KARYOTYPE

• External morphology of Chromosomes specific for each species of living organisms.
• Karyotype can be studied in metaphase of mitosis.
• Karyotype includes the number of chromosomes, relative size, position of centromere, length of the arms, secondary constrictions and banding patterns.

BANDING TECHNIQUE

• It is used to study the specific pattern of bands and interbands on chromosome.
• This includes the use of fluorochromes (fluorescent dyes).
• Chromosomal banding was discovered by Casperson.

(i) Q-banding : It is obtained when chromosomes are stained with quinacrine mustard. It stains A- T rich area.

(ii) G-banding : Chromosomes are stained with Giemsa. It stains sulphur rich protein parts.

• A variety of different bands are obtained by the modification of Q-banding and G-banding like C, R, T and N-bands. Other techniques used in karyotype preparation are FISH (Fluorescence in Situ Hybridisation), Mc FISH (Multicolour fluorescence in situ Hybridisation) and flow cytometry.

USE OF KARYOTYPING

(i)      It suggests primitive or advanced features of an organism. If karyotype shows a large size difference between the smallest and the largest chromosome of the set and having fewer metacentric chromosomes is called assymetric karyotype, which is a relatively advance feature.

(ii)     The karyotype of different species are compared and simillarities in them represent the evolutionary relationships.

(iii)    Karyotype is helpfull in detection of chromosomal abberrations.

IDIOGRAM

Diagrammatic representation of Karyotype. In idiogram chromosomes are arranged in decreasing order of size.

Sex chromosomes are placed in last but in idiogram of Drosophila sex chromosomes are placed first. Idiogram is specific for every species so it may be used in criminal investigation by forensic experts.