Foetal sex is determined by examining cells from the amniotic fluid looking for
A. Chiasmata
B. Barr bodies and sex chromosomes
C. Only Barr bodies
D. Drumsticks

Hint: Amniotic fluid is the fluid present in the amnion. It is in this sac the foetus is present within the mother’s womb. The amniotic fluid can indicate the sex of the foetus, genetic anomalies and foetal infections.

Complete answer:
The amnion is a part of the extra embryonic membranes in which the growing foetus is present in the mother’s womb. The amnion is filled with the amniotic fluid. It acts as a shock absorber protecting the foetus from injury and mechanical shock, providing a medium for nutrient, gas and excretory product passage in between the mother and the foetus.
The amniotic fluid can also indicate the general health of the developing foetus and its viability. This is because the amniotic fluid contains metabolic wastes of the foetus and also its cells. The medical procedure of collection of amniotic fluid for testing is known as amniocentesis.
Barr bodies are inactivated X chromosomes present in the somatic cells of females. The Barr bodies are absent in males. The foetal cells obtained through amniocentesis are scanned for the presence of Barr bodies. If Barr bodies are present, the foetus will develop into a female and if Barr bodies are absent, the foetus is a male one.

Hence, the correct answer is option (C).

Note: Sex chromosomes are of two types – X chromosome and Y chromosome. Males have a genetic makeup of XY and females XX. However, in females one X chromosome is inactivated during embryogenesis. This is to prevent duplication of genetic information. This inactivated X chromosome is known as Barr body and is present only in females. It can be viewed easily as the condensed structure in somatic cells. The foetal sex can be determined by scanning foetal cells for Barr bodies.