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STATISTICAL CHANCES OF INHERITING A TRAIT:
For an autosomal recessive disorder: When both parents are carriers
of an autosomal recessive trait, there is a 25% chance of a child inheriting abnormal genes from both parents, and therefore
of developing the disease. There is a 50% chance of each child inheriting one abnormal gene (being a carrier).
In other
words, if it is assumed that 4 children are produced, and both parents are carriers (neither exhibits any disease), the STATISTICAL
expectation is for:
- 1 child with 2 normal chromosomes (normal)
- 2 children with 1 normal and 1 abnormal chromosome (carriers, without disease)
- 1 child with 2 abnormal chromosomes (has the disease)
This does not mean that children
WILL necessarily be affected. It does mean that EACH child has a one in four chance of inheriting the disorder and a 50:50
chance of being a carrier.
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