Chromosome analysis or karyotyping
1. Chromosome banding. Casper Sun 1968 and others found fluorescence exhibited distinctive sequence of bands. Best chromosomes are visible during metaphase of mitosis cell division. So analysis is done from cells taken from dividing tissues like bone marrow for induced inter division in culture. Like phytohemagglutinin.
Chromosomes are held in metaphase by adding colchicine. It prevents polymerization of spindle fibres of cell division.
Salt solution is added to swell and disperse chromosomes. Then there fixated. Then they are stained for banding patterns. Basically four types of procedures
• Q banding for quinacrine fluorescence banding. Fluorescent bands observed which are rich in A-T bases.
• G banding. Some band appear dark stained. Bands of your due to compaction of chromatin by non histone proteins.
• c banding. Centromeric banding. removes much of non histone and histone proteins. Centromeric regions of 1, 9, 16 and y chromosomes are stained. C band positive regions are concentration of Satellite DNA.
• R banding. Reverse banding. Heat treatment saline heat treatment prior to giemsa staining. Reverse of g banding.
Chromosome are arranged in sequence of length and Eid centrally situated centromere is placed first.
Banding is specific to each chromosome and helps us study them like transmission of a chromosome from one generation to next.
2. Flow cytometry. Fluorescent activated cell sorting. cells are ruptured and stained with fluorescent dye which selectively stains the chromosome. Then chromosomes are projected through a flow chambers across a laser beam - causing chromite to floresce. This is rapid karyotyping.
3. Somatic cell hybridization. hybrids of somatic cells like human and mouse can be produced. Possible to study proteins produced by chromosomes retained in the hybrid.
4. fluorescence in situ hybridization. Fish technique is used to find number of copies of segment in DNA and structural abnormalities like down syndrome.
5. Chromosome microarray analysis.
now virtual karyotyping and automated tools are used with computers and advanced sensors.
Application. Pregnancy abnormalities in the the foetus. Tracing abnormality in the family. Looking for abnormality is in person for cancer. Studying chromosomes inheritance and behaviour. Genetic screening
Cytogenetics is study of chromosomes.