Red-green color blindness is carried on the X chromosome ($X^C$ normal vision, $X^c$ color blind). A woman of genotype $X^C{X}^c$ has children with a man of genotype $X^C$ Y. Use the square. What fraction of their sons is expected to be color blind?

A woman has normal blood clotting, but her father had hemophilia ($X^H$ normal clotting, $X^h$ hemophilia). Her mother carried no hemophilia allele. The square shows the cross that produced her, with the daughters' cells left blank. What is her genotype?

A boy has hemophilia ($X^H$ normal clotting, $X^h$ hemophilia). Neither of his parents has the condition. The square shows his parents' cross. From which parent did he inherit the hemophilia allele, and how?

In every population studied, far more males than females are red-green color blind. Which statement accounts for this difference?

A man who is red-green color blind ($X^c$ Y) has children with a woman of genotype $X^C{X}^C$. Use the square. Which statement describes their children?

A man is red-green color blind. Red-green color blindness is a recessive allele on the X chromosome ($X^C$ normal vision, $X^c$ color blind). What is his genotype?

A condition appears in nine males and no females across three generations of one family. Every affected male has an unaffected mother, and no affected man has an affected son. What does this pattern show?

A woman of genotype $X^H{X}^h$ has children with a man who has hemophilia, $X^h$ Y ($X^H$ normal clotting, $X^h$ hemophilia). Use the square. What fraction of their daughters is expected to have hemophilia?

A girl is red-green color blind ($X^C$ normal vision, $X^c$ color blind). What must be true of her parents?

The square shows the cross of a woman of genotype $X^H{X}^h$ with a man of genotype $X^H$ Y ($X^H$ normal clotting, $X^h$ hemophilia). Which genotype belongs in the cell marked with a question mark?

Hemophilia A occurs in roughly 1 in 5,000 male births and is far rarer in females. Which statement explains why an affected female is so rare?

The square shows the cross of a woman of genotype $X^H{X}^h$ with a man of genotype $X^H$ Y ($X^H$ normal clotting, $X^h$ hemophilia). Every daughter has normal clotting. Which genotype must a daughter have if she can pass hemophilia to a son of her own?

A white-eyed female fruit fly crossed with a red-eyed male gives red-eyed daughters and white-eyed sons. The reciprocal cross, red-eyed female with white-eyed male, gives all red-eyed offspring. What does the difference show?

A woman who is red-green color blind ($X^c{X}^c$) has children with a man who has normal vision ($X^C$ Y). What is true of their sons?

The square shows the cross of a color-blind man ($X^c$ Y) with a woman of genotype $X^C{X}^c$ ($X^C$ normal vision, $X^c$ color blind). One daughter of this couple is color blind. Which statement traces her two alleles?

The square shows the cross of a man who has hemophilia ($X^h$ Y) with a woman of genotype $X^H{X}^H$ ($X^H$ normal clotting, $X^h$ hemophilia). What is true of their daughters?

About 8% of males but only about 0.5% of females are red-green color blind, and some unaffected females carry the allele. Why does a female who carries one allele for color blindness still see color normally?

In fruit flies, eye color is carried on the X chromosome, with $X^W$ red and $X^w$ white. A white-eyed female ($X^w{X}^w$) is crossed with a red-eyed male ($X^W$ Y). Use the square. Which eye colors appear in the offspring?

A boy is red-green color blind and his sister is not. Their mother has normal vision and their father is color blind ($X^C$ normal vision, $X^c$ color blind). Where did the boy's $X^c$ allele come from?

In another family, a trait appears in about as many females as males in every generation, and one affected father has two affected sons. On which kind of chromosome does the gene lie, and what shows it?