Percentage of offspring affected by colour blindness when a healthy male and heterozygous female marry
**Core Concept**
Inheritance of color blindness is primarily governed by the X-linked recessive gene, where the condition is more prevalent in males due to having only one X chromosome. This question tests the understanding of the genetic probability of inheriting color blindness when a healthy male and a heterozygous female marry.
**Why the Correct Answer is Right**
When a healthy male (who is not colorblind) and a heterozygous female (who has one normal and one colorblind X chromosome) marry, only the colorblind allele can be passed down to their offspring. Since the female is heterozygous, there is an equal chance of passing either the normal or colorblind allele to her offspring. As a result, half of her offspring will inherit the colorblind allele, making them colorblind. This is because the healthy male can only pass his Y chromosome to his male offspring, making them colorblind, while all his female offspring will inherit his X chromosome and the colorblind allele.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the genetic probability of inheriting the colorblind allele from the heterozygous female.
**Option B:** This option is incorrect because it does not accurately represent the chances of inheriting the colorblind allele from the heterozygous female.
**Option D:** This option is incorrect because it overestimates the chances of inheriting the colorblind allele from the heterozygous female.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that color blindness is an X-linked recessive trait, and females are rarely affected due to having two X chromosomes. However, when a female is heterozygous, there is a 50% chance of passing the colorblind allele to her offspring.
**Correct Answer:** C. 50%