Virginia Commonwealth University

VCU Massey Cancer Center

Genes

What are genes?

Genes are what influence your traits, such as eye color and blood type. They are contained on our chromosomes, which normally number 46 total (23 pairs) in each cell of our body. There are an estimated 20,000 to 40,000 different genes contained on these chromosomes. Genes are made of DNA, which stands for deoxyribonucleic acid. DNA is made up of base pairs that often provide the codes for making proteins. So, ultimately most genes, or sections of our DNA, make proteins.

Genes are found in pairs, just as the chromosomes are. One member of each gene pair is inherited from our mother, while the corresponding member of the gene pair is inherited from our father. Genes are expressed in different ways. For some genes, both copies are needed in order for the protein they make to work properly in the body. For other genes, only one copy is necessary. For yet other genes, how the gene works depends on which parent “supplied” it.

Genes that are present on the first 22 pairs of chromosomes are said to be autosomal — meaning that both males and females are equally likely to have these genes. The last pair of chromosomes determines sex. Males have one X and one Y chromosome, while females have two X chromosomes.

The idea of discrete units of inheritance was first described by an Austrian monk whose name was Gregor Mendel. Mendel performed experiments on garden peas to determine patterns of inheritance. These basic patterns are sometimes called “Mendelian” or “traditional” inheritance. The basic patterns of inheritance are: autosomal dominant, autosomal recessive and X-linked inheritance.