What Is the Role of the Y Chromosome in Sex Determination in Humans?

By Mallory Malesky

Sex Chromosomes

Out of the 46 chromosomes humans have, only two are responsible for determining the sex of an individual. They are the X and the Y chromosomes. Females carry only the X chromosome, while males carry both X and Y. The X and Y chromosomes carry different genes, and the Y chromosome contains the genes that code for male attributes.

Sex Determination

All female eggs carry one X chromosome; therefore it is the chromosome carried in the sperm that determines the sex of the embryo at the moment of conception. If the egg is fertilized by a sperm with an X chromosome, the embryo develops into a female with an XX genotype. When the sperm carries a Y chromosome, a male embryo results, with an XY genotype.

Embryo Development

The genetic information within the Y chromosome contains the instructions to develop the embryo into a male; in particular, the chromosome has an area called the sex determining region Y (SRY). Until about week seven of a pregnancy, a male embryo and a female embryo are no different. Around this time, genes trigger the formation of the testes in a male embryo. The newly formed testes begin producing hormones, such as testosterone, that further contribute to the physical characteristics of a male.

Genetic Abnormalities

Abnormalities in the Y chromosome are generally not life-threatening or debilitating. A defect may result in incomplete male development and infertility. Additionally, it's possible for an embryo to receive two or more Y chromosomes. Although researchers are still studying this condition, males with extra Y chromosomes may be larger than average or have learning disabilities.