In a report published in the journal Nature on Wednesday Asian scientists explained how
people and apes can be so close, yet so far
apart.
Genetically, chimpanzees are 98.5% identical to
humans. But the differences between the species are clearly
profound and geneticists have been labouring to find out how
such subtle variations in DNA can be so important.
"Clearly, the genomic differences between humans and chimps
are much more complicated than conventional wisdom has
portrayed," Asao Fujiyama of the RIKEN Genomic Sciences Centre
in Japan, and colleagues in Japan, Taiwan and China
wrote.
The comparison will help understand disease and also help
in comparing one person's genetic sequence to another by
helping to set a "base" genetic sequence that can be used to
determine the individual human variations in DNA.
|
"Clearly, the genomic differences between humans and chimps are much more complicated than conventional wisdom has portrayed"
Report published in Nature journal |
Fujiyama's team compared chromosome 22 on three different
chimpanzees to its counterpart in humans, chromosome 21.
Genetic code
They looked for differences that would help separate the
human sequence from the chimp sequence.
Fujiyama's team found just 1.44% of the DNA was
different at the level of single letters of genetic code.
These letters, A, C, T and G, stand for the nucleotides
that make up the DNA of all living creatures. The nucleotides
match up to make amino acids, which in turn string together
into genes that control the proteins made by cells.
There are vast stretches of DNA that do not make up genes
and scientists are struggling to understand their importance.
Fujiyama's team found differences that may be more
important than the single-letter changes.
 |
|
DNA similarities in chimps and
humans can be misleading |
"There is also an impressive number (68,000) of small to
large stretches of DNA that have been either gained or lost
(these are called 'insertions or deletions', 'indels' for
short) in one species or the other," the researchers wrote.
"These differences are sufficient to generate changes in
most of the proteins: indeed, 83% of the 231 coding
sequences, including functionally important genes, show
differences at the amino-acid sequence level."
Brain development
"Our data suggest that indels within coding regions (genes)
represent one of the major mechanisms generating protein
diversity and shaping higher primate species."
In other words, while the genes and other DNA may look the
same in chimpanzees and humans, the proteins they eventually
code for can be very different.
This supports what genetic researchers have been saying
lately - that subtle changes in the genetic code that reach
far beyond the genes themselves may be extremely important to
biology.
|
" These (DNA) differences are sufficient to generate changes in most of the proteins: indeed, 83% of the 231 coding sequences, including functionally important genes, show differences at the amino-acid sequence level"
Report in the journal Nature
|
While there may be no more than about 30,000 to 40,000
human genes, there are more than 250,000 different proteins.
The researchers tried to calculate what the genetic code of
the original ancestor of both looked like, six million to seven
million years ago.
It looked to them as if the original ancestor of human
chimps had a larger genome, and each species pared it down
differently as they evolved.
Some of the genetic differences they found may have direct
implications for disease. They found differences between chimp
and human immune system genes, for instance, and molecules
involved in early brain development.