[talks] KATIE POLLARD talk TODAY in Genomics at 4:15

Mona Singh mona at CS.Princeton.EDU
Mon Sep 24 12:57:27 EDT 2007

Hi everyone,

Katie Pollard from UC Davis Biostatistics  will be speaking in Genomics 
today about what makes us different from chimps ...

See below,

TITLE:  Accelerated and biased nucleotide evolution in the human lineage.

SPEAKER: Katherine Pollard, UC Davis, Dept of Statistics/Genome Center

TIME: 4:15

LOCATION: Carl Ichan Lab 101


Comparative genomics allows us to search the whole human genome for 
examples of lineage-specific evolution. Using a novel likelihood  ratio 
testing approach, we recently identified 202 Human Accelerated  Regions

(HARs) that were extensively changed in the last ~6 million  years since 
divergence from our common ancestor with chimpanzee, but  are highly 
conserved in other species and thus are likely to be  functional. The 
HARs are mostly non-coding sequences, and the set of  genes near HARs is 
enriched for transcription factors, suggesting a  role for HARs in the 
evolution of human gene regulation. We will  describe a few of the most 
intriguing HARs before turning to a  curious observation about the HAR
sequences: the most accelerated  regions show a striking bias for AT to 
GC ("weak-to-strong")  nucleotide substitutions. To investigate whether 
this association  between rate of substitutions and nucleotide bias is a 
genome-wide  phenomenon, we quantified substitution density and bias 
across the  human and chimp genomes. While there is no weak-to-strong 
bias  overall, clusters of nearby substitutions (5 or more within 300bp)
are highly biased. Interestingly, human polymorphisms do not show the
same pattern, suggesting a fixation (rather than mutation) bias. We 
found a strong correlation between nucleotide bias and male 
recombination rates. This observation will be used to speculate about 
the cause of rapid, biased evolution in the primate genome and to  date 
the chromosome fusion that formed human chr2.

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