politenic chromosomes?

[rui_benfeitas]

Can someone please tell me what they are used for? I know a politenic chromosome only exists in some dipters and it is the result of replication in cells that doesnt divide (am I correct?). But dont know what they can be used for in laboratorial technics...
Please help

[LilKim]

You're correct, polytene chromosmes are the result of several rounds of DNA replication without cell division...in cells that do not divide (they 'die-off' when they get old).

These regions of DNA occur at specific genes that are very transcriptionally active (resulting in the production of lots of RNA and most-times subsequent protein production)

Because of the high level of transcription, it is often easy to study transcriptional-control/regulation and transcriptional-event ( initiation and termination of trasncription) in organisms containg these 'giant' chromosome.

Hope this helps!
- KIm

[LilKim]

also I believe that Polytene chromosomes are useful in mapping studies ... to determine the specific location of genes based on the morphology (banding pattern) of these chromosomes.

But i don't really know much about this stuff "off the top of my head"... hope this stuff helps as a starting point
- KIm

[rui_benfeitas]

Yeah!
It was of great help! It was a doubt I had before an exame I did and, altough I wasnt asked to tell anything about politenic chromosomes, it really was great to understand finally why they are used.
And yes, they really are used in some technics where they are used as "more natural" ways of figuring out the map (just like the FISH technic) - dont know more though... But this information is enough for now. Thanks a lot!

[Locus]

By using polytent chromosomes it is easy to recognise duplication or diletion of the relatively large part of chromosoms (whoul genes and, may be, things such introns and exons)., becouse those chromosomes thik and disk of chromatin density, that associates with the genes (not all aff them) is easy to recognition