Humans have 46 chromosomes in each cell in their body. These are arranged in 23 pairs. One chromosome in each pair is inherited from the mother and one from the father. 22 of the pairs are identical in males and females, and these are known as the ‘autosomes’. The 23rd pair consists of the two sex chromosomes, which determine the sex of the child.
Conditions described as ‘autosomal’ are those in which the defective gene (mutation) that causes the disorder is located on one of the 44 chromosomes other than the two sex chromosomes. Autosomal conditions affect both males and females equally.
If a condition is dominant, that means that a single copy of the affected gene is enough to cause the condition, even if the matching gene in the pair is normal. The abnormal gene ‘dominates’ the pair of genes. So a child inheriting the abnormal gene from an affected parent will also have the condition. If just one parent has a dominant gene defect, each child has a 50% chance of inheriting the disorder.
The image below shows the inheritance pattern for autosomal dominant disorders. Further information about genetics can be found in the links section to the left.