Autosomal Recessive Genetic Disorders - Genetic Alliance UK

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2 Generally, the chance that someone who carries a gene with a change (mutation) will choose a partner who happens to carry the same changed (mutated) gene is small (if the partner is not a close relative and does not have a family history of the same genetic problem). If both partners in a couple are carriers of the same changed gene, they are at risk of having a child with a genetic disorder. The chance that such a couple will have an affected child is one in four (1 in 4, or 25%) for each pregnancy. Parents can sometimes misunderstand the 1 in 4 risk. Parents who have one child affected by a recessive disorder may think that a 1 in 4 risk means that the next 3 children cannot be affected. This is not true. The risk (25% or 1 in 4) is the same for every pregnancy. There is also a 2 in 4 chance that a child will inherit a single copy of the gene with the change (mutation). Children who inherit just one copy of the gene with the change (mutation) will be healthy carriers like their parents. This information is summarised in Picture 1.
3 Picture 1. How recessive genes are passed on by carriers These shapes represent a pair of genes This shape represents a normal copy of the gene This shape represents a copy of the gene with a mutation (change) Both parents are carriers; they both have a change (mutation) in one copy of the gene. They both have one normal copy of the gene. There are four possible ways for the parents to pass on their genes Father Mother unaffected child unaffected child unaffected child affected child neither gene has the both genes change (mutation) have the change (mutation) These children are carriers, like their parents
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Autosomal Recessive Genetic Disorders - Genetic Alliance UK

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