29. Heredity

If a genetic counselor was examining a pedigree chart and noticed an occurrence of a disease in every generation, the counselor would most likely assume that the disease was caused by:

Women with X-linked disorders always pass the genes for the disorder on to ______. While men with X-linked disorders always pass the genes for the disorder on to _______.

Most children with cystic fibrosis are born to normal parents. Children with cystic fibrosis are homozygous for the recessive gene (cc). What can you conclude about the genotypes of the normal parents?

The Browns are both carriers of the recessive allele that causes the metabolic disorder called phenylketonuria. What is the probability of each of the following occurring?

(a) All three children will have the disorder.

(b) None of their three children will have the disorder.

(c) One or more of their children will have the disorder.

(d) At least one of their children will be phenotypically normal.

A color-blind man marries a woman with normal vision. The woman’s father was also color-blind.

(a) What is the chance that their first child will be a color-blind son? A color-blind daughter?

(b) If they have four children, what is the chance that two will be color-blind sons? (Be careful on this one.)

A genetic counselor has been consulted by a couple that is concerned about a dominant form of syndactyly (fused fingers or toes) in the male partner, Paul. Paul has syndactyly, as do his three brothers. His mother, his maternal grandparents, and his paternal grandfather do not have syndactyly, but his father and paternal grandmother do. The counselor constructs a pedigree spanning three generations for Paul’s family. Draw this pedigree and show the phenotype and genotype for each person.