From: cbb3-admin@ncbi.nlm.nih.gov on behalf of Joana Silva
[silva@ncbi.nlm.nih.gov]
Sent: Friday, March 22, 2002 6:05 PM
To: cbb3@ncbi.nlm.nih.gov
Subject: CBB seminar - Monday, March 25th

WHERE: Natcher, 6th floor, South conference room

TITLE: Patterns in spontaneous mutations, as revealed by human-baboon 
sequence comparisons.

ABSTRACT: Comparative genomics is a powerful tool with which to study 
the evolutionary process at the molecular level. We aligned a long 
(~1.5Mb) contiguous piece of homologous nuclear DNA obtained from 
moderately divergent species, namely Homo sapiens and Papio 
cynocephalus, the olive baboon. These sequences are ~94% identical, 
which allows for the resolution of the differences between species 
into individual events. Events were divided into substitutions, 
indels and complex events (composed of the previous two). We 
establish that, for substitutions, an individual event consists of a 
single nucleotide substitution while indels and complex events are 
often of length larger than 1. Contrary to what has been proposed, we 
find no evidence that double-nucleotide substitutions are more often 
than expected by chance. In order to determine if there is variation 
in substitution rates along the length of the alignment, we studied 
the distribution of events relative to each other. We found no 
evidence for large scale variation in mutation rate along the 
alignment. However, in a short scale and intermediate scales the 
distribution of mutations along the sequence is over-dispersed, with 
over-dispersion peaking at ~3500 to 5000 nucleotides. This result is 
best explained by varying mutation rates along the sequence rather 
than differences in selective constraint. We conclude that the 
overall mutation process is mostly random, although slight deviations 
from randomness can be detected due to the large amounts of data 
available in this comparison.