Question

In human beings, 45 chromosomes with single X/XO abnormality cause ________.

• A. Down syndrome
• B. Turner syndrome
• C. Klinefelter syndrome
• D. Edward syndrome

Answer 1

The correct option is B Turner syndrome

• Down syndrome is trisomy of 21, i.e., presence of chromosome 21 in three copies. The affected individuals are mentally retarded, short in stature, and have a broad, short skull; low-set ears, smallmouth, hyper flexibility of joints; and excess skin on the back of the neck, epicanthic skin fold above the eyes, and transverse palm crease.
• The presence of one or more extra copies of X-chromosome in males causes klinefelter syndrome. The affected individuals have 44+ XXY/44+XXXY/44+XXXXY chromosomes and carry some feminine characters. They are sterile feminised males with enlarged breasts.
• Turner syndrome is monosomy caused by the absence of one copy of X-chromosome from females (45+XO). These females carry the only single copy of genes present on X-chromosomes and hence are sterile females.
• Trisomy of the ${18}^{th}$ chromosome causes edwards syndrome (45+XY/45+XX) leading to severe physical birth defects in infants. The surviving infants have profound mental retardation.

Thus, the correct answer is B.