An albino girl gets married to a normal boy, What are the chances of their having an affected child and what are the chances of their children being carriers?
**Core Concept**
The question is testing the understanding of autosomal recessive inheritance patterns, specifically the genotype and phenotype of individuals with albinism. Albinism is caused by mutations in genes that code for enzymes involved in melanin production, such as tyrosinase. The condition is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to express the condition.
**Why the Correct Answer is Right**
In this scenario, the albino girl is homozygous recessive (bb) for the mutated gene, while the normal boy is homozygous dominant (BB) or heterozygous (Bb) for the gene. Since the boy is normal, he must be either BB or Bb. If he is BB, he cannot contribute a recessive allele to their offspring. If he is Bb, there is a 50% chance that he will pass the recessive allele to each child. The girl can only contribute a recessive allele (b) to her offspring. Therefore, the probability of their children being affected (bb) is 50%, and the probability of their children being carriers (Bb) is 50%.
**Why Each Wrong Option is Incorrect**
**Option A:** The question does not provide enough information to determine the genotype of the normal boy, but we know that the girl is homozygous recessive. Therefore, the probability of their children being affected cannot be determined without knowing the boy's genotype.
**Option B:** This option is incorrect because it does not accurately reflect the probability of their children being affected or carriers.
**Option C:** This option is incorrect because it does not accurately reflect the probability of their children being affected or carriers.
**Clinical Pearl / High-Yield Fact**
In autosomal recessive inheritance patterns, carriers (heterozygotes) are generally asymptomatic but can pass the mutated gene to their offspring. Individuals with albinism have a higher risk of skin cancer and vision problems due to the lack of melanin, which provides protection against UV radiation.
**Correct Answer:** D.