Q.7 The number of “Barr Bodies” present in a somatic cell of a woman suffering
from Turner syndrome is ____.
(A) 0
(B) 1
(C) 2
(D) 3
Barr Bodies in Turner Syndrome: Number in Somatic Cells Explained
The correct answer is (A) 0. Women with Turner syndrome have no Barr bodies in their somatic cells due to the absence of a second X chromosome.
What Are Barr Bodies?
Barr bodies represent inactivated X chromosomes in female cells, ensuring dosage compensation between XX females and XY males. The number of Barr bodies equals the total X chromosomes minus one. In typical human females (46,XX), one Barr body forms per somatic cell nucleus.
Turner Syndrome Genetics
Turner syndrome features a 45,X karyotype, with only one X chromosome and no Y. Somatic cells lack a second X to inactivate, resulting in zero Barr bodies. This monosomy causes symptoms like short stature and ovarian dysfunction but directly explains the Barr body count.
Explanation of All Options
| Option | Barr Bodies | Reason |
|---|---|---|
| (A) 0 | Correct | Matches 45,X karyotype; no extra X for inactivation |
| | ||
| (B) 1 | Incorrect | Occurs in normal 46,XX females |
| | ||
| (C) 2 | Incorrect | Seen in triple X syndrome (47,XXX) |
| | ||
| (D) 3 | Incorrect | Rare in tetrasomy X (48,XXXX); not relevant here |
| |
