Most traits, both physical and behavioral, are passed from parent to offspring, although some changes can arise due to a mutation or mistake in the genetic code. Genes found within the cells of all organisms carry the information necessary for all traits to be expressed. During sexual reproduction, offspring inherit one gene for each characteristic from one parent and another copy from the other parent. Autosomal dominant genes are one way that genes are inherited. The term autosomal dominant genesis often used to describe the method of inheritance of certain diseases and disorders.
Genes are the basis for all characteristics of an organism and exist in more than one form, called alleles. The different alleles for each gene code for different types of the same characteristic. For example, eye color is determined by the same gene, but differences in color are due to different alleles of this gene.
Not all alleles of a gene are expressed equally. Often, when a cell has different alleles for the same gene, one allele takes precedence over the other. The characteristic that is expressed is dominant to the one that is not. Continuing with the simplified eye color example, brown eye color is dominant to blue eye color. If a person has one allele for brown eyes and one allele for blue eyes, the person will have brown eyes.
All genes exist on long strands of DNA called chromosomes. Organisms that reproduce sexually have two types of chromosomes, autosomes and sex chromosomes. Sex chromosomes are the two chromosomes that determine the sex of the organism, while the autosomes are all the other chromosomes. Autosomal dominant genes is inheritance of characteristics found on the autosomes, not the sex chromosomes.
Diseases and disorders can be caused by a mutation, or a mistake, in a gene that is passed through families. Autosomal dominant inheritance of a disease or disorder means that the abnormal gene is located on one of the autosomes and the allele is dominant to the nonmutated form. In these cases, only one copy of the abnormal gene is required for the disease or disorder to be expressed in the offspring.
If a parent has a mutation in a dominant allele of a gene, there is a 50% chance that an offspring will also have the abnormal gene. As the mutation is located on one of the autosomes, the sex of the offspring will not affect the outcome of the disease or disorder. A common example of a disorder caused by autosomal dominant genes is Huntington’s chorea, or Huntington’s Disease.