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Autosomal disorders

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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There are 44 autosomes in Man comprising 22 homologous pairs of chromosomes. Upon each chromosome, the genes have a strict order, each gene occupying a distinct locus in unison with its counterpart of maternal or paternal origin.

Alleles are alternative forms of genes which arise by mutation, normal types being referred to as 'wild'. If both members of a gene pair are identical then the individual is described as being homozygous, whereas if they are different, they are said to be heterozygous.

Gene-specified characteristics are termed traits. There are three types of disorder depending on the expression of traits:

  • autosomal dominant: trait is seen in the heterozygote
  • autosomal recessive: trait is seen only in homozygote
  • autosomal codominant: effect of both alleles seen in heterozygote

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