# How many recombination events are there per generation in humans?

I'm looking for a reference that tells me how many recombenation events occur in humans from one generation to the next. Assuming that the human genome is a 3.3 GigaBases long DNA sequence, how many recombination events do you find, and what is he amount of DNA exchanged? Is it in the order of 0.1%, 1% oder 10%?

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This is not easy to answer, since it depends on a number of factors. For example it is dependent on the region of the genome (there are hotspots). I found a PhD thesis, which goes into the details here and which also has a ton of interesting references:

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Back-of-the-envelope calculation

The definition of the centimorgan is that it is the length of DNA in a chromosome corresponding to a 1% chance of crossover occurring.

In human chromosomes 1 cM = approx. 1Mbp.

Your value for the length of DNA in the genome = 3.3 Gbp = 3300 MBp

Ignoring complications like the Poisson distribution:

If 1 cM = 1% chance of crossover, there will be on average 1 crossover per 100 cM or per 100Mbp

Therefore crossovers per human genome = 3300/100 = 33 or approx 1-2 per chromosome

This seems rather small but wait, there are data...

Actual data

This Table, taken from here shows the number of chiasmata by chromosome for 8 human cells. (Note that it believed that there has to be at least one chiasma per chromatid pair since they have a structural role.)

The average chiasmata per chromosome for each chromosome can be estimated by dividing the number in the final column by 8. These vary from (rounding aggressively) 3.5 for Chr 1 and Chr 2, to 1 for Chr 20. So my back-of-the-envelope calculation seems to have produced a reasonable answer.

What is the amount of DNA exchanged? I'm not sure this question matches well with the picture that emerges from these numbers.

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