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Posts Tagged ‘evolution’

Evolution of the human mind: learning to read the genetic history book

Posted in ASPM, MCPH1, tagged , on November 21, 2007| Leave a Comment »

Human evolution mural at Dover High School
Image by Colin Purrington via Flickr

Comparisons of human genome variation within and across closely related species have great potential to reveal ways in which the brain and mind of modern humans may or may not have differed from our hominid ancestors. Such comparisons have recently revealed a great many genomic targets of natural selection, some of which are expressed in the developing brain, and, hence, might provide clues to the mental life of our ancestors. Variation in two such candidates ASPM (rs964201) and MCPH1 (rs2442496) arose approximately 50,000 years ago and show strong positive selection in the lineage leading to humans. What do these genes and common variants do ? Do they affect language acquisition ? Social behavior ? Intelligence ? Any type of process that might smack of something uniquely ‘human’ ? In their paper [DOI], “Investigation of MCPH1 G37995C and ASPM A44871G polymorphisms and brain size in a healthy cohort“, Dobson-Stone et al., used structural MRI to determine whether differences in whole brain volume or grey matter volume might relate to either or both of these variants. Although no evidence was found that relate these common variants (rare mutations can cause microcephaly) their methodological approach seems like a fantastic strategy for gaining insights into our human origins.

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Talkin’ bout SRPX2

Posted in FOXP2, SRPX2, Sylvian fissure, tagged , , on October 2, 2007| Leave a Comment »

Design and the Elastic Mind - Huma...Image by wallyg via Flickr Can you say this 5 times quickly, “secreted sushi containing SRPX2 as a source of sylvian seizures seems like a spandrel” ? Well, if you can, you might say thanks to your FOXP2 gene (much ado recently), but of course its important to say thanks to so many other co-evolutionary substitutions. A recent article by Royer et al. (doi:10.1186/1471-2156-8-72) examines the recent evolution of the SRPX2 gene and found an R75K change that marks a human-primate split and also occurs in an important functional loop of the first sushi domain of SRPX2 (one that carries a mutation that is responsible for sylvian seizures involving oral and speech dyspraxia). Although they did not find evidence for positive selection, its easy to suspect that Lysine-75 plays an important supporting role in our tongue-twisting skills.

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Genome as an history book: a story of intragenomic coevolution

Posted in MHC loci, tagged , , on July 21, 2007| Leave a Comment »

Schematic representation of MHC class I molecu...
Image via Wikipedia

To me, phylogenetics is one of the coolest ways to use human sequence diversity. I’m not an expert, but roughly speaking, the method involves looking at sequences among ancestral populations and comparisons to sequences in groups that have migrated out over space and time. In these out groups, recombination and mutation have caused genetic sequences to diverge – in some cases new alleles have been naturally selected for, and in most cases, new alleles thrived or crashed due the size and mating structure of a population. The genome carries the historical record of this change – the ultimate history book !

I recently had my Y-chromosome analyzed by the Genographic Project and was intrigued to discover a southwest asian heritage. More recently, Kenneth Kidd and colleagues report a detailed analysis of sequences in the KIR receptor gene complex on chromosome 19q13 and variation in the human leukocyte antigen (HLA) class I gene complex on chromosome 6p23. It has long been known that these regions are hypervariable, which is a good thing since our immune system exploits this diversity to counter ever-changing pathogen invasions – but how do two parts of the immune system continue to work together (KIR receptors bind to HLA antigens) when the separate, unlinked genomic regions show hypervariability ? Worse yet, if the KIR-HLA interaction is too weak, we are susceptible to infection, but, if too strong, we are susceptible to autoimmune attack. Quite a tight-wire to walk, amidst a deluge of pathogen invasions ! Kidd and colleagues use the ALFRED database to reveal some clues to the historical record of this. Apparently, the co-evolution is selective, where activating receptor (19q13) -ligand (6p23) complexes were strongly negatively selected for but not inhibitory receptor-ligand pairs.

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