[thedoc (OP)]

Mike Ogilvie  asked the Naked Scientists:
   1. During  recombination when the allele pairs mix for gamete creation, what is the degree of mixing? Is it a handful of switching segments for each chromosome? A few thousand?
2. During recombination, do the start and end points of a segment to be crossed always fall at the edges of genes, or at least at the edges of codons (so that the genes or codons remain contiguous)? Or is it completely random so that sometimes (probably often) the segments begin or end with a partial gene and/or codon?Thank you!-Mike Ogilvie

I have a Genetics question I've been wondering about for quite a while. It's actually a two-part question. I can't seem to find the answers anywhere.


 
What do you think?

[evan_au]

Q1. what is the degree of mixing? Is it a handful of switching segments for each chromosome? A few thousand?

It is very variable within the genome, and even between men and women.
But on average for humans, there is a crossover about every 100 million base pairs.

Human chromosomes have 50 - 250 million base pairs in length, so this suggests about 1 crossover per chromosome (if I have done the arithmetic correctly?).

Human chromosomes have 150-1100 protein-coding genes. Many genes on the same chromosome are inherited together. Geneticists use the unit "centiMorgan" to represent a 1% chance that two genes will not be inherited together (ie a crossover occurs between them); a centiMorgan is about 1 million base pairs.

See: http://en.wikipedia.org/wiki/Centimorgan#Relation_to_physical_distance
http://en.wikipedia.org/wiki/Human_genome#Molecular_organization_and_gene_content