Normal female, whose father was color blind married a normal man. What are the chances of color blindness in son –
**Core Concept**
The question tests the understanding of **X-linked recessive inheritance**, specifically regarding **color blindness**, which is a common X-linked recessive trait. Color blindness is caused by mutations in the **OPN1LW** and **OPN1MW** genes on the X chromosome.
**Why the Correct Answer is Right**
Since the woman's father was color blind, she must be an **obligate carrier** of the color blindness gene, as she inherited one X chromosome from her father. When she marries a normal man, there's a chance she can pass this X chromosome to her sons, who have only one X chromosome.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not account for the mother being a carrier.
**Option B:** This option is incorrect as it suggests a higher probability than actually exists given the genetic scenario.
**Option C:** This option is also incorrect as it misrepresents the genetic risk.
**Option D:** This is not the correct probability based on X-linked recessive inheritance patterns.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that all daughters of a color-blind man will be **carriers** of the trait, while sons cannot inherit the trait from their father but can from their mother if she is a carrier.
**Correct Answer:** B. 50%.