Question

In mongolism/Down’s syndrome the patient has
A. Barr body
B. Trisomy
C. Monosomy
D. Nullisomy

Answer 1

Hint: Down syndrome or mongolism is by far the most common and best known chromosomal disorder. It is primarily caused by the presence of all or part of a third copy of chromosome 21.

Complete answer:
Down syndrome is the best known chromosomal disorder in humans and the most common cause of intellectual disability. It is primarily caused by trisomy of chromosome 21 and this is the most common trisomy among live births. It is characterized by certain birth defects, learning problems and facial features. Like other chromosomal disorders, trisomy 21 also gives rise to multiple systemic complications as part of the clinical syndrome. This chromosomal disorder leads to both structural and functional defects in patients with Down syndrome. A child suffering with Down syndrome also may have heart defects and problems with hearing and vision.

Among the given options:
The Barr body is the inactive X chromosome found in female somatic cells. Human females contain two X chromosomes, while males have one X and one Y chromosome. In all the female somatic cells that don’t take part in sexual reproduction, one of the X chromosomes is active, and the other is inactivated through a process called lyonization, becoming the Barr body.
Monosomy refers to the condition of having a single copy of a chromosome pair instead of the usual two copies found in diploid cells. Monosomy causes some known human diseases like Turner syndrome and Cri du Chat syndrome.
Nullisomy is a genetic disorder which involves the absence of both the normal chromosome pairs for a species (2n-2). It is caused by nondisjunction, during meiosis that causes two of the gametes to have no chromosomal material, leaving the other two gametes to have double the amount of chromosomal material.

So, the correct answer is option B.

Note: Down syndrome, trisomy 21, or (formerly) mongolism, is a congenital disorder caused by the presence in the human genome of extra genetic material from chromosome 21. Here, the affected individual may transmit an extra part of chromosome 21 or an entire extra copy of chromosome 21.