Which of the following disorders are the results of aneuploidy?

(A) Haemophilia

(B) Down’s Syndrome

(C) Thalassemia

(D) Turner’s Syndrome

The correct option is (B) and (D) only.

Step-by-step Explanation:

1. Understanding Aneuploidy:
Aneuploidy is a genetic condition where there is an abnormal number of chromosomes in a cell. This occurs when an individual is missing a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). It is primarily caused by non-disjunction, which is the failure of sister chromatids or homologous chromosomes to separate properly during cell division (mitosis or meiosis).

2. Analyzing the Given Disorders:
Let us evaluate each of the disorders listed in the question:

* (A) Haemophilia: Haemophilia is a sex-linked recessive Mendelian disorder characterized by the lack of blood-clotting factors. It is caused by mutations in specific genes on the X chromosome, not by an abnormal chromosome count (aneuploidy).
* (B) Down's Syndrome: Down’s Syndrome is a classic example of aneuploidy. It is a chromosomal disorder caused by the presence of an additional copy of chromosome number 21, leading to trisomy 21. Therefore, individuals with Down's syndrome have 47 chromosomes instead of the normal 46.
* (C) Thalassemia: Thalassemia is an autosomal recessive Mendelian disorder. It is caused by mutations or deletions in the genes responsible for the synthesis of globin chains of hemoglobin, not by an alteration in chromosome number.
* (D) Turner’s Syndrome: Turner's Syndrome is another chromosomal disorder resulting from aneuploidy. It occurs due to the absence of one of the X chromosomes in females, leading to a karyotype of 45 chromosomes (44 + XO). This is a case of monosomy.

3. Conclusion:
Since only (B) Down's Syndrome and (D) Turner's Syndrome are caused by chromosomal aneuploidy, the correct combination is (B) and (D) only.