Preprint Review Version 1 Preserved in Portico This version is not peer-reviewed

Why do Inbreeding Depression and Load Resist Both Purging and Fixation?

Version 1 : Received: 29 October 2020 / Approved: 30 October 2020 / Online: 30 October 2020 (10:18:40 CET)

How to cite: Waller, D. Why do Inbreeding Depression and Load Resist Both Purging and Fixation?. Preprints 2020, 2020100634 (doi: 10.20944/preprints202010.0634.v1). Waller, D. Why do Inbreeding Depression and Load Resist Both Purging and Fixation?. Preprints 2020, 2020100634 (doi: 10.20944/preprints202010.0634.v1).

Abstract

Upon inbreeding, the architecture of the inbreeding load shifts as selection purges strongly deleterious recessive mutations and drift fixes many milder ones. Most small inbred populations show limited genetic variation while crosses between such populations commonly express pronounced heterosis, confirming fixation. In contrast, purging appears to be limited in that inbred populations often retain substantial inbreeding depression. In addition we have the enigma Darwin noted: purely selfing taxa are unknown. Because both purging and fixation reduce inbreeding depression and load, another mechanism must exist to sustain these. Background selection and the associations that develop among alleles in small inbred populations will shift the architecture of the load potentially creating blocks of recessive mutations linked in repulsion. This would generate pseudo-overdominance that could sustain these “PODs” and inbreeding load. Recombination and crosses between lineages could erode PODs. Crosses between populations fixed for different mutations would generate high pseudo-overdominance, enhancing heterosis and potentially POD formation. New recessive mutations arising within PODs would reinforce overdominance. PODs should generate clear genetic signatures including genomic hotspots of heterozygosity and linkage disequilibrium containing alleles at intermediate frequency generating segregating load. Results from several simulation and empirical studies match these predictions. Further simulations and comparative genomic analyses are needed to rigorously test whether PODs exist in sufficient strength and number to generate persistent inbreeding depression and load in inbred lineages.

Keywords

genetic load; purging; drift load; pseudo-overdominance; heterozygosity-fitness correlation; genomic architecture

Subject

BIOLOGY, Anatomy & Morphology

Comments (2)

Comment 1
Received: 8 December 2020
Commenter: Alain Charcosset
The commenter has declared there is no conflict of interests.
Comment: I have been very interested by ideas related to pseudo-overdominance. Some elements in maize in the reference below if this can be of interest.

The Genetic Basis of Heterosis: Multiparental Quantitative Trait Loci Mapping Reveals Contrasted Levels of Apparent Overdominance Among Traits of Agronomical Interest in Maize (Zea mays L.)‎
By: Lariepe, A.; Mangin, B.; Jasson, S.; et al.
GENETICS Volume: ‏ 190 Issue: ‏ 2 Pages: ‏ 795-U835 Published: ‏ FEB 2012
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Response 1 to Comment 1
Received: 9 December 2020
Commenter:
The commenter has declared there is no conflict of interests.
Comment: Thank you for this suggestion. Yes this article is indeed relevant. In fact, I already refer to this paper on line 592 -- thusly:
"Lariépe et al. (2012) also used mapping to localize QTLs for heterotic effects in maize. Tracking heterozygosity, they found most QTLs for grain yield showed apparent overdominance. These QTLs tended to be located near centromeres where low recombination would conserve repulsion linkage."

However, I failed to include it in the Refs Cited section, an oversight I have now corrected.

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