Question

20. View the above sex-linked recessive pedigree. Can you be certain of generation I, individual #1's

Answer 1

The genotype of the unknown individual is $X^BX^b$.

Males receive their X chromosomes from their mother.

They are not equally segregated among the male and female offsprings.

Explanation:

20. In case of the 1st pedigree problem, we can see that the male parent has the genotype of $X^bY$. And the female offspring has the genotype of $X^BX^b$. If the female gets the $X^b$ from her father, then $X^B$ has to be from the mother.

Now in the male offspring, the offspring gets the $X^b$ from mother, because males get the X chromosome from their mothers. So the mother has the genotype of $X^BX^b$.

21. The males have the genetic setup of 44 +XY. They get the 44 chromosomes equally from both the parents - 22 from father and 22 from mother. And as the mother has only X chromosomes as the allosomes, then the offspring gets Y chromosome from their father and X chromosome from their mother.

22. In the autosomal characters, the males have both pairs of functional chromosomes, so the relationship of dominant and recessive acts very well. But in case of the allosomes, they have only X chromosomes as the functional one, Y chromosome doesn't have any functional gene. So the gene which is present in X chromosomes, whether dominant or recessive, gets expressed in males. But in females, there are two X chromosomes, so the dominant and recessive characteristics gets reflected there. So in case of presence of one recessive allele, they becomes carriers.