Question

1. baldness is a recessive sex-linked trait. if a normal headed woman whose father is bald, has children with a normal headed man, whose father was bald, what will be the genotypes and phenotypes of their children?

Explanation:

Step1: Define allele notation

Let $X^B$ = normal hair (dominant), $X^b$ = baldness (recessive); males have $X/Y$ chromosomes.

Step2: Find woman's genotype

Woman is normal-headed, father is bald ($X^bY$). She inherits his $X^b$, so her genotype is $X^BX^b$.

Step3: Find man's genotype

Man is normal-headed, father is bald ($X^bY$). Males inherit Y from father, so his genotype is $X^BY$.

Step4: Set up Punnett square

$$\begin{array}{c|cc} & X^B & Y \\ \hline X^B & X^BX^B & X^BY \\ X^b & X^BX^b & X^bY \\ \end{array}$$

Step5: Assign phenotypes

• $X^BX^B$: normal-headed female
• $X^BX^b$: normal-headed female
• $X^BY$: normal-headed male
• $X^bY$: bald male

Answer:

Genotypes and Phenotypes of Offspring:

1. $X^BX^B$: Normal-headed female
2. $X^BX^b$: Normal-headed female
3. $X^BY$: Normal-headed male
4. $X^bY$: Bald male

Probability breakdown: 50% normal-headed females (25% $X^BX^B$, 25% $X^BX^b$), 25% normal-headed male, 25% bald male.