Question

Explain briefly the cytological mapping of chromosomes of Drosophila.

Answer 1

 CYTOLOGICAL MAPPING OF CHROMOSOMES OF DROSOPHILA :

• About 5000 single cross bands have been noted on the four pairs of salivary gland chromosomes in D. melanogaster.
• This number is considered a minimum approximation of the number of genes in that animal.
• Some genes have been associated with individual bands. Bridges system of designating parts of chromosomes with numbers, subdivisions with letters, and numbering bands within subdivisions had made it possible for investigators to discuss precise locations.
• In this system, fairly uniform divisions are numbered in order throughout each entire chromosome set from 0 at the beginning of the X chromosome to 102 at the end of chromosome 4.
• Subdivisions within the areas are identified with letters from A to F, and bands within subdivisions are numbered from left to right.
• For example, the gene (w) for white eyes is in bands 3C2. In linkage units this gene is located at 1-5 in the X chromo some.
• Linkage data do not correspond exactly with cytological locations, but the linear sequence of genes can be verified from salivary preparations.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          

Chromosome Mapping:

• The mapping of genes located on a chromosome is referred to as Chromosome mapping.
• It is represented as an idiogram.
• It tells the position of individual genes on chromosomes.
• Italso helps in determining the chromosomal abnormalities.
• The Human Genome Project (HGP) provides a detailed map of all the human chromosomes.