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Related Concept Videos

Multi-species Conserved Sequences02:51

Multi-species Conserved Sequences

Next-generation sequencing technologies have created large genomic databases of a variety of animals and plants. Ever since the human genome project was completed, scientists studied the genome of primates, mammals, and other phylogenetically distant living beings. Such large-scale  studies have provided new insights into the evolutionary relationship between organisms.
Although the genome of each species varies greatly from each other, a few sequences are highly conserved. Such conserved DNA...
Convergent Evolution01:54

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also...
Gene Duplication and Divergence02:37

Gene Duplication and Divergence

The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was  generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.
Exon Recombination02:32

Exon Recombination

The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes. 
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Gene Evolution - Fast or Slow?02:05

Gene Evolution - Fast or Slow?

The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
Synteny and Evolution02:31

Synteny and Evolution

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Around 80 million years ago, the human and mice lineages diverged from the common ancestor. During the course of evolution, the ancestral chromosome underwent...

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Updated: Jun 20, 2026

Stability and Structure of Bat Major Histocompatibility Complex Class I with Heterologous β2-Microglobulin
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Sequence polymorphism and evolution of three cetacean MHC genes.

Shi Xia Xu1, Wen Hua Ren, Shu Zhen Li

  • 1Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210046, China.

Journal of Molecular Evolution
|August 21, 2009
PubMed
Summary

Cetacean major histocompatibility complex (MHC) evolution reveals low variation at DRA but high variability at MHC-I and DQB loci. Extensive allele sharing suggests common ancestry and trans-species evolution, likely driven by balancing selection.

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Area of Science:

  • Immunogenetics
  • Evolutionary Biology
  • Marine Mammal Science

Background:

  • The Major Histocompatibility Complex (MHC) plays a crucial role in immune response and evolution.
  • Understanding cetacean MHC evolution is vital for insights into their immune system adaptation.
  • Previous studies on cetacean MHC genetics are limited, particularly regarding sequence variability and evolutionary patterns.

Purpose of the Study:

  • To investigate sequence variability at three key MHC genes (DQB, DRA, and MHC-I) in cetaceans.
  • To elucidate the evolutionary history and mechanisms shaping MHC diversity in cetaceans.
  • To determine if observed MHC allele sharing reflects common ancestry or convergent evolution.

Main Methods:

  • DNA sequencing of MHC-DQB, DRA, and MHC-I genes from various cetacean species.
  • Phylogenetic reconstruction using molecular clock analysis.
  • Sequence comparison and analysis of allele sharing across species.
  • Comparison of phylogenetic trees based on different genetic sites.

Main Results:

  • Low sequence variation was observed at the DRA locus.
  • Extensive and considerable sequence variability was found at the MHC-I and DQB loci.
  • Significant sharing of identical MHC alleles was detected among different cetacean species.
  • Phylogenetic analyses indicated that allelic similarity likely stems from common ancestry, not adaptive convergence.
  • Evidence for trans-species evolution was found, with MHC diversity predating species divergence.

Conclusions:

  • Cetacean MHC evolution is characterized by differential variability across loci, with MHC-I and DQB showing high diversity.
  • Trans-species evolution and extensive allele sharing are significant features of cetacean MHC.
  • Balancing selection is likely the driving force maintaining high variability and shared alleles at MHC-I and DQB loci in cetaceans.