How different can a pair of chromosomes be?

Alan Smith alansmith at
Tue Nov 28 14:30:48 EST 2000


Check this review and paper by Scott Hawley.  Any papers from his lab should
be helpful.
	Requiem for distributive segregation: achiamsate segregation in Drosophila
females.  1993
	TIG  9(9) 310-317

	Direct evidence of a role for heterochromatin in Meiotic chromosome
segregation. 1996
	Cell ????
There are many papers published on the topic of chromosome pairing during
meiosis.  Starting with  Calvin Bridges thesis which appears as the first
article in the fist issue of Genetics published in 1916.

Looking at the work done in Drosophila, a certain threshold of
heterochromatin is required for pairing and explained in the review and
paper mentioned above.  In meiosis pairing and recombination are not
entirely related.  Think of the balancer chromosomes in fruit fly.
Chromosome size is irrelevant to pairing, (I think??) with a good level of
confidence.  I am not certain however if meiosis in Drosophila can be
considered a model representation of all meiotic machinery. Researchers can
get tiny little chromosome 4 in the fly to pair with the larger X chromosome
based on regions of heterochromotatin.  No percentage involved, just
identity in important regions for example heterochromatic regions in
Drosophila.  You can insert and delete all day as long as the region of
pairing is not destroyed.

Hope this helps
Alan Smith

P.S. I am no expert on this topic, but have read many papers for a genetics

-----Original Message-----
From: owner-methods at
[mailto:owner-methods at]On Behalf Of The Grouchybeast
Sent: Tuesday, November 28, 2000 7:22 AM
To: methods at
Subject: How different can a pair of chromosomes be?

My husband asked my a question I didn't know the answer to, so I thought
I'd ask here.

What degree of difference in size can be tolerated between two

For example, consider an insertion or deletion mutation which affects a
non-coding region of the chromosome.  How big an insertion or deletion
would it take to stop the chromosomes pairing up properly during cell
division?  Suppose there were many small insertions and deletions
scattered along the chromosome?

Obviously, there is some toleration of size difference within a pair of
chromosomes, but how much?  A percentage estimate would be nice (he's an
engineer, he likes numbers :-)

I see you standing there, far out along the way,
   I want to touch you but, the night becomes the day.
I count the words that I am never going to say,
   And I see you, in midnight blue.    (ELO - Midnight Blue)


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