Re: Genomic Instability?

Perplexed in Peoria wrote:
"Alan Meyer" <ameyer2@xxxxxxxxx> wrote in message news:er2i9t$m9q$1@xxxxxxxxxxxxxxxxxxxxxx

If I remember
correctly, in eukaryotes (or maybe it's just mammals?) the
uncorrected mutation rate is about 10 to the minus 9. That's 3
mutations in 3 billion base pairs that make up a human gamete.

My memory says it is about 20 times as large.

Of course that rate is significant, and it would be even larger
in some situations, like organisms living near sources of
radiation.

To the best of my knowledge however, chromosomal crossovers are
actually much more common. Every chromosome requires at least
one in order to complete meiosis, and IIRC the average is around
2.5. For humans with 23 chromosomes that gives us an average of
57.5 crossovers per gamete.

My memory says about 35 crossings-over. And it is not the case that
each chromosome requires one. I suspect that you got your figure
by adding 23 chromosomes to 35 crossings-over to get about 57.5
'genome pieces' which independently segregate.

In case it helps:

"Patterns of Meiotic Recombination in Human Fetal Oocytes"
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=379134

.....gives averages of 70 crossovers in the female and 50 in the male
for a total of 120 crossovers per individual per generation.

"Estimate of the Mutation Rate per Nucleotide in Humans"

http://www.genetics.org/cgi/content/full/156/1/297

.....gives 175 mutations per generation.

To address the original: "In fact, the number of point mutations
per generation in humans is a couple times larger than the
number of crossings-over." - table 4 in that paper gives
estimates of the mutation rate for different classes of
mutation. Around 90% appear to be SNPs.
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