Overview of Single Gene Defects

What are genes?

Genes are determine your traits, such as eye color and blood type. They are contained on our chromosomes, which normally number 46 or 23 pairs in each cell of our body.

There are an estimated 25,000 genes contained on these 46 chromosomes. Genes are made of DNA. DNA is an acronym for deoxyribonucleic acid. DNA is made up of base pairs that code for certain proteins.

So, a gene, or a section of our DNA, makes a protein. There is also DNA in-between genes, which does not code for anything, but serves as a spacer. Therefore, our DNA is not always used to make protein products. 

Genes are found in pairs, just as the chromosomes are. One member of each gene pair is inherited from the mother, while the matching gene is inherited from the father.

Genes are expressed different ways. Some genes are dominant over others. In other words, genes are not always working. It depends on the combination of the gene pair inherited from the parents.

Genes on the first 22 pairs of chromosomes are autosomal. Autosomal means both males and females are equally likely to have this gene.

The last pair of chromosomes determine gender. Males have one X and one Y chromosome, while females have two X chromosomes. As a result, women do not have any of the genes present on the Y, and men have only one copy of genes on the X.

The idea of inheritance was first described by an Austrian monk, Gregor Mendel. To determine patterns of inheritance, Mendel performed experiments on garden peas.

These basic patterns are sometimes called Mendelian or traditional inheritance. The basic patterns of inheritance include: autosomal dominant, autosomal recessive and X-linked inheritance.