Interpreting Pedigree Diagrams

• Evidence for being sex linked:

  • only males are affected
• Evidence for an allele being autosomal dominant:

  • two affected parents have a child who is not affected, so both parents are heterozygous
  • if it was recessive then all the children of the affected parents would be affected
• Evidence for being autosomal recessive:

  • two non-affected parents have an affected child
  • both parents must be heterozygous carriers of the recessive allele.
• Evidence for being X-linked dominant:

  • all daughters from affected fathers are affected
  • this is because daughters receive one X chromosome from their father, who only has one.
• Evidence for being X-linked recessive:

  • All sons from affected mothers are affected. Unaffected mothers can still produce affected sons if heterozygous.
  • this is because sons receive their X chromosome from their mother