Question

In Down's syndrome of a male child, the sex complement is
A. Xo
B. XY
C. XX
D.XXY

Answer 1

Hint: Downs syndrome is a genetic disorder, it is also called trisomy 21, which is due to the presence of partial or full chromosome on the 21 chromosome of the autosome, this condition causes mental retardation and developmental delays.

Complete answer:
Down's syndrome is due to the presence of three genes on chromosome 21.
In normal conditions, one chromosome consists of 2 genes, but here in this condition, during cell division, either disjunction or sometimes a small amount of extra copy may present due to improper cell division and this happens on chromosome number 21.
The child affected with down's syndrome is usually genetically normal.
If parents have a history of down's syndrome with one child, there are chances of 1% to have a second child with the same.
The female with down’s syndrome have 47 XX and the male with down's syndrome have 47 XY.
Down's syndrome does not have any link with sex chromosomes, they are due to defect occur in autosomes.
Sometimes, all of the cells do not have trisomy on 21 chromosomes, only some cells only possess It, and this condition is called Mosaic down's syndrome.
Down's syndrome also occurs due to translocation proposed by Robertsonian.

So the correct option is XY, because down's syndrome, won’t relate anything to sex chromosomes, so the sex complement is XY.

Note:
The child with down's syndrome usually has dementia, it is mainly due to more production of amyloid-beta peptides, similar to Alzheimer’s disease. And they produce fewer lymphocytes and less antibodies, this makes them more disease prone.