Patterns Of Inheritance

Autosomal disorders are carried on the autosomes (chromosomes 1-22) They affect males and females equally

Autosomal recessive disorders skip generations, it does not appear in every generation Sufferers require two recessive alleles to be affected (homozygous recessive). Two unaffected heterozygous carrier parents can have an affected child

Autosomal dominant disorders appear in every generation Each sufferer of the trait has an affected parent

In incomplete dominance the dominant allele does nto fully express itself Instead there are 2 versions of the gene e.g. H (normal) and S (affected) resulting in 3 different genotypes and 3 phenotypes e.g. normal (HH), affected (SS) and train (HS). Two trait parents can have an affected child The fully expressed form of the disorder occurs relatively rarely whereas partially expressed trait forms occur much more frequently

Sex linked recessive disorders are carried on the X chromosome, more males are affected than females Affected males do not pass the condition to their sons, they can only pass the condition to their daughters. Only affected or carrier females pass the condition to their sons. Unaffected males cannot pass the condition to their daughters