polytene chromosome
(Science: cell biology) giant chromosomes produced by the successive replication of homologous pairs of chromosomes, joined together (synapsed) without chromosome separation or nuclear division. They thus consist of many up to 1000) identical chromosomes (strictly chromatids) running parallel and in strict register. The chromosomes remain visible during interphase and are found in some ciliates, ovule cells in angiosperms and in larval dipteran tissue. The best known polytene chromosomes are those of the salivary gland of the larvae of drosophila melanogaster which appear as a series of dense bands interspersed by light interbands, in a pattern characteristic for each chromosome. The bands, of which there are about 5,000 in drosophila melanogaster, contain most of the dNA (ca 95%) of the chromosomes and each band roughly represents one gene. The banding pattern of polytene chromosomes provides a visible map to compare with the linkage map determined by genetic studies. Some segments of polytene chromosome show chromosome puffs, areas of high transcription.
Dictionary > Polytene chromosome
You will also like...

The Human Physiology
Physiology is the study of how living organisms function. Thus, human physiology deals specifically with the physiologic..

The Conscious & Unconscious Nervous System
This tutorial elaborates on how the nervous system works, particularly at the tissue level of the brain. There are three..

Amphibians & Early Reptiles
Obtaining air outside an aquatic environment required species to acquire suitable adaptations, and this was the case of ..

Takahē (Porphyrio hochstetteri)
Meet the colorful takahē, an extremely rare flightless bird. Find out more about its unique features and why they matte..

The Homo Species
The evolution of the species of the genus "Homo" led to the emergence of modern humans. Find out more about human evolut..

Plant Meristems and Growth
In plants, growth occurs in meristems, which are the site of repeated cell division of unspecialized cells. These cells ..