Y Chromosome: Definition, Disorders & Structure

Instructor: John Williams
The Y chromosome is found in males and is one of two chromosomes that determine gender. This article focuses on the Y chromosome, the genes it contains, and disorders that are related to this structure in men.


Gender is determined by the combination of chromosomes that are found in the 23rd pair of the human genome. These are aptly known as the sex chromosomes (or allosomes), and contain genes that encode for sex-linked traits. The traits on the X chromosome are numerous, and have been mapped and discussed heavily in genetics. The Y chromosome, although it contains fewer genes, is responsible for the traits that are attributed to males in the human population. Let's discuss the traits and genes that reside in the Y chromosome.

The Y Chromosome: What Makes the Man?

The Y chromosome was discovered in 1905 to be a sex-determining chromosome. Originally, it was thought that the X chromosome was responsible for determining male/female development. However, with the discovery of the Y chromosome, scientists determined that the presence or absence of the Y chromosome was the key determinant, and that this factor is a better predictor of gender in developing individuals. Therefore, the Y chromosome became a very important discovery in the field of human genetics.

Karyotype of the Human Genome. The box indicates the XY genotype for males.

The Y chromosome, under normal circumstances, is found exclusively in the male. It is smaller than the X chromosome and is thought to be shrinking in successive generations in terms of the amount of genes and overall size. The genes on the Y chromosome encode several aspects of male individuals.

Genes on the Y Chromosome

The Y chromosome contains genes that are both simple to understand and more complex in terms of male development. For example, ear hair is normally formed from the expression of a gene on the Y chromosome. Women typically do not have ear hair, but some men do. This is a gene that is simple to understand.

More complex genes include the SRY gene, which is important for the development of the male gender specifically. This gene will override the common genes found in both males and females to promote the male phenotype (characteristics). Additionally, the Y chromosome contains the AZF gene, which is responsible for producing proteins for sperm development.

Defects in the Y Chromosome

There is only one disease that has been well-defined as it relates to the Y chromosome, and that is defective testicular development. Whenever a male has a mutation in the SRY gene, it can cause the testicle to under-develop. Additionally, mutations in the AZF gene can lead to Y-chromosome infertility. These two conditions are the most researched of all conditions on the Y chromosome.

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