Question

Down syndrome is caused due to
A. Bacterial infection
B. A chromosomal abnormality
C. Viral infection
D. Lack of oxygen supply to the brain during birth

Answer 1

Hint:
Chromosomes are always in pairs and the absence or excess or abnormal arrangement of one or more chromosomes will cause chromosomal diseases. There are 46 chromosomes (23 pairs) in a normal human being, out of 23 pairs 22 pairs of chromosomes are autosomes and 1 pair is of sex chromosome. Trisomy (an additional copy of a chromosome) or monosomy (lack of one copy of a chromosome in a pair) leads to serious consequences in individuals.

Complete step by step solution:
An absence or excess or abnormal change in the abnormal arrangement of chromosomes in individuals will lead to chromosomal disorders such as down's syndrome, Klinefelter's syndrome or Turner's syndrome. Down's syndrome is caused due to the presence of an additional copy of chromosome number 21. This is referred to as trisomy of 21. The disease is named after the person that first described this disorder i.e Langdon Down. The person suffering from Down's syndrome is short-statured with a small round head, furrowed tongue and partially open mouth, the palm of the person is broad with characteristic palm crease. The physical, psychomotor and mental development is retarted. The person also suffers from congenital heart disease.
The following picture shows the chromosome arrangement of an affected individual:

Hence, down's syndrome is caused due to chromosomal abnormality.
Thus, the correct answer is Chromosomal abnormality.

Option ‘B’ is correct

Note:
Down's syndrome can be diagnosed after or before birth. It can be diagnosed by a technique called amniocentesis during which the amniotic fluid is taken out with the help of a needle and then karyotyping is done in the lab and if any abnormality is seen during karyotyping, the foetus is aborted. Once, birth is given there is no cure for this disorder.