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.
Blood
Bone marrow
Amniotic fluid
Chorionic villi
Molecular Genetics