Question

12-13. Examine the pedigrees carefully and choose th Autosomal Dominant, Autosomal Recessive, or X-linked Recessive. Ex 12 e pattern of inheritance that the trait follows: plain your choice 13

Answer 1

12) A normal father and an affected daughter have both sons and daughters affected. Therefore this cannot be a X-linked trait because in order for girl child to be affected with a X-linked disease she must inherited one mutated X chromosome from each parent. Here the father is normal which means he has normal X-chromosome because males have XY genotype. If a male has a mutated X chromosome he is always affected as its genotype is hemizygous XY. Therefore this cannot be a X-linked trait and is an autosomal trait.

As can be seen in the pedigree the trait is expressed in every generation which is a feature of dominant trait. Thefore this pedigree represent an autosomal dominant trait.

13) This cannot be a X-linked trait as males are not heterzygous for X chromosome linked trait as they have only one X chromosome.

Here carrier parents are producing one affected homozygous child and other carrier children. When this affected child ( male) mates with an unaffected female, none of the progeny is affected but all are carrier. This is indicative of an autosomal recessive trait.

The genotype of generation 1 parents must be Aa as they heterozygous. Here a represent recessive mutant allele and A represent dominant allele.

Aa x Aa : AA, Aa, Aa, aa ( affected child)

The genotype of the female with who this affected child later on marrier must be AA as she is normal homozygous.

aa x AA : Aa ( all are carriers)

The similar pattern is seen in the pedigree. The cross of a homozygous normal female and homozygous recessive individual produce all carrier progeny.

The trait is also skipping generation which is a feature of an autosomal recessive trait.

Therefore the given pedigree represent an autosomal recessive trait.