Sex-linked Recessive Pattern

Sex-linked recessive traits typically occur only in males. Because the sex-linked trait is invariably X-linked, males transmit the trait only to their daughters, all of whom become carriers. Carrier (heterozygous) females can then transmit the trait to 50% of their male and female offspring. Affected males are hemizygous for the X-linked trait.

Examples of X-linked recessive traits are hemophilia A, hemophilia B, Duchenne muscular dystrophy, and glucose-6-phosphate dehydrogenase deficiency.

See Figure 1-5.

Enrichment Activity 2

Visit Hemophilia and try the problem. Also visit the link to the tutorial on hemophilia at this site.

Just for fun, examine the pedigree of Queen Victoria and answer these questions. Email answers to Pat.

1. Queen Victoria's daughter Alice mated with Louis IV and produced seven children. What percentage of their daughters were carriers?

2. What percentage of their sons had hemophilia?

3. How does this compare with what would be expected for female and male offspring of a carrier mating with a normal male?

Inheritance Patterns

Sex-linked Recessive Pattern