A 28 year old women suffering form sickle cell anaemia marries a 31 year old with no abnormality. What are the respective probabilities to have (i) sickle cell disease and (ii) sickle cell trait in their offspring?
**Core Concept**
The question involves the genetic inheritance of sickle cell disease, a recessive disorder caused by a mutation in the hemoglobin gene. Understanding the principles of Mendelian genetics, specifically the inheritance of recessive and dominant traits, is essential to answering this question.
**Why the Correct Answer is Right**
Sickle cell disease is an autosomal recessive disorder, meaning that a person must inherit two copies of the mutated gene (one from each parent) to express the disease. The parents are one carrier (heterozygous) and one non-carrier (homozygous for the normal allele). The offspring can inherit the mutated gene from the carrier parent, resulting in sickle cell trait (heterozygous) or sickle cell disease (homozygous for the mutated allele). The probability of each outcome can be calculated using a Punnett square.
* The probability of inheriting two copies of the mutated gene (sickle cell disease) is 25% (1 in 4).
* The probability of inheriting one copy of the mutated gene (sickle cell trait) is 50% (1 in 2).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the probability of inheriting sickle cell disease (25%) or sickle cell trait (50%).
**Option B:** This option is incorrect because it swaps the probabilities of sickle cell disease and sickle cell trait.
**Option C:** This option is incorrect because it does not account for the fact that the non-carrier parent cannot pass on the mutated gene.
**Option D:** This option is incorrect because it does not accurately represent the probability of inheriting sickle cell disease or sickle cell trait.
**Clinical Pearl / High-Yield Fact**
When counseling patients about genetic disorders, it's essential to understand the principles of Mendelian genetics and the probability of inheriting a particular trait. This knowledge can help patients make informed decisions about their reproductive choices.
**Correct Answer: D. 25% (sickle cell disease), 50% (sickle cell trait)**