What is the significance of x and y chromosomes

Forgot your password? Get help. Privacy Policy. Create an account. Password recovery. All Trends for Trends for Identifying the Next Frontier in Vaccine Manufacturing. Educating Next-Generation Bioprocess Engineers. In , German biologist Hermann Henking counted 11 chromosomes in firebug Pyrrhocoris apterus sperm nuclei. McClung soon hypothesized that the accessory chromosome determined male sex. In , Wilson, the more established scientist, described a pair of unequally sized chromosomes, which segregated in a ratio among insect sperm.

A month later, Stevens reported a similar discovery in beetle gonads. Extra genetic material from the X chromosome interferes with male sexual development, preventing the testes from functioning normally and reducing the levels of testosterone a hormone that directs male sexual development in adolescent and adult males.

Extra copies of genes from the pseudoautosomal region of the extra X and Y chromosomes contribute to the signs and symptoms of 48,XXYY syndrome; however, the specific genes have not been identified. Deletions of small amounts of genetic material in certain areas of the Y chromosome lead to a condition called Y chromosome infertility.

This condition affects the production of sperm and makes it difficult or impossible for affected men to father children. The deletions occur in areas of the Y chromosome called azoospermia factor AZF regions. Genes in these regions provide instructions for making proteins thought to be involved in sperm cell development, although the specific functions of these proteins are unknown. Deletions in the AZF regions remove all or part of several genes, or, in rare cases, a single gene.

Loss of this genetic material likely prevents the production of one or more proteins needed for normal sperm cell development. As a result, sperm develop abnormally or do not develop at all, leading to Y chromosome infertility. Chromosomal conditions involving the sex chromosomes often affect sex determination whether a person has the sexual characteristics of a male or a female , sexual development, and fertility. The signs and symptoms of these conditions vary widely and range from mild to severe.

They can be caused by missing or extra copies of the sex chromosomes or by structural changes in these chromosomes. Rarely, males may have more than one extra copy of the Y chromosome in every cell polysomy Y.

The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the features of these conditions are variable. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Figure 3: Example set of male human chromosomes. In the image, the X and Y chromosomes are indicated by arrows.

Figure 4: Sex determination in humans. On the upper left, the female parent genotype is XX. The first X is labeled to the left of the top quadrant, while the second X is labeled outside the left quadrant. On the upper right, the male parent genotype is XY. The X is labeled to the right of the top quadrant, while the Y is labeled outside the right quadrant. In this case, two of the four quadrants contain the genotype XX, resulting in female offspring; the remaining two quadrants contain the genotype XY, resulting in male offspring.

Figure 5: Sex determination in insects. On the upper right, the male parent genotype is X-. The X is labeled to the right of the top quadrant, while the minus sign is labeled outside the right quadrant. In this case, two of the four quadrants contain the genotype XX, resulting in female insects; the remaining two quadrants contain the genotype X-, resulting in male insects.

Figure 7: A side-by-side comparison of sex determination systems in humans, insects, and birds. The diagram looks like a diamond that has been divided into four equal square cells. The second Punnett square represents the sex determination system in insects.

In this case, two of the four quadrants contain the genotype XX, resulting in female offspring; the remaining two quadrants contain the genotype X-, resulting in male offspring. The third Punnett square represents the sex determination system in birds. In this case, two of the four quadrants contain the genotype ZZ, resulting in male offspring; the remaining two quadrants contain the genotype ZW, resulting in female offspring. More on sex determination. In some animals, sex can be determined by environmental conditions Sex Determination in Honeybees Scientists report sex reversal in a transgenic mous.

The variety of inheritance patterns described in this article illustrate that sex determination is a complex and varied feature among organisms. Key Questions How can environmental conditions determine sex in some animals?