H
hecd2
Guest
continuation
[Note that other papers agree that substantial variation in DRB1 exon 2 postdates human-chimp divergence (particulatly with regard to rare or private alleles), but that the major haplotypes of exon 2 predate the divergence, concluding that the data is inconsistent with a bottleneck in human ancestry of two individuals. For example Tomas Bergstrom and his team at Uppsala have worked extensively in his field. For example:
Bergstrom et al, Recent Origin of DRB1 alleles and implications for human evolution,* Nature Genetics* 18, 237 (1998), (The human DRB1 alleles can be divided into groups (allelic lineages); most of these lineages have diverged from each other before the separation of Homo and Pan. Alleles within such a lineage, however, appear to be, on average, 250,000 years old, implying that the vast majority (greater than 90%) of the more than 135 contemporary human DRB1 alleles have been generated after the separation of Homo and Pan. The coalescence time of alleles within allelic lineages indicates that the effective population size (Ne) for early hominids (over the last 1 Myr) was approximately 10,000 individuals, similar to estimates based on other nuclear loci and mitochondrial DNA.)
Bergstrom et al, Phylogenetic history of hominoid DRB1 loci and alleles inferred from intron sequences, Immunological reviews 167:351-365 ( …the allelic lineages and alleles of the DRB1 locus were studied based on intron 1 and intron 2 sequences from humans, chimpanzee, bonobo and gorilla. The phylogenetic trees for these sequences indicate that most of the DRB1 allelic lineages predate the separation of the hominoid species studied, consistent with previous analysis of the coding sequences of these lineages.)
van Salome, Gyllensten and Bergstrom, Full length sequence analysis of the HLA-DRB1 locus suggests a recent origin of alleles, Immunogenetics 59, 261 - 267 (2007) (An ancestral “proto HLA-DRB1*03 lineage” appeared to have diverged in the last 5 million years into the human-specific lineages *08, *11, *13, and *14. With exception to exon 2, both the coding- and the noncoding diversity suggests a recent origin (<1 million years ago) for most of the alleles at the HLA-DRB1 locus. Sites encoding for amino acids involved in antigen binding appear to have a more ancient origin.)]
[Also we need to be clear what Shiina et al mean by “narrow bottleneck” when they say “This result finally puts the MHC in line with the bulk of population and evolutionary genetics data, which firmly conclude that a narrow bottleneck has occurred at the origin of our species”. Fortunately they cite two papers in support if this “narrow bottleneck”:
Cann et al, Mitochondrial DNA and Human Evolution, Nature*,* 325 (1987), 31-36 which makes no claims about bottlenecks at all other than to say they might be estimated at some future date
and
Hammer, ’ A recent common ancestry for human Y-chromosomes’, *Nature *378, 376 - 378 which states that their results are compatible with autosomal and mtDNA studies which conclude an effective population size of 10,000 over the last million years citing Takahata, ‘Allelic genealogy and human evolution’, Mol Biol Evol 10, 2 - 22 which supports the figure of 10,000 and states: “The HLA polymorphism thus provides convincing evidence for the absence of severe bottlenecks in almost the entire history of hominoids.”. So when Shiina et al talk about narrow bottlenecks they do not mean two or a few individuals.
All of this is compatible with the consensus findings of studies in multiple loci in the human genome - a very long term mean effective population of 100,000 in human ancestry over 30 million years (comparable with other primates); a mean effective population size of 10,000 in the last million years; and the possibility of one or a few bottlenecks as small as ~1000 individuals lasting for no more than 100 generations. The data is *not *compatible with a severe bottleneck of two or a few individuals in the ancestry of humans.
Alec
evolutionpages.com
[Note that other papers agree that substantial variation in DRB1 exon 2 postdates human-chimp divergence (particulatly with regard to rare or private alleles), but that the major haplotypes of exon 2 predate the divergence, concluding that the data is inconsistent with a bottleneck in human ancestry of two individuals. For example Tomas Bergstrom and his team at Uppsala have worked extensively in his field. For example:
Bergstrom et al, Recent Origin of DRB1 alleles and implications for human evolution,* Nature Genetics* 18, 237 (1998), (The human DRB1 alleles can be divided into groups (allelic lineages); most of these lineages have diverged from each other before the separation of Homo and Pan. Alleles within such a lineage, however, appear to be, on average, 250,000 years old, implying that the vast majority (greater than 90%) of the more than 135 contemporary human DRB1 alleles have been generated after the separation of Homo and Pan. The coalescence time of alleles within allelic lineages indicates that the effective population size (Ne) for early hominids (over the last 1 Myr) was approximately 10,000 individuals, similar to estimates based on other nuclear loci and mitochondrial DNA.)
Bergstrom et al, Phylogenetic history of hominoid DRB1 loci and alleles inferred from intron sequences, Immunological reviews 167:351-365 ( …the allelic lineages and alleles of the DRB1 locus were studied based on intron 1 and intron 2 sequences from humans, chimpanzee, bonobo and gorilla. The phylogenetic trees for these sequences indicate that most of the DRB1 allelic lineages predate the separation of the hominoid species studied, consistent with previous analysis of the coding sequences of these lineages.)
van Salome, Gyllensten and Bergstrom, Full length sequence analysis of the HLA-DRB1 locus suggests a recent origin of alleles, Immunogenetics 59, 261 - 267 (2007) (An ancestral “proto HLA-DRB1*03 lineage” appeared to have diverged in the last 5 million years into the human-specific lineages *08, *11, *13, and *14. With exception to exon 2, both the coding- and the noncoding diversity suggests a recent origin (<1 million years ago) for most of the alleles at the HLA-DRB1 locus. Sites encoding for amino acids involved in antigen binding appear to have a more ancient origin.)]
[Also we need to be clear what Shiina et al mean by “narrow bottleneck” when they say “This result finally puts the MHC in line with the bulk of population and evolutionary genetics data, which firmly conclude that a narrow bottleneck has occurred at the origin of our species”. Fortunately they cite two papers in support if this “narrow bottleneck”:
Cann et al, Mitochondrial DNA and Human Evolution, Nature*,* 325 (1987), 31-36 which makes no claims about bottlenecks at all other than to say they might be estimated at some future date
and
Hammer, ’ A recent common ancestry for human Y-chromosomes’, *Nature *378, 376 - 378 which states that their results are compatible with autosomal and mtDNA studies which conclude an effective population size of 10,000 over the last million years citing Takahata, ‘Allelic genealogy and human evolution’, Mol Biol Evol 10, 2 - 22 which supports the figure of 10,000 and states: “The HLA polymorphism thus provides convincing evidence for the absence of severe bottlenecks in almost the entire history of hominoids.”. So when Shiina et al talk about narrow bottlenecks they do not mean two or a few individuals.
All of this is compatible with the consensus findings of studies in multiple loci in the human genome - a very long term mean effective population of 100,000 in human ancestry over 30 million years (comparable with other primates); a mean effective population size of 10,000 in the last million years; and the possibility of one or a few bottlenecks as small as ~1000 individuals lasting for no more than 100 generations. The data is *not *compatible with a severe bottleneck of two or a few individuals in the ancestry of humans.
Alec
evolutionpages.com