[geeks] Genetic probabilities and chickens

[Joshua D Boyd]

In bio class, we had a problem between 2 chickens where there was a
gene (lets call its dominated gene I and its recessive one i) where
the father was known to be homozygous resesive and all the chicklets
produced expressed the recessive trait.  So, the professor argued that
this meant that the mother must also be homozygous recessive.  

I argued that it didn't mean that unless the two chickens had an
infinate number of babies since if the mother was heterozygous, there
was a 1/2 chance of any one baby being homozygous recessive.  For
any 2 babies, there would be a 1/4 chance, any three 1/8, and in
general for any n babies a 1/(2^n) chance of them being homozygous
resessive. 

So, without going too far into statistically expressions of truth, the
possibility of the mother being heterozygous lies in how many
chicklets she is likely to have with a particular male.  And now I'm
wondering, exactly how many is she likely to have?  My impulse would
be that should wouldn't be too likely to have more than 10 or 20, and
1/2^20 is still a large enough chance that given the size of the world
it probably happens fairly regularly.


-- 
Joshua D. Boyd