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Recent origin of HLA-DRB1 alleles and implications for human evolution
T F Bergström1, A Josefsson, H A Erlich
1Department of Genetics and Pathology, University of Uppsala, Biomedical Center, Sweden.
Nature Genetics
|March 21, 1998
Summary
Human leukocyte antigen (HLA) class II DRB1 alleles are younger than previously thought, with most generated after human and chimpanzee divergence. This suggests rapid HLA allele evolution in recent human history.
Area of Science:
- Human genetics
- Evolutionary biology
- Immunogenetics
Background:
- The human leukocyte antigen (HLA) class I and II loci are highly polymorphic.
- Previous studies suggested HLA polymorphism predates human-chimpanzee divergence based on coding sequences.
Purpose of the Study:
- To investigate the evolutionary origin and diversification of HLA class II DRB1 alleles.
- To determine the age of human DRB1 alleles and estimate early hominid population size.
Main Methods:
- Analysis of HLA class II DRB1 intron sequences.
- Comparison of allele divergence times between species.
- Estimation of effective population size (Ne) using coalescence times.
Main Results:
- Intron sequence analysis supports a more recent origin for HLA DRB1 alleles.
- Most human DRB1 alleles (over 90%) generated after Homo and Pan separation.
- Alleles within lineages are approximately 250,000 years old.
- Effective population size for early hominids estimated at ~10^4 individuals.
- Gene conversion and point mutation primarily affect exon 2, not adjacent introns.
Conclusions:
- HLA class II DRB1 polymorphism is largely a post-speciation phenomenon.
- Rapid generation of HLA alleles occurred after human-chimp divergence.
- Localized gene conversion events shape HLA evolution.