Genes contain the information that tells our bodies how to grow, develop and work. Genes are passed from parents to children. We all have two copies of each gene in the cells of our bodies, one copy from each parent. Many illnesses are caused by inheriting faults in both copies of particular genes. These are known as autosomal recessive disorders.
People who have a fault in only one copy of these particular genes do not have the disease since they have a regular copy that can provide all the necessary information to the cells. They are called a “carrier” of the faulty gene. When both parents are carriers of the same faulty gene, there is a 1 in 4 chance that their children may inherit the faulty copy from both parents and thus be affected by the genetic disorder. This is called autosomal recessive inheritance.
A baby receives one copy of each gene from each parent, thus being a “mixture” of genetic information from his/her parents, see figure 1 and 2.
- Figure 1: When two unaffected carriers of the gene mutation become parents, for each pregnancy:
- There is a 1 in 4 (25%) chance that the child will inherit the regular gene copy from both parents and will be completely free of the gene fault and will not be affected by the disorder or be a carrier of the faulty gene (figure A).
- There is a 2 in 4 (50%) chance that the child will inherit both a regular copy and a faulty copy of the gene. The child will be a carrier of the faulty gene, UNAFFECTED by the disorder, just like his/her parents (figures B and C).
- There is a 1 in 4 (25%) chance that the child will inherit the faulty gene from both parents. This child WILL BE AFFECTED by the disorder (figure D).
- Figure 2 shows that if only one parent is a carrier, there is no chance that they will have a baby affected with the disorder, however, there is a 50% chance that each of their children will be carriers of the faulty gene.