Karyotype analysis of human gametes provides evidence that each egg produced by a female carries one X chromosome. Half of the sperm cells produced by a male carry an X chromosome and half carry a Y. If an X-bearing sperm fertilizes an X-bearing egg, the new individual will develop into a female. Conversely, if the fertilizing sperm carries a Y chromosome, the individual will develop into a male.
Among the very few genes on the Y chromosome is a “male-determining gene.” Expression of this gene leads to the formation of testes, which are the primary male reproductive organs. In the absence of this gene, ovaries form automatically. Ovaries are the primary female reproductive organs. Testes and ovaries both produce hormones that govern the development of particular sexual traits.
A human X chromosome probably carries more than 300 genes. Like other chromosomes, it carries some genes associated with sexual traits, such as the distribution of body fat. But most of its genes deal with nonsexual traits, such as blood-clotting functions.
Among the very few genes on the Y chromosome is a “male-determining gene.” Expression of this gene leads to the formation of testes, which are the primary male reproductive organs. In the absence of this gene, ovaries form automatically. Ovaries are the primary female reproductive organs. Testes and ovaries both produce hormones that govern the development of particular sexual traits.
A human X chromosome probably carries more than 300 genes. Like other chromosomes, it carries some genes associated with sexual traits, such as the distribution of body fat. But most of its genes deal with nonsexual traits, such as blood-clotting functions.
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