Location of Genes - Chromomeres

Location of Genes - Chromomeres - The location of genes: chromomeres. In 1928 Belling suggested that the chromomeres, which appear like a series of granules on the chromosome, might be the genes. Although the view received little support at that time, some recent work tends to support the view that the chromomeres represent the sites of genes. Whole mounts of meiotic chromosomes show chromomeres under the electron microscope

The chromosomes consist of axial filaments from which arise chromatin fibre loops. In the region of the chromomeres there is increased density in the attachment of the loops to the axial filaments. Callan and Llyod (1960) have suggested that each loop of lampbrush chromosomes is correlated with the activity of a gene. According to them the loop may possibly contain several identical 'slave genes' controlled by a 'master gene' .Thomas (1969) has also suggested that each chromomere represents a functional gene, i.e. a master gene with many slave copies.

Beerman's (1967) work on mutations supports the view that in polytene chromosomes the dark bands (which represent transverse rows of chromomeres) correspond to genes. It has, however, been pointed out by Watson (1970) that the interband region of polytene chromosomes must also contain genes.

Thers is, however, no one to one correspondence between chromomeres and gene. For example, it has beed estimated that the total number of chromosomes in one set of chromosomes of amn is at the most 600. the total number of known mutations in man is , howver much greater than this ( McKusik, 1971). thus the view that each chromomere represents a functional gene is not tenable.

The first picture of an gene was published by sahpiro and co workers in 1969. They chemically purified the lac operon of DNA and photographed it with the help of an electron microscope