Date of Award
6-17-2022
Document Type
Open Access Thesis
Degree Name
Master of Science (MS)
Department
Biology
First Advisor
Chris Maher
Second Advisor
Ken Weber
Third Advisor
Cate Miller
Abstract
The major histocompatibility complex (MHC) is the most polymorphic gene
region in jawed vertebrates. Its gene products play a critical role in determining
individual and population fitness by presenting foreign antigens to immune system
cells, thereby initiating immune response to pathogen and parasite infections and
cancer. I surveyed the literature to investigate how selection maintains such
important adaptive diversity in mammalian populations and how MHC diversity
affects individual and population fitness. Balancing selection in the form of either
heterozygote advantage or rare allele advantage has long been proposed as the key
mechanism for maintaining the extreme diversity in MHC gene alleles. Deviations f
rom Hardy-Weinberg frequencies, excess heterozygosity and high rates of
nonsynonymous base substitutions, as well as
trans-species polymorphisms, point toward past and ongoing balancing selection on
MHC genes. Additionally, mate choice based on MHC genotype is proposed as a
mechanism that contributes to maintenance of the polymorphism. Although most
studies provided some degree of evidence in support of heterozygote advantage,
rare allele advantage, or mate choice in the establishment or maintenance of MHC
polymorphism, the relative importance of the three selective forces reviewed in this
paper remains controversial. My survey suggests that, based on different
demographic and ecological factors, these three nonexclusive mechanisms affect
MHC diversity to varying degrees in different mammalian species.
Recommended Citation
Titterton, Carol MS, "THE ROLEO F SELECTIONIN MAINTAINING MHC VARIATIONI N MAMMALS: HETEROZYGOTAED VANTAGE,R AREA LLELEA DVANTAGEA ND MATE CHOICE" (2022). Student Scholarship. 9.
https://digitalcommons.usm.maine.edu/bio-students/9
Comments
Literature review thesis