Genes are what determine 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 30,000 to 35,000 different genes contained on these chromosomes. Genes are made of DNA. DNA stands for deoxyribonucleic acid. DNA is made up of base pairs that provide the codes for making proteins. So, ultimately, a gene, or a section of our DNA, makes a protein. There is also DNA located in between genes, which does not code for anything in particular, but simply serves as "spacer." Therefore, not all of the DNA in our cells is used to make protein products.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 it was inherited from. Genes that are present on the first 22 pairs of chromosomes are said to be autosomal. This means that both males and females are equally likely to have these genes. The last pair of chromosomes determines gender. Males have one X and one Y chromosome, while females have two X chromosomes. Therefore, 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 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. There are many different single gene defects that require clinical care by a physician or other healthcare professional. Listed in the directory below are some, for which we have provided a brief overview.