Observe the following:
(A) Huntington's disease
(B) Sickle cell anaemia
(C) Albinism
(D) Turner's syndrome
(E) Muscular dystrophy
Which of the above are not due to autosomal gene mutation ?

Question

Observe the following: 
(A) Huntington's disease 
(B) Sickle cell anaemia 
(C) Albinism 
(D) Turner's syndrome 
(E) Muscular dystrophy 
Which of the above are not due to autosomal gene mutation ?

Accepted Answer

The correct option is 4:

In the study of human genetics, it is crucial to distinguish between genetic disorders caused by a mutation in a single gene and those caused by an abnormality in the entire number or structure of chromosomes. The term "autosomal gene mutation" refers specifically to a defect in a gene located on any of the 22 pairs of non-sex chromosomes (autosomes). Option 4, which lists D and E, is the correct choice because both **Turner's syndrome (D)** and **Muscular dystrophy (E)** are **not** due to an autosomal gene mutation. Turner's syndrome is a classic example of a chromosomal disorder, or aneuploidy, where a female is born with only one X chromosome (45, X0). This condition is a result of non-disjunction of the sex chromosomes during gamete formation, not a mutation on an autosome. Similarly, the most common forms of Muscular Dystrophy, such as Duchenne Muscular Dystrophy (DMD), are X-linked recessive disorders. This means the defective gene (the DMD gene) is located on the X chromosome, which is a **sex chromosome**, not an autosome. Therefore, neither D nor E fits the definition of a disorder caused by an autosomal gene mutation.

The incorrect option is 1: A and B.

This option is incorrect because both Huntington's disease (A) and Sickle cell anaemia (B) are, in fact, caused by autosomal gene mutations. Huntington's disease is inherited in an autosomal dominant pattern, resulting from a mutation (CAG trinucleotide repeat expansion) in the *HTT* gene located on chromosome 4. Sickle cell anaemia is an autosomal recessive disorder caused by a single point mutation in the *HBB* gene on chromosome 11, leading to defective hemoglobin production. Since both A and B are categorized as autosomal gene mutations, they do not fit the criterion of the question (which asks for conditions *not* due to autosomal gene mutation).

The incorrect option is 2: A and C.

This option is incorrect because both Huntington's disease (A) and Albinism (C) are classic examples of autosomal gene mutations. As mentioned, Huntington's disease is an autosomal dominant disorder. Albinism, in its most common forms (Oculocutaneous albinism), is typically inherited in an autosomal recessive pattern, where the mutation affects genes like *TYR* on chromosome 11, which codes for the enzyme tyrosinase involved in melanin production. Since the gene mutation in both cases is on an autosome, they must be excluded from the correct answer.

The incorrect option is 3: B and E.

This option is partially incorrect. While Muscular dystrophy (E) is correctly identified as a non-autosomal disorder (it is X-linked), Sickle cell anaemia (B) is a condition that *is* caused by an autosomal gene mutation. Sickle cell anaemia is an autosomal recessive disorder, meaning the defective gene is on one of the 22 non-sex chromosomes. Because the question asks for the pair of conditions that are *not* due to an autosomal gene mutation, the inclusion of Sickle cell anaemia makes this option incorrect.