Re: frequency of crossovers at meiosis

On Feb 19, 2:19 pm, psl...@xxxxxxxxx wrote:
I read that mendels second law (saying that traits are inherited
independently) if either

1) the genes regultating the traits reside on different chromosones
2) the genes are far from each other on the same chromosone

Can this really be true for 2) ?
If even nr of crossovers (including 0) is as common as odd, the traits
are more likely to follow each other than if the genes are at separate
chromosones.

Am I thinking about this wrong ?

Number 2 is true only if the total probability per generation of
cross over, for the entire chromosome including every gene on the
chromosome, is high. Maybe the article you are reading is assuming
this. It doesn't sound implausible to me, but that is the implicit
assumption of number 2.
Note that the total rate of crossover can be quite high, and even
be 1, while the probability of two nearby genes being split by a cross
over is quite low. When two genes in adjacent loci are split by a
cross over, all the genes on each side of this pair are split. The
probabilities of adjacent pairs splitting up add up for all the genes
intermediate between two far away chromosomes. If there are a lot of
genes between the two chromosomes, the total probability can get quite
high.
So I think the implicit assumption is simply that each chromosome
is split by crossover about once every generation. Many of the genes
on the same chromosome will not be inherited independently, but a lot
will be inherited independently. I don't know if this is true for each
and every eukaryote, but it may be.

.

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