Assertion: Foetal disorders can be diagnosed by chorionic villi sampling.

Reason: Karyotyping can be done for mitotically dividing cells of chorionic villi.

The correct option is A Both assertion and reason are true and reason is the correct
explanation of assertion
The chorion is the outermost fetal membrane around the embryo in humans. Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood.

Karyotyping is a test to examine chromosomes in a sample of cells. This test can help identify genetic problems as the cause of a disorder or disease. For prenatal diagnosis, amniotic fluid or chorionic villus specimens are used as the source of cells.

The process of generating a karyotype begins with the short-term culture of cells derived from a specimen. After a period of cell growth and multiplication, dividing cells are arrested in metaphase by addition of colchicine, which poisons the mitotic spindle. The cells are next treated with a hypotonic solution that causes their nuclei to swell and the cells to burst. The nuclei are then treated with a chemical fixative, dropped on a glass slide, and treated with various stains that reveal structural features of the chromosomes.