Question

the pedigree on the right shows the inheritance pattern for an x - linked recessive disorder. how many individuals are carriers of the disease but are not affected? 3 x ⇒ 4 complete what is the genotype of the male circled in pink? ∘ xᵃy ∘ xᴬy ∘ xᵃyᵃ done

Explanation:

First Sub - Question (Number of Carriers)

Step1: Identify Carrier Symbol

In X - linked recessive pedigrees, a half - shaded circle (female) represents a carrier (has one recessive allele, not affected).

Step2: Count Half - Shaded Circles

Looking at the pedigree: The first generation (top) has 0 carriers (the male is affected, female is normal). The second generation: 2 half - shaded circles. The third generation: 0 carriers (the male is affected, females are normal? Wait, no, wait the fourth generation? Wait, no, let's re - examine. Wait, the pedigree: first row (top) male affected (shaded square), female normal. Second row: two half - shaded circles (females) and two normal squares. Third row: one affected square, two normal circles, two normal squares. Fourth row: two half - shaded circles, one normal square. Wait, no, let's count again. Wait, the correct count: in X - linked recessive, carriers are heterozygous females (\(X^A X^a\)). The half - shaded circles are carriers. Let's count the half - shaded circles: in the second row (children of the top affected male and normal female): 2 half - shaded circles. Then in the fourth row (children of the affected male in third row and a carrier? Wait, no, the affected male in third row (shaded square) has children: two half - shaded circles (females) and a normal square. So total carriers: 2 (second row) + 2 (fourth row)? Wait, no, the initial mistake: the first question's correct answer is 4. Let's see: the top affected male (\(X^a Y\)) has daughters. Each daughter gets his \(X^a\) and mother's \(X^A\), so they are carriers (\(X^A X^a\)): that's 2. Then the affected male in the third row (\(X^a Y\)) has daughters with a carrier? Wait, no, his wife: looking at the third row, the affected male is married to a normal female? No, wait the third row: the affected square is between two normal circles. Wait, no, the pedigree structure: top: shaded square (affected male) and normal circle (female). Their children: two half - shaded circles (carrier females) and two normal squares (males). Then, one of the carrier females (half - shaded) marries a normal square (male), their children: a normal circle, an affected square, a normal circle. The other carrier female marries a normal square, their children: a normal square. Then the affected square (male) marries a normal circle? No, wait the fourth row: the affected square (male) has children: two half - shaded circles (carrier females) and a normal square. Wait, so the carriers are: the two in the second row, and the two in the fourth row. So 2 + 2 = 4.

For X - linked recessive disorders, affected males have the genotype \(X^aY\) (they have the recessive allele on the X - chromosome and a Y - chromosome, as males have one X and one Y). The circled male is affected, so his genotype is \(X^aY\).

Answer:

4

Second Sub - Question (Genotype of Circled Male)