Question

A disease caused by an autosomal primary non-disjunction is:

• A. Down's Syndrome
• B. Klinefelter's Syndrome
• C. Turner's Syndrome
• D. Sickle cell anemia

Answer 1

The correct option is A Down's Syndrome

Down's Syndrome is a chromosomal disorder caused due to the presence of an additional copy of chromosome 21 (trisomy of 21). This syndrome occurs as a result of an autosomal primary nondisjunction. Autosomal nondisjunction is the failure of homologous chromosomes or sister chromatids (autosomes) to separate properly during cell division.

Klinefelter's Syndrome (XXY) and Turner's Syndrome (XO) are caused by non-disjunction of sex chromosomes.

Sickle cell anaemia is a qualitative defect in globin chain synthesis due to the substitution of glutamic acid (Glu) by valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid results due to the substitution of a single base (point mutation) at the sixth codon of the beta globin gene from GAG to GUG.