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CpG Island length variation


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#1 Chris Harris

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Posted 25 May 2004 - 03:33 AM

CpG islands can be variable in length. Anyone know by what percentage range they can typically vary? I can't find much of any herlp on Google.
Cheers
Chris

#2 rassen

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Posted 25 May 2004 - 08:59 AM

Hi Chris,

Based on Gardiner-Garden's criteria, CpG islands are generally 500 bp in length [1]. Later, Jones et al [2] modified the criteria and suggested that regions of DNA of greater than 500 bp with a G+C equal to or greater than 55% and observed CpG/expected CpG of 0.65 were more likely to be associated with the 5' regions of genes and this definition excluded most Alu-repetitive elements.

If Gardiner-Garden's criteria is used, some CpG island can be as big as 1 kb, but there is a biphasic distribution with respect to CpG island length, with a significant proportion of CpG islands being in the small region of 200-400 bp [2]

References
[1] M. Gardiner-Garden, and M. Frommer, CpG islands in vertebrate genomes, J Mol Biol 196 (1987) 261-282.
[2] D. Takai, and P. A. Jones, Comprehensive analysis of CpG islands in human chromosomes 21 and 22, Proc Natl Acad Sci U S A 99 (2002) 3740-3745.

Hope thtat helps.

Edited by rassen, 26 May 2004 - 01:55 PM.


#3 Chris Harris

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Posted 26 May 2004 - 12:19 AM

Thanks Rassen,
I now realise my question was poorly phrased. What I meant was: is there evidence to suggest that the CpG island for a particular gene can vary in length between individuals/breeds/species?
Cheers
Chris

#4 rassen

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Posted 26 May 2004 - 01:54 PM

Hi Chris,

As stated in Gardiner-Garden and Frommer's original paper, CpG islands are not always conserved between species and vary in the position, length or stength a CpG island.

But, I don't think there are much variations among individuals unless there are genetic changes such as repeat sequences.




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