Question

$XXY$ chromosome constitution is represented by

• A. Downs syndrome
• B. Turners syndrome
• C. Klinefelters syndrome
• D. None of the above

Answer 1

Answer: (C)

Klinefelter's syndromes are trisomics for sex chromosomes $(2 X +1)=47$. Commonly they inherit $2 A + XXY$ chromosomes. They are genetically male due to presence of $Y$ chromosome but the testes remain under developed and fail to produce sperms hence, these are sterile. often breasts develop (gynaecomastia) and there may be some mental retardation.
Turner's syndrome inherit a single $X$-chromosome instead of two sex chromosomes, ie, these are monosomics for sex chromosomes $(2 X -1$ or $2 A + XO )$. These syndromes are sterile female.
Down's syndrome is autosomal abnormality due to trisomy of $21^{\text {st }}$ chromosome. Thus, a Down's syndrome illustrates autosomal aneuploidy. The phenotype of this syndrome is short statured and feeble-minded child who does not usually survive the first year after