Best sample for DNA karyotyping -

Ans. is 'a' i.e., Blood* Karyotyping is the study of number and appearance of chromosomes* The first step in karyotyping is sample collection* Sample utilized are# Blood# Bone marrow# Amniotic fluid* Most commonly used sample is blood. Blood is centrifuged. WBCs are separated. White Blood cells are rapidly dividing cells with DNA.* The cells are grown in culture.* During cell cycle, only in M phase of cell cycle, the chromosomes are highly condensed. Hence, metaphase arrest of the cells are mediated using drugs like Colchicine.* The cells are lysed using hypotonic solution.* The chromosomes that are released are stained with Giemsa.* The following features are observed:# Differences in basic number of chromosomes - to detect aneuploidy or trisomy# Differences in absolute sizes of chromosomes - to detect DNA duplication or deletion# Differences in the position of centromeres to detect translocations.# Differences in degree and distribution of heterochromatic regions. Heterochromatin is functionally inactive reghion of a chromosome. It stains darker than euchromatin.* Bone marrow is used as a sample for karyotyping to detect acquired chromosomal aberrations in blood malignancies* Amniotic fluid karyotyping is done only in cases of repeated miscarriages or if copy number variations of chromosomes are highly suspected in the fetus.