"Queen Victoria of England was a carrier of the gene for hemophilia. She passed the harmful allele for this X-linked trait on to one of her four sons and at least two of her five daughters. Her son Leopold had the disease and died at age 30, while her daughters were only carriers. As a result of marrying into other European royal families, the princesses Alice and Beatrice spread hemophilia to Russia, Germany, and Spain. By the early 20th century, ten of Victoria's descendents had hemophilia. All of them were men, as expected.
By comparison to the X chromosome, the much smaller Y chromosome has only about 26 genes and gene families. Most of the Y chromosome genes are involved with essential cell house-keeping activities (16 genes) and sperm production (9 gene families). Only one of the Y chromosome genes, the SRY gene, is responsible for male anatomical traits. When any of the 9 genes involved in sperm production are missing or defective the result is usually very low sperm counts and subsequent infertility. One in six American couples are infertile. It is now thought that about 1/3 of these couples is unable to have children as a consequence of the male mate not having the necessary sperm producing genes on his Y chromosome.
Because the Y chromosome only experiences recombination with the X chromosome at the ends (as a result of crossing-over), the Y chromosome essentially is reproduced via cloning from one generation to the next. This prevents mutant Y chromosome genes from being eliminated from male genetic lines. Subsequently, most of the human Y chromosome now contains genetic junk rather than genes."