Single gene disorders are disorders caused by a mutation in one gene. They usually follow the Mendelian pattern of inheritance.

We study these traits/disorders using Pedigrees; diagrams that show the relationships among family members. It is like a family tree that tells us who has/has a certain trait/disorder and who doesn't.

Based on what chromosomes they are carried on and how they are inherited, they can be classified in six ways:

  1. Autosomal Dominant Disorders
  2. Autosomal Recessive Disorders
  3. X-linked Dominant Disorders
  4. X-linked Recessive Disorders
  5. Y-linked Disorders
  6. Mitochondrial Inheritance Disorders

Autosomal dominant disorders

These are disorders that the diseased allele is dominant and is present on one of the autosomes(chromosomes 1-22).

  • This means that both the homozygous dominants and heterozygotes are affected.
  • The patients are mostly heterozygous as homozygous individuals were erased due to natural selection.
  • They mainly affect the nervous and skeletal system.

Examples include:

  • Alzheimer's disease
  • Huntington disease
  • Achondroplasia
  • Familial hypercholesterolemia
  • Neurofibromatosis
In autosomal dominant inheritance, the trait is equally distributed among both sexes and it does not skip a generation. The

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