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1/11/11
POISSON EQUATION
In class, we presented an example of two heterozygous parents (
D d
x
D d
) having a family of 3 tall and 1
dwarf offspring.
We calculated the probability of obtaining this family of 4 offspring using the binomial
equation.
As you know, given the parents, the probability of the tall offspring is 3/4, whereas it is 1/4 for the
dwarf offspring.
Thus, we expect both tall and dwarf offspring to occur at reasonably high frequencies.
In contrast, there are many “2outcome” problems in genetics, where the probability/frequency of one of the
two outcomes is very rare, even though the potential exists that one could observe a large number of these
events.
For example, a typical mutation frequency for a human gene is 10
5
mutations per gamete.
That is, a
mutation arises on average only once in this gene every 100,000 gametes.
In a collection of 1 million
gametes, the potential number of mutant gametes is large (theoretically, 1 million; that is, all gametes could
have experienced a mutation), even though the probability of a mutation is very small (10
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 Spring '08
 MARTA

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