Evolutionary
biologists at the University of Toronto have found that individuals
with low-quality genes may produce offspring with even more inferior
chromosomes, possibly leading to the extinction of certain species over
generations.
A study published in Proceedings of the National Academy of Sciences
(PNAS) predicts that organisms with such genetic deficiencies could
experience an increased number of mutations in their DNA, relative to
individuals with high-quality genes. The research was done on fruit
flies whose simple system replicates aspects of biology in more complex
systems, so the findings could have implications for humans.
“Mutations
play a key role in cancer and other health problems affecting humans
and other species,” says Nathaniel Sharp, PhD candidate in U of T’s
Department of Ecology & Evolutionary Biology (EEB) and lead author
of the study. “Our research suggests that the problem is likely to
compound over time, leading to a mutational meltdown that may devastate
endangered populations, and increase the risk of health problems in
families in poor condition.”
Sharp
and EEB professor Aneil Agrawal examined the accumulation of mutations
in the fruit fly Drosophila melanogaster, the genes of which are
arranged on three major chromosomes. To manipulate genetic quality, they
introduced harmful mutations onto the fly’s third chromosome. They then
observed how the presence of these mutations affected the fitness of
the second chromosome over 46 generations.
“Copies
of chromosome two maintained in strains with poor-quality copies of
chromosome three declined in fitness two to three times faster than
those with good copies of chromosome three, suggesting that poor genetic
quality elevates the mutation rate,” says Sharp. While the underlying
mechanism remains unknown, it could be tied to how an affected
individual is less capable of repairing DNA or is more susceptible to
DNA damage.
Fruit
flies are especially useful for genetic studies such as this for the
ability to screen for thousands of genes in thousands of flies much
faster than in mammals. Flies are inexpensive to care for and reproduce
rapidly, allowing for several generations to be studied in just a few
months.
The
researchers do, however, offer a more positive possible result of the
process. “An elevated mutation rate under conditions of genetic or
environmental stress could also accelerate adaptation to new
environments,” says Sharp.
The
findings are reported in the paper “Evidence for elevated mutation
rates in low-quality genotypes”. The research is supported by funding
from the Natural Sciences and Engineering Research Council of Canada in
the form of a Discovery Grant to Agrawal and a Vanier Scholarship to
Sharp.
Source: University of Toronto
