Question

The pedigree below tracks Duchenne Muscular Dystrophy (DMD) through several generations. DMD is an X-linked recessive trait.

Pedigree of family with Duchenne Muscular Dystrophy
Pedigree of family with Duchenne Muscular Dystrophy
What is the genotype of individual II-2?
Choose 1 answer:
Choose 1 answer:
(Choice A)
\[\text{X}^{d}\text{Y}\]
A
\[\text{X}^{d}\text{Y}\]
(Choice B)
\[\text{X}^{D}\text{X}^{D}\]
B
\[\text{X}^{D}\text{X}^{D}\]
(Choice C)
\[\text{X}^{D}\text{X}^{d}\]
C
\[\text{X}^{D}\text{X}^{d}\]
(Choice D)
\[\text{X}^{d}\text{X}^{d}\]
D
\[\text{X}^{d}\text{X}^{d}\]

Answer 1

Individual II-2's genotype is X^dY, which reflects that he has Duchenne Muscular Dystrophy, an X-linked recessive disorder, as males with one affected X chromosome (X^d) will express this disease.

Step-by-step explanation:

The question deals with the genetic disorder Duchenne Muscular Dystrophy (DMD), which is a form of muscular dystrophy caused by an X-linked recessive gene. This means the defective gene responsible for the disorder is located on the X chromosome, and it is recessive, so a male (XY) will have the disease if his X chromosome carries the defective gene, since he does not have a second X chromosome to provide a normal copy of the gene.

Looking at the provided pedigree, individual II-2 is a male (identified by a square in the pedigree) who has inherited the disorder. Since DMD is an X-linked recessive disorder and knowing that males have one X and one Y chromosome, the affected male must have the affected gene on his single X chromosome.

Therefore, his genotype must be XdY, where Xd denotes the X chromosome with the Duchenne Muscular Dystrophy gene, and Y is the normal Y chromosome without the gene.

Thus, the genotype for individual II-2 would be Choice A: XdY.