Re: Minimum number of males in a breeding population


Dunc Harris wrote:
Or if you want to see it in graphical form, see:

http://static.flickr.com/53/120832509_dfd722136c_o.png

what I made.

A graph of effective population size for absolute populaiton size
N=10000 and varying Nos of males. The second half of the graph for
N>500 males not shown is a mirror image of this side.

All you have to do now is decide what the minimum allowable effective
population size is and take a reading off the graph there. When there
are few males, an extra male increases Ne quite a bit, but the more
males there are the less this effect -- up to 5000 of course, after
which there are too few females and so Ne decreases again.

However, the graph fails to take into account other factors that affect
Ne such as, non-overlapping age structured populations and Unequal
contributions to the next generation.

As you indicate it isn't that simple. How many males produce males in
the next generation, where the number of males is again 1:10. You are
talking about around 10% of the population accounting for half the
genetics, and this happens every generation.

If effective population size was calculated using a single snap shot
generation the Holstein population would have an effective population
size of hundreds of thousands, but you have to deal with facts that one
AI sire in the past can be responsible for over 1/5 the genetics of the
current population. Back in 1992, when I was working on this junk,
Chief accounted for 1/5 the genetics of the elite population he had a
son that by 1992 had sired 1/4 of the top 400 bull studs in the then
current registry, and Mark had brothers. Mark was literally leaving
his own mark on the genetics of the population, but half his genetics
were already set as 1/5 the genetics of the population due to his dad.

Ron Okimoto

.

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