Pedigree analysis problem with solution (Example 11)

Pedigree analysis problem with solution (Example 11)

Q) For the following pedigree, give the most likely mode of inheritance, assuming that the trait is rare. Carefully explain your reasoning.

Solution:

Clue 1: Only males are affected

Assumption: The trait can be X-linked recessive or sex-limited autosomal dominant or Y linked.

Check possibility for these three modes of inheritance

Clue 2: Affected offspring does not have affected parents

  • This clue excludes the possibility for a dominant trait.
  • Unaffected parents do not transmit the disease in case of an autosomal dominant trait.
  • But it can be a sex limited autosomal dominant trait. Even though females carry disease allele, they remain unaffected (so skipping of generations will be possible). They can pass the trait to male child in the next generation and the disease will reappear in the pedigree.

1) Y linked trait

We can eliminate Y-linkage because affected males do not pass on the trait to their sons.

2) X linked recessive inheritance

  • Affected sons are born to unaffected mothers.
  • A carrier (heterozygous) mother produces approximately 1/2 affected sons.
  • Is never passed from father to son.

These three observations suggests that it follows X linked recessive inheritance pattern

 Sex limited (for males only) autosomal dominance can also be the mode of inheritance for this pedigree. You can check it by putting the genotype for each individuals.

 

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