Autosomal inheritance

• Dominant/Recessive inheritance

  • A form of inheritance where genes are not expressed equally
  • The phenotypes for the dominant gene will be expressed if 1 or 2 copies of the allele are inherited from the parents. The dominant allele is represented by a capital letter
  • The phenotype for the recessive gene will be masked by the dominant gene
  • The only way the phenotype will be expressed is if 2 copies of the recessive gene are inherited. The recessive allele is represented by a lower case letter.
• Example 1 - Huntington’s Disease

  • An autosomal dominant disorder where patients progressively lose control over their motor functions
  • Autosomal means the gene loci is in the first 22 chromosomes (chromosome 4)
  • Dominant means that if a single allele is inherited its phenotype will mask all other allele phenotypes
  • The Huntington’s disease allele is dominant so represented: H
  • The normal allele is recessive so represented: h
• Example 2 - Phenylketonuria (PKU)

  • A disorder where an amino acid called phenylalanine is not broken down properly by the body.
  • This builds up in the nervous system damaging and killing nerve cells - leading to intellectual disability, seizures and death
  • PKU is an autosomal recessive disorder as the allele is found on chromosome 12 and its phenotype is masked by the normal phenotype