Dictionary > Polytene chromosome

Polytene chromosome

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.


You will also like...

Population Regulation in an Ecosystem
Population Regulation in an Ecosystem

With regard to the population size of a species and what factors may affect them, two factors have been defined. They ar..

Early Earth
The Origins of Life

This tutorial digs into the past to investigate the origins of life. The section is split into geological periods in the..

vitamins
A Balanced Vitamin Diet – Vitamins A – K

A balanced diet is essential to a healthy organism. Insufficiency or too much of a particular element or compound, such ..

Still freshwater and plants
Still Freshwater & Plants

Plants in lentic habitats have features not found in terrestrial plants. They acquired these features as they adapt to t..

Lights' Effect on Growth
Lights’ Effect on Growth

This tutorial elaborates on the effect of light on plant growth. It describes how different plants require different amo..

Chromosome Mutations
Chromosome Mutations

Mutations can also influence the phenotype of an organism. This tutorial looks at the effects of chromosomal mutations, ..