How aneuploidy deldtion and duplication cause genetic imbalance?
Answers
Polytene chromosomes are formed by repeated rounds of DNA replication without any cell division (endomitosis). These commonly occur in the salivary glands of Drosophila (and other dipterans) although the rest of the insect body contains normal diploid cells.
As compared to the normal chromosomes, the polytene chromosomes are much larger in size, and thus, they show a much higher number of bands. The dark bands represent the heterochromatin regions, while the light bands represent the euchromatin regions.
These bands are used as genetic markers. The banding pattern is specific for the particular chromosome of a particular species. Moreover, being larger in size, they are much easier to observe, than the normal chromosomes.
So, if there is any alteration in the chromosome, due to deletion, or duplication, it will be much easier to detect in the polytene chromosome, owing to their large size, and typical banding patterns. That is why the polytene chromosomes are useful for studying the chromosomal structure as well as any alterations in chromosomal structures.
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