Question

A disease caused by an autosomal primary nondisjunction is
A) Sickle Cell Anemia
B) Down’s Syndrome
C) Klinefelter’s Syndrome
D) Turner’s Syndrome

Answer 1

Hint: The disease is related to the trisomy of a certain chromosome out of the 46 pairs of chromosomes in the human body.

Complete answer:
Down’s Syndrome is caused due to trisomy of the 21st pair of chromosomes due to autosomal primary nondisjunction. It was discovered by Langdon Down and was named after him.
The main symptoms of Down’s Syndrome are as follows:
1) Broad Forehead
2) Permanently open mouth with protruding tongue
3) Rounded face, also known as Moonface
4) Projecting lower lip
5) Mongolian types eyelid fold
6) Vertical fold epicanthus on either side of the nose
7) Stubby Fingers
8) Broad palm with a characteristic palm crease
9) Short neck
10) Low intelligence due to mental retardation
11) Underdeveloped and immature gonads (testes and ovary)

Additional Information:
Examples of some other autosomal diseases caused by nondisjunction are:
Edward’s Syndrome: It occurs due to the trisomy of the 18th pair of the chromosome. A person with Edwards syndrome has tightly clenched fingers against the palm. Mentally retarder and also usually dies within six months of birth.
Patau’s Syndrome: It happens due to the trisomy of the 13th pair of the chromosome. The patient shows cleft lip and palate, deformed ears, and small chin.
Cri du chat syndrome or Cat Cry Syndrome: It occurs due to the deletion of the short arm of the 5th chromosome. The newborn affected cries like a meowing cat, and hence it is known as Cat Cry Syndrome. Or Cri Du Chat syndrome.

So, the correct answer is, “A disease caused by an autosomal primary nondisjunction is Down’s Syndrome.”

Note: It should be remembered that Down’s syndrome occurs due to the nondisjunction of the 21st pair of the chromosome during the anaphase of the cell cycle. Klinefelter’s and Turner’s syndrome are sex chromosomal disorders.