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What does autosmal recessive inheritance mean?

Autosomal recessive inheritance occurs when the altered allele is recessive, and therefore a person needs to inherit two copies of the altered allele for the disease to express itself. Autosomal means that the altered gene is located on one of the 22 pairs of non-sex chromosomes (autosomes) and the altered allele is inherited from both the mother and the father, who each carry a mutated copy of the gene.

This type of inheritance is not limited to a specific gender and can affect both males and females, and it usually does not occur in all generations within a family. Both parents of an affected individual are usually healthy. When two carriers have a child, there is a 25% chance of the child inheriting two copies of the altered allele and, thereby, developing the autosomal recessive disease, a 50% chance of inheriting a single copy of the altered allele (thus not expressing the disease, but being able to transmit it to their offspring), and a 25% chance of inheriting two copies of the normal allele, which means that they are neither affected nor carriers of the disease allele.

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