Recessive inheritance:
A genetic disorder is recessively inherited if an individual must possess two copies of the mutant allele in order to have the disease. When only one copy of the allele is present, the individual is referred to as a carrier, and does not usually exhibit any symptoms of the disease. Individuals who are homozygous with a recessive gene usually have both parents as carriers of the disease. This means that when they mate, each child has a 25% chance of inheriting the disease. There is a 25% chance that the child will not receive the mutant gene at all; a 50% chance that they will only receive one copy of this allele, and thus become a carrier themselves; and a 25% chance that they will receive the affected gene from both parents and thus, inherit the disease. It is usually identified in pedigrees by the way that it skips a generation, and then reappears in the F2 generation. Therefore, for the genes that are recessively inherited:
- Unaffected parents are able to produce offspring that do not inherit the disease.
- The affected offspring can be both male and female.
The incidence rate of recessive inheritance is quite rare, as it calls for two carriers to mate. The chances of this occurring is quite rare, and even when it does occur, the couple only have a 25% chance of producing an individual with the disease. However, it is more common amongst consanguineous marriages - marriages between close relatives. These types of marriages often occur because of cultural or geographical reasons and usually happen between first cousins. As they receive some of their genes from a common ancestor, the parents have a greater chance of being carriers for the same disorder. Examples of such disorders include haemophilia, cystic fibrosis and sickle cell anaemia.
- Unaffected parents are able to produce offspring that do not inherit the disease.
- The affected offspring can be both male and female.
The incidence rate of recessive inheritance is quite rare, as it calls for two carriers to mate. The chances of this occurring is quite rare, and even when it does occur, the couple only have a 25% chance of producing an individual with the disease. However, it is more common amongst consanguineous marriages - marriages between close relatives. These types of marriages often occur because of cultural or geographical reasons and usually happen between first cousins. As they receive some of their genes from a common ancestor, the parents have a greater chance of being carriers for the same disorder. Examples of such disorders include haemophilia, cystic fibrosis and sickle cell anaemia.