptonuria?
4. Theoretically, if a carrier hemophiliac married a normal male, what percentage of their male
offspring would be expected to be carriers?
5. A man with red-green colorblindness marries a woman who is neither colorblind nor a carrier for
this trait. Which statement would best describe their probable offspring?
a. All of their children would be colorblind
b. Fifty percent of their sons would be colorblind
c. Fifty percent of their daughters would be colorblind
d. None of their children would be colorblind but all of their daughters would be carriers.
e. All of their sons would be colorblind.
6. Cystic fibrosis can be inherited even if neither parent has the disease. This is because the disease
a. requires certain environmental conditions to be expressed
b. occurs only in polyploid individuals
c. is caused by a recessive allele
d. is caused by a dominant allele
e. occurs only in individuals who are already weak from other causes
7. Phenylketonuria (PKU) is an autosomal recessive disorder. Using "P" and "p" to represent the
alleles, what is the genotype of an individual
a. with PKU?
b. that appears normal but could pass the trait on?
c. that is normal?
8. Duchenne muscular dystrophy is caused by a recessive allele located on the X chromosome.
a. In the space provided, draw a Punnett square that shoes how two unaffected people can
have a child who has Duchenne muscular dystrophy.
b. Is the child with muscular dystrophy male or female?
c. What is the probability that the couple’s next child will have muscular dystrophy?
d. What is the phenotypic ratio of this cross?