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INBREEDING DEPRESSION WITH HETEROZYGOTE ADVANTAGE AND ITS EFFECT ON SELECTION FOR MODIFIERS CHANGING THE OUTCROSSING
D Charlesworth1, B Charlesworth1
1Department of Ecology and Evolution, University of Chicago, 915 E. 57th St., Chicago, IL, 60637.
Summary
Inbreeding depression can be higher in partially selfing populations. Modifier alleles increasing selfing may not fix in these populations due to genetic associations and increasing inbreeding depression.
Area of Science:
- Population Genetics
- Evolutionary Biology
- Quantitative Genetics
Background:
- Inbreeding depression, the reduced fitness in offspring from mating related individuals, is a key factor in evolutionary processes.
- Heterozygous advantage, where heterozygotes have higher fitness, can maintain genetic variation but also contribute to inbreeding depression.
- Selfing (self-fertilization) rates significantly impact genetic diversity and the expression of inbreeding depression.
Purpose of the Study:
- To investigate the equilibrium level of inbreeding depression in populations with varying selfing rates.
- To analyze the influence of heterozygous advantage at multiple, partially linked loci on inbreeding depression.
- To examine the conditions under which modifier alleles that increase selfing rates can invade and spread within populations.
Main Methods:
- Mathematical modeling of population genetics.
- Analysis of symmetrical and asymmetrical heterozygous advantage at several partially linked loci.
- Study of the spread of modifier alleles affecting selfing rates.
Main Results:
- Inbreeding depression can be higher in partially selfing populations compared to outcrossing populations, even with heterozygous advantage.
- The spread of alleles that increase selfing is contingent on the level of inbreeding depression.
- In partially selfing populations, smaller levels of inbreeding depression (less than one-half) can prevent the fixation of selfing-increasing alleles, unlike in fully outcrossing models.
Conclusions:
- Genetic associations between modifier loci and selected loci, coupled with increasing inbreeding depression, can limit the spread of selfing.
- The stability of outcrossing populations against increased selfing depends on inbreeding depression levels exceeding one-half.
- These findings highlight the complex interplay between selfing rates, heterozygous advantage, and the evolution of mating systems.
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