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Problem 1
Match each of the following key terms (a–i) with its description
below:
Key:
(a) alleles
(b) autosomes
(c) dominant allele
(d) genotype
(e) heterozygote
(f) homozygote
(g) phenotype
(h) recessive allele
(i) sex chromosomes
____ (1) genetic makeup
____ (2) how genetic makeup is expressed
____ (3) chromosomes that dictate most body characteristics
____ (4) alternate forms of the same gene
____ (5) an individual bearing two alleles that are the same for a particular trait
____ (6) an allele that is expressed whether in single or double dose
____ (7) an individual bearing two alleles that differ for a particular trait
____ (8) an allele that must be present in double dose to be expressed
Problem 2
Match the following types of inheritance (key terms a–f) with
the descriptions below:
Key:
(a) dominant-recessive
(b) incomplete dominance
(c) multiple-allele
(d) polygene
(e) sex-linked
(f) extranuclear
____ (1) only sons show the trait
____ (2) homozygotes and heterozygotes have the same phenotype
____ (3) heterozygotes exhibit a phenotype intermediate between those of the homozygotes
____ (4) phenotypes of offspring may be more varied than
those of the parents
____ (5) inheritance of ABO blood types
____ (6) inheritance of stature
____ (7) reflects activity of mitochondrial DNA
Problem 3
Describe the important mechanisms that lead to genetic variations in gametes.
Problem 4
Suppose that the ability to taste PTC (phenylthiocarbamide) depends on the presence of a dominant gene T; nontasters are homozygous for the recessive gene t. This would be a case of classical dominant-recessive inheritance.
(a) Consider a mating between heterozygous parents producing three offspring. What proportion of the offspring are likely to be tasters? What is the chance that all three offspring will be tasters? Nontasters? What is the chance that two will be tasters and one will be a nontaster?
(b) Consider a mating between Tt and tt parents. What is the anticipated percentage of tasters? Nontasters? What proportion can be expected to be homozygous recessive? Heterozygous? Homozygous dominant?
Problem 5
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?
Problem 6
A woman with blood type A has two children. One has type O blood and the other has type B blood. What is the genotype of the mother? What are the genotype and phenotype of the father? What is the genotype of each child?
Problem 7
In skin color inheritance, what will be the relative range of pigmentation in offspring arising from the following parental matches?
(a) AABBCC × aabbcc
(b) AABBCC × AaBbCc
(c) Aabbcc × aabbcc
Problem 8
Compare and contrast amniocentesis and chorionic villus sampling as to the time at which they can be performed and the techniques used to obtain information on the fetus’s genetic status.
Problem 9
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.
Problem 10
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.)
Problem 11
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.