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In autosomal (i.e. not X/Y sex chromosome determined) recessive disorders, possession of two copies of a
recessive allele can lead to development of the relevant disorder. This is due to the absence of a ‘dominant’ healthy gene. Examples are Tay-Sachs, sickle-cell anaemia and cystic fibrosis. Those who are heterozygous for a gene involved in an autosomal recessive disorder, one allele being the defective recessive variant, may exhibit a completely normal phenotype.
1 Carriers of a single recessive allele of a gene associated with an autosomal recessive disorder may feel some concern with respect to having children. Should they meet and marry a similar individual, what is the prospect of having healthy offspring, and what can they do about it? The actual odds of having healthy offspring were fairly well covered by Mendel.1 A carrier who knows his/her genetic inheritance may wish a partner to undertake genetic testing, just in case. If the position is known in advance then decisions may be affected by the seriousness or otherwise of the disorder in question.
