Chromosomal disorders Questions in English

(D) Down's syndrome is an example of aneuploidy of autosome.
Down's syndrome is a genetic disorder caused by the presence of an extra copy of chromosome number $21$ (trisomy $21$).
Since chromosome $21$ is an autosome,this condition is classified as an autosomal aneuploidy.
It occurs due to the nondisjunction of chromosomes during meiosis,leading to a cell having $47$ chromosomes instead of the normal $46$.

(A) . Klinefelter's syndrome.
Gynaecomastia,which is the development of enlarged breast tissue in males,is a characteristic symptom of Klinefelter's syndrome.
Klinefelter's syndrome is a genetic condition caused by chromosomal aneuploidy where males possess an extra $X$ chromosome,resulting in an $XXY$ genotype.
This condition leads to symptoms such as reduced testosterone levels,small testes,reduced fertility,and the development of female-like secondary sexual characteristics,including gynaecomastia.

(A) The correct answer is $A$.
$1$. When a sperm with $22A + XY$ fertilizes a normal egg with $22A + X$,the resulting zygote has a chromosome composition of $44A + XXY$. This condition is known as Klinefelter's syndrome.
$2$. When a sperm with $22A + O$ fertilizes a normal egg with $22A + X$,the resulting zygote has a chromosome composition of $44A + XO$. This condition is known as Turner's syndrome.

(B) The condition where an organism has one extra chromosome in one of its homologous pairs is called $Trisomy$.
In this state,the chromosome count becomes $2n + 1$.
$Monosomy$ $(2n - 1)$ refers to the loss of one chromosome from a pair.
$Nullisomy$ $(2n - 2)$ refers to the loss of both chromosomes of a homologous pair.
$Polyploidy$ refers to an increase in the number of entire sets of chromosomes (e.g.,$3n, 4n$).