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turns out that genetic diversity in the species is less than modeled, genetic
diversity decrease due to loss of unique alleles should be less than predicted
by the modeling. In many cases, it is the preservation of low-frequency,
not high-frequency, alleles that will maintain the evolutionary potential
of a species.
This is not to say that loci with higher allele frequencies or lower
numbers of alleles are not of interest (e.g., modeling population genetics
of SNPs or loci with a few common alleles). In one sense, even in situations
where there are multiple copies of one allele, each copy can be thought
of as being “unique” and at risk of loss. Observing how lower-frequency
alleles change in frequency through generations can help us understand
how allele frequencies may shift when less diverse loci are involved. As
will be discussed in the concluding chapter, the loss of copies of a particular
allele of higher frequency at given loci by spationumeric effects such as
those explored in this topic for the loss of lower-frequency alleles can have
profound effects on the probability of certain combinations of alleles from
different loci that interact to affect traits in a multilocus fashion (and see
Templeton 2006).
Summary and Conclusions
Our main fi ndings thus far with regard to the population and genetic edge
effect conditions outlined above are as follows:
1. Populations initiated from founders placed nearer borders can grow
at slower rates.
2. Populations initiated with founders nearer borders can lose
heterozygosity (observed or expected) at a faster rate, and in the
cases here, the founders have to practically be at the border to see an
increased heterozygosity loss rate.
3. Populations initiated with founders nearer borders can experience less
inbreeding (as indicated by F values).
4. Differences in the number and frequencies of unique alleles available
per locus have only slight effects on rates of change in levels of
heterozygosity relative to placement of founders with regard to borders,
although the absolute values of heterozygosity differ between trials
that are identical except for allelic diversity per locus (Fig. 8.16).
5. Differences in the number and frequencies of unique alleles available
per locus can have a pronounced effect on unique alleles retained by
populations initiated with founders at different distances from preserve
borders. When alleles are numerous and at low frequencies, loss of
unique alleles can offer a sensitive measure of population genetic
effects driven by differing initial conditions among trial populations
(e.g., founder placement relative to borders).
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