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Microevolution
Name: Dece M.
Status: Student
Age: 18
Location: N/A
Country: N/A
Date: 2001
Question:
Hi, im researching micorevolution, and was wondering if
you could give me some specific examples of populations in which gene
flow, non-random mating, and genetic drift have resulted in microevolution.
and secondly, how has microevolution come about and what are the
consequences for alleles and genotype frequencies?
Replies:
Hi Dece,
You did not indicate whether you are interested in
higher organisms or not. May I point out
microorganisms as a model to study microevolution.
Bacteria can exchange DNA (by natural transformation,
conjugation or by transfecting phages), their genes
mutate by random drift, and sometimes recombinations
occur within their genome. Since they have such a
short generation time, the effect of these genetic
changes can be detected rapidly, and studied in real
time. One bacterial species that comes to mind is
Helicobacter pylori, which lives in the stomach of
humans and which displays a wide variation in
genotypes between strains. In fact, if you zoom in at
the polymorphisms within genes, one could state that
every individual has his 'own' adapted strain of H.
pylori, but that would still be highly related to the
strain of another individual who was infected by a
common source.
The relative importance of genetic exchange
(horizontal gene transfer) versus mutation (genetic
drift) is a current subject of research. Not all
bacterial species have the ability to spontaneously
take up DNA, but H. pylori does, and it seems that
gene transfer significantly contributes to
micro-evolution.
The mechanism of these events is studied in the
laboratory: how do the bacteria protect themselves
against incoming DNA that would be harmful; how is the
DNA taken up; do mutations (genetic drift) follow a
pattern, these are some of the questions addressed
with H. pylori as a model.
One also has to think what the effect of mutations
will be. It is most likely that any mutation with a
phenotypic effect (that is, a genetic change that has
'some' effect on the properties of the bacteria;
mutations that do not change the amino-acid of
proteins are considered to be 'silent' mutations) will
be selected for the best fit. In other words,
mutations occur all the time but there is selection
for those forms that will be adequately fit for the
niche they occupy. And when the selection pressure
changes (in pathogenic bacteria this can be the onset
of an immune response; or in H. pylori the passage
from one host to another) the best-fit organisms will
survive and multiply.
Microevolution is a fascinating but complex system to
study. If you browse PubMed for 'microevolution and
bacteria' you will find many interesting papers. Two
recent reviews (Ziebuhr et al, Cell. Mol. Life Sci.
1999 Nov 30;56(9-10):719-28. and Schloter et al, FEMS
Microbiol Rev. 2000 Dec;24(5):647-60) are a good
starting point to explore the subject.
Dr. Trudy Wassenaar
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Update: June 2012
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