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 “2-outcome” 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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