genetics

• Allele - alternative forms of a gene.
• Genotypes - the description of alleles that an individual inherits.
• Autosomal recessive disorders are expressed very rarely and often skip generations, affecting both males and females equally.

  Example: Cystic fibrosis

  • Sufferers are homozygous recessive
• In autosomal dominant disorders, affected individuals will always have an affected parent, it affects both males and females equally. When the trait does not appear in a branch it won’t appear in future generations.

  Examples include: Huntington’s chorea

  • Sufferers are homozygous dominant or dominant heterozygous
• With incomplete dominance disorders, carriers of the allele show a mild form of the trait, as neither allele is completely dominant over the other.

  Example: Tay Sachs disease.
• Occurs on the X chromosome. Sex linked recessive disorders always have more males affected than females. None of the sons of affected males are affected, however grandsons of affected males can show the trait.

  Example: Colour blindness and haemophilia
• An autosomal disorder gene mutation is located on chromosomes 1 to 22 while a sexlinked gene mutation is located on the X chromosome.