39. Turner syndrome results from
(1) Monosomy of sex-chromosome.
(2) monosomy of autosome.
(3) nullisomy of sex-chromosome.
(4) trisomy Of autosome.
Explanation:
-
Turner syndrome is typically associated with karyotype 45,X, meaning 44 autosomes plus only one X chromosome. This is a classic example of aneuploidy due to monosomy of a sex chromosome.
Option-wise explanation:
-
Monosomy of sex-chromosome – correct
-
Turner syndrome = monosomy X (45,X). One X chromosome is missing or partially missing in all or some cells, leading to characteristic features like short stature, gonadal dysgenesis, and primary amenorrhea.
-
Monosomy of autosome – incorrect
-
Monosomy for a full autosome (2n−1 for an autosome) is usually lethal in humans and is not Turner syndrome. Turner specifically involves the sex chromosome, not an autosome.
-
Nullisomy of sex-chromosome – incorrect
-
Nullisomy would mean both sex chromosomes are missing (0 sex chromosomes), which is not viable in humans. Turner patients have one X, not zero.
-
Trisomy of autosome – incorrect
-
Trisomies of autosomes (e.g., trisomy 21 = Down syndrome, trisomy 18, trisomy 13) involve an extra autosome, not the loss of a sex chromosome, and produce different syndromes, not Turner.
Thus, Turner syndrome specifically results from monosomy of a sex chromosome (usually X), so option (1) is correct.
