-Karyotyping.

Karyotyping

Def: studying chromosomes in a form suitable for analysis during metaphase or Chromosomes are stained and visualized under a microscope.

Steps:

1.  As chromosomes are only visible microscopically in dividing cells (metaphase chromosomes)

2.     Chromosome analysis involves taking some non-dividing cells (usually peripheral blood lymphocytes)

3.     Culturing them to encourage cell division on certain media.

4.     Arrest of cellular division in metaphase.

5.     Adding hypertonic saline leading to bursting of cells & release of chromosomes.

6.     Staining which creates unique banding patterns on the chromosomes and subsequently examines the cells under microscopy for any extra or missing chromosomes, or large scale structural chromosomal abnormalities.

This method will miss any changes smaller than 5–10 megabases (5–10 million bases) in size, so is unsuitable for the detection of most microdeletions or duplications.

Along with array comparative genomic hybridization it is helpful in identifying changes in amount of genetic material – gene copy number variation (CNV) including duplications (increased copy number) and deletions (decreased copy number), so they are useful Investigate broad/complex phenotype.