A woman with severe discoloration of her tooth enamel has four children with a man who has normal tooth enamel. Two of the children, a boy (B) and a girl (G), have discolored enamel. Each has a mate with normal tooth enamel and produces several children. G has six children—four boys and two girls. Two of her boys and one of her girls have discolored enamel. B has seven children—four girls and three boys. All four of his daughters have discolored enamel, but all his boys have normal enamel. Explain the inheritance of this condition.

You have isolated two petite mutants, pet1 and pet2, in Saccharomyces cerevisiae. When pet1 is mated with wild-type yeast, the haploid products following meiosis segregate 2:2 (wild type : petite). In contrast, when pet2 is mated with wild type, all haploid products following meiosis are wild type. To what class of petite mutations does each of these petite mutants belong? What types of progeny do you expect from a pet1 × pet2 mating?

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Brown x White

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Wild type x Scarlet

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Wild type x White

In a large metropolitan hospital, cells from newborn babies are collected and examined microscopically over a 5-year period. Among approximately 7500 newborn males, six have one Barr body in the nuclei of their somatic cells. All other newborn males have no Barr bodies. Among 7500 female infants, four have two Barr bodies in each nucleus, two have no Barr bodies, and the rest have one. What is the cause of the unusual number of Barr bodies in a small number of male and female infants?

In cats, tortoiseshell coat color appears in females. A tortoiseshell coat has patches of dark brown fur and patches of orange fur that each in total cover about half the body but have a unique pattern in each female. Male cats can be either dark brown or orange, but a male cat with tortoiseshell coat is rarely produced. Two sample crosses between males and females from pure-breeding lines produced the tortoiseshell females shown.

Cross I     P: dark brown male × orange female

           F₁: orange males and tortoiseshell females

Cross II    P: orange male × dark brown female

           F₁: dark brown males and tortoiseshell females

The genetics service of a large veterinary hospital gets referrals for three or four male tortoiseshell cats every year. These cats are invariably sterile and have underdeveloped testes. How are these tortoiseshell male cats produced? Why do you think they are sterile?

In cats, tortoiseshell coat color appears in females. A tortoiseshell coat has patches of dark brown fur and patches of orange fur that each in total cover about half the body but have a unique pattern in each female. Male cats can be either dark brown or orange, but a male cat with tortoiseshell coat is rarely produced. Two sample crosses between males and females from pure-breeding lines produced the tortoiseshell females shown.

Cross I     P: dark brown male × orange female

           F₁: orange males and tortoiseshell females

Cross II    P: orange male × dark brown female

           F₁: dark brown males and tortoiseshell females

Why are tortoiseshell cats female?

In cats, tortoiseshell coat color appears in females. A tortoiseshell coat has patches of dark brown fur and patches of orange fur that each in total cover about half the body but have a unique pattern in each female. Male cats can be either dark brown or orange, but a male cat with tortoiseshell coat is rarely produced. Two sample crosses between males and females from pure-breeding lines produced the tortoiseshell females shown.

Cross I     P: dark brown male × orange female

           F₁: orange males and tortoiseshell females

Cross II    P: orange male × dark brown female

          F₁: dark brown males and tortoiseshell females

Explain the inheritance of dark brown, orange, and tortoiseshell coat colors in cats.