October 19, 2016
The African clawed frog's
ancestor inherited one set of chromosomes each from two different species and
doubled its whole genome some 18 million years ago, according to an
international research consortium led by Japanese and American scientists who
sequenced the entire genome of the Xenopus laevis for the first time.
Scientists hope that the finding will help our understanding of vertebrate
evolution, as the vertebrate genome doubled twice 500 million years ago.
X. laevis is unusual in that it
is a tetraploid species that has four sets of chromosomes, while
many organisms, including humans, are diploid and have two sets of chromosomes.
How and when this came about has been a topic of debate for some time.
One hypothesis is that the
tetraploid X. laevis inherited one half of its genetic material from each
parent when two diploid ancestral species mated, and the genome of this diploid
offspring then doubled, giving rise to a tetraploid organism with twice the
number of chromosomes as its ancestors.
"X. laevis is an essential
organism for biological and biomedical research, but the
sheer size and complexity of its genome made it difficult for scientists to
sequence the genome in its entirety," says Associate Professor Masanori
Taira, leader of the Japanese research team at the University of Tokyo. He
continues, "He thought that sequencing the entire genome would not only be
valuable for biological and biomedical research but also provide clues as to
the origins of tetraploidy."
The researchers sequenced the entire genome of the J
(Japan) strain of the frog inbred in Japan, in which the genetic codes
inherited from the mother and father, respectively, are identical.
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