Horizontal gene transfer is the movement of genes from one
living organism to another. There are three types of horizontal gene transfer
(HGT), which are transduction, transformation, and conjugation. Transduction is
the transfer of genes via virus, whereas transformation is when an organism
picks up the genes floating in its environment. Conjugation involves one
organism producing a pilus and injecting the genetic material into another
organism. It is believed that HGT plays an important role in the evolution of
many single celled organisms and in many simpler animals, such as nematode
worms and beetles. However, the notion that HGT takes place in more complex
animals, such as humans, has been debated over the years.
Scientists at the University of Cambridge have conducted a
study about HGT and have ultimately showed that it occurs in animals more than
was previously thought. It was
discovered that HGT has allowed hundreds of active foreign genes to arise in
animals and is believed to have contributed to the evolution of a great deal of
animals, maybe even all of them. With this new information the scientists have
posited that evolution needs to be looked at in a new way.
The study evaluated the genomes of 12 species of the common
fruit fly, 4 species of nematode worms, and 10 species of primates, including
humans. In order to determine how likely it is that the genes were foreign it
was calculated how well the genes matched to similar genes in other species.
Making a comparison to other species allowed the researchers to determine how
long ago the foreign genes were attained. The analysis of these genomes provided more
evidence that the ABO blood group gene and genes
related to metabolism enzymes were acquired by vertebrates through HGT. 17
other genes were also confirmed to have been attained through HGT, while 128 genes not previously noted as foreign were detected. The foreign genes discovered were involved in a
range of activities from lipid metabolism to immune responses. The researchers
also determined that bacteria and protists were the most probable source of the
HGT in all species, though HGT from viruses and fungi was also seen. The HGT from
fungi may be a reason why other studies have negated the idea of HGT in complex
animals as they were only looking for HGT from bacteria.
This study has numerous implications for the future of
genome sequencing. When genomes are sequenced bacterial sequences are often
removed and are thought of as contamination. Although these bacterial sequences
may be due to contamination they may also be part of an organism's genome as
a result of HGT. The researchers warn that screening for contamination still needs
to be in place, but that this new information about HGT should also be considered.
I think that this is such an interesting concept. When I learned
about horizontal gene transfer I had always thought of it occurring between bacteria
or some single celled organism. I had no idea that HGT could occur in multicellular
organisms and never could have imagined that it could happen in humans. I think
that this is positive though as it will contribute to the genetic variation of organisms
and ultimately to evolution.
Link to article: http://www.sciencedaily.com/releases/2015/03/150312123319.htm
Additional link: http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/genetic-exchange/exchange/exchange.html
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