Genes and Inheritance

The Mixing of Genes Between You and Your Partner Determine the Physical and Mental Characteristics of your Child

A baby attains half of its genes from its father and half from its mother. Each sperm and egg have 23 chromosomes, which combine to form the 46 chromosomes in the resulting child. Every egg is comprised of X chromosomes, since the general chromosomal makeup of a woman is XX, or two X chromosomes. Similarly, and conversely, each sperm can be one of two chromosomes. Sperm can be comprised of either an X chromosome or a Y chromosome, since the general chromosomal makeup of a man is XY. Gender is determined at the moment of conception, since an X chromosome egg is either penetrated by a X chromosome sperm or a Y chromosome sperm.

Chromosomes are rod-like structures that contain genes. Genes determine the structure and function of every cell in the body, and are thus responsible for every characteristic that you inherit from your parents. Within the genes that you inherit from your mother and your father, some are dominant and some are recessive. Genes that are dominant prevail and become apparent in such aspects as outward appearance. Say your mother has brown eyes and your father has blue eyes. Blue eyes are from a recessive gene and brown eyes are from a dominant gene. But you have blue eyes. So how can you have blue eyes if your mother has the dominant brown eye gene? Since everyone receives two genes for everything, one from the mother and one from the father, it is possible that a blue eyed person and a brown-eyed person can have a blue eyed child (it is even possible for two brown eyed parents). Brown eyes can be the result of a brown eye gene and a blue eye gene. Since the brown eye gene is dominant and the blue is recessive, the person will have brown eyes, yet still have the gene for blue. (While a blue eyed person has two recessive genes for blue.) So a blue eyed father and a brown-eyed mother can have a blue-eyed child because the mother has a recessive gene for blue eyes that in her appearance has been dominated by the brown eyed gene. Such variations account for the differences between people, and siblings.