If the characteristic followed in the pedigree is x-linked recessive allele, what is III-1\'s
genotype? a. Hemizygous for a dominant allele b. Hemizygous for a recessive allele c.
Definitely heterozygous d. dominant e. Either heterozygous or homozygous dominant
Solution
1st generation parents 1,2 though are normal but must be heterozygotes (Pp) since their children
are affected i.e. 2nd generation males 1,3.
Since 1st generation male 3 is affected (pp) and 4 is normal but regardless if 4 in 1st generation
is PP or Pp their children will be either 4 Pp i.e. heterozygote or 2 affected pp and 2
heterozygotes Pp. But the 2nd generation 4, 5 female are normal but heterozygotes Pp.
So the cross between a 2nd generation affected male 3(pp) and a normal but heterozygote female
4(Pp) would have a normal male child only if hemizygous for a dominant allele condition exists.
Hemizygous is a condition in which only one gene copy/DNA sequence exists in diploid cells.
Males are hemizygous for most genes on sex chromosomes since they have only one X and one
Y chromosome unlike two X for females. A recessive X-linked gene requires two mutant alleles
to affect the female phenotype.
Rules followed here are.
If the characteristic followed in the pedigree is x-linked recessive .pdf
1. If the characteristic followed in the pedigree is x-linked recessive allele, what is III-1's
genotype? a. Hemizygous for a dominant allele b. Hemizygous for a recessive allele c.
Definitely heterozygous d. dominant e. Either heterozygous or homozygous dominant
Solution
1st generation parents 1,2 though are normal but must be heterozygotes (Pp) since their children
are affected i.e. 2nd generation males 1,3.
Since 1st generation male 3 is affected (pp) and 4 is normal but regardless if 4 in 1st generation
is PP or Pp their children will be either 4 Pp i.e. heterozygote or 2 affected pp and 2
heterozygotes Pp. But the 2nd generation 4, 5 female are normal but heterozygotes Pp.
So the cross between a 2nd generation affected male 3(pp) and a normal but heterozygote female
4(Pp) would have a normal male child only if hemizygous for a dominant allele condition exists.
Hemizygous is a condition in which only one gene copy/DNA sequence exists in diploid cells.
Males are hemizygous for most genes on sex chromosomes since they have only one X and one
Y chromosome unlike two X for females. A recessive X-linked gene requires two mutant alleles
to affect the female phenotype.
Rules followed here are
