(a) Give all the possible genotypes of the numbers
4, 5, 6 in the pedigree chart.
Answers
The following pedigree chart represents a X - linked recessive trait .
The possible genotypes of the numbers can be :
Number 4 : X′X
Number 5 : X′Y
Number 6 : XY
Explanation : Since , it is a X- linked recessive trait , it will only express itself when it is on X allele . In homozygous male , only single X is present , so they are most likely to be affected . In homozygous females , presence of this trait on single X allele makes them the carrier of the trait.
• Number 4 can be called as a carrier having genotype X′X because in the third generation , one of the progeny is affected . Since , the male partner in second generation , i.e. number 3 is not an affected individual , we are confirmed that the female number 4 is the carrier of this trait.
• Number 5 can be called affected as it can be seen clearly that the block is darkened making it suffering individual . Since , it is a male , the genotype would be X′Y .
• Number 6 can be called as a healthy individual as a male can either be healthy or can be affected . It can never be the carrier of the trait . Since , number 5 is not an affected individual as the block is not darkened , we can confirm its genotype XY .
The pedigree symbols are given in the attachment .
