**Core Concept**
Inheritance of an X-linked recessive trait involves a genetic disorder that is caused by mutations in genes located on the X chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). X-linked recessive traits are more common in males because they have only one X chromosome, making them more susceptible to expressing the trait if they inherit an affected X chromosome.

**Why the Correct Answer is Right**
When a female carrier of an X-linked recessive trait has a male child, there is a 50% chance that the male child will inherit the affected X chromosome and express the trait. This is because the male child only needs to inherit one X chromosome from the mother to be affected. In this case, the mother is a carrier, meaning she has one normal X chromosome and one affected X chromosome. When she passes on her X chromosomes to her offspring, there is a 50% chance that the male child will inherit the affected X chromosome.

**Why Each Wrong Option is Incorrect**
**Option B:** This statement is incorrect because a female who inherits an affected X chromosome from her father will be affected herself, not a carrier. Females are more likely to be carriers of X-linked recessive traits because they have two X chromosomes and can compensate for the affected X chromosome with their normal X chromosome.

**Option C:** This statement is incorrect because fathers cannot transmit X-linked recessive traits to their sons, as the Y chromosome is involved in male inheritance and does not carry the genes responsible for X-linked recessive traits.

**Option D:** This statement is incorrect because mothers can transmit X-linked recessive traits to their daughters, but it is less likely for the daughter to be affected because she has two X chromosomes and can compensate for the affected X chromosome with her normal X chromosome.

**Clinical Pearl / High-Yield Fact**
Remember that X-linked recessive traits are more common in males because they have only one X chromosome, making them more susceptible to expressing the trait if they inherit an affected X chromosome. This is why these traits often manifest in males, while females are more likely to be carriers.

**✓ Correct Answer: A. 50% of boys of carrier mother are affected**