Heterozygote advantage cannot explain MHC diversity, but MHC diversity can explain heterozygote advantage

Area of Science:

• Evolutionary biology
• Immunogenetics
• Population genetics

Background:

• Major Histocompatibility Complex (MHC) genes exhibit remarkable diversity.
• Theoretical studies suggest heterozygote advantage plays a minor role in maintaining this diversity.
• Recent models propose heterozygote advantage alone can explain high MHC diversity.

Purpose of the Study:

• To critically evaluate the role of heterozygote advantage in explaining MHC diversity.
• To demonstrate the limitations of heterozygote advantage as the sole driver of MHC diversity.
• To explore the interplay between MHC diversity and heterozygote advantage.

Main Methods:

• Analysis of theoretical models of heterozygote advantage.
• Examination of parameter sensitivity in existing models.
• Conceptual analysis of selective pressures on MHC haplotypes.

Main Results:

• High MHC diversity generated by heterozygote advantage is highly sensitive to model parameters.
• Heterozygote advantage alone is insufficient to explain widespread MHC gene diversity.
• Selective pressures favoring heterozygotes can lead to increased homozygous fitness, diminishing heterozygote advantage.

Conclusions:

• Heterozygote advantage alone cannot account for the extensive diversity observed in MHC genes.
• The contribution of heterozygote advantage to MHC diversity is likely limited in most species.
• Substantial heterozygote advantage may emerge as a consequence of pre-existing MHC diversity driven by other evolutionary forces.