One of the classic X-linked traits is hemophilia, a disease where blood fails to clot properly. In addition to the classical hemophilia A, some of the well known X-linked recessive genes include those producing various types of color blindness, glucose-6-phosphate dehydrogenase deficiency, Lesch-Nyhad syndrome, Duchenne muscular dystophy, and ichthyosis. A few X- linked dominant genes have also been identified. An X-linked dominant gene appears to be the cause of vitamin D-resistant rickets. The production of a certain blood antigen, the X antigen, is also due to a dominant X-linked gene (symbolized as X ^a _g ). Consider the following questions, and answer them on the lab report sheet.

1. Would you expect X-linked recessive alleles such as the ones form hemophilia and color blindness to be more frequently expressed in males or in females? Why?

2. Would you expect an X-linked dominant allele such as X, to be more commonly expressed in males or in females? Why?

3. If a woman having normal color vision marries a color-blind man and they have one child, a color-blind son, from whom did the son inherit color blindness; his mother, his father, or both

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