Sex Depends on One Single Chromosome

A person's sex is determined at the embryonic level and depends on a single chromosome. This chromosome is the sex chromosome and can be either the X chromosome or the Y chromosome.

All germ cells, in both men and women, contain 23 chromosomes. One of these chromosomes is the sex chromosome. In women, eggs always contain an X chromosome, while in men, sperm can contain both an X chromosome and a Y chromosome.

If the egg unites with a sperm containing an X chromosome, the zygote, or fertilized egg, will have two X chromosomes and develop into a female child. If the egg unites with a sperm containing a Y chromosome, the zygote will have one X chromosome and one Y chromosome and will develop into a male child. Therefore, the probability of having a boy or girl is 50%.

Together with the 23 chromosomes of the father and mother, the embryo receives from 50,000 to 100,000 genes, or hereditary factors. These genes are carriers of traits that distinguish a person and make him unique. Although a person has similarities with his parents, he can also have unique traits that are not inherited from his parents.

Some genes, such as those responsible for eye or hair color, are inherited through dominant and recessive inheritance. Other genes, such as those associated with certain diseases, may be inherited in a more complex manner.

Although sex is determined by only a single chromosome, hereditary factors passed on from parents can interact in complex ways to determine a wide range of traits in a child.

Thus, the sex of the child depends on the presence of a certain sex chromosome in the sperm that fertilizes the egg. But, in addition to this, hereditary factors transmitted from parents also play an important role in the formation of the child’s traits and properties.