Human DNA closer to rats than cats Genome study finds people
are more rodent than carnivore
Rats swarm around a bag of garbage near a Dumpster in New
York. A new study finds human DNA is more closely linked to
rodents than to carnivores.
WASHINGTON - A comparison of human DNA to 12 other animals
shows we share more than our genes and helps show that
people are more closely related to rats than to cats,
scientists reported on Wednesday. The survey also adds to
the argument that so-called "junk" DNA is nothing of the
sort, but must do something important because it stays
virtually identical across many species.
The study also supports what is becoming increasingly clear
- that the strands of DNA we call genes are only a small
part of the genetic story.
The research team at the National Human Genome Research
Institute and several universities compared the same stretch
of DNA in a chimpanzee, baboon, cat, dog, cow, pig, rat,
mouse, chicken, zebrafish and two species of pufferfish -
the Japanese delicacy Fugu and Tetraodon - with human DNA.
In people, this stretch of DNA is a much-studied genetic
region that contains the CFTR gene that, when mutated,
causes cystic fibrosis. "It provides some pretty definitive
evidence that we are indeed closer to rodents than we are to
carnivores," Dr. Eric Green, scientific director of the
NHGRI and leader of the study, said in a telephone
interview.
"Our data really puts the nail in the case. In the sequence
you can find changes in the genome that clearly occurred in
both humans and rodents but did not occur in others."
The changes come in repetitive sequences of DNA that, until
just a few years ago, were believed to be junk - useless
stretches of trash that somehow got saved.
DNA is very difficult to interpret. Its long, long code is
built on just four nucleotides - the compounds known by the
abbreviations A,C,T and G.
A tircky code to break
Reading the long string of four letters repeating in various
combinations is proving to be even trickier than scientists
thought it would be. At first they believed the genes - the
sequences that control production of the protein building
blocks of the body - would be the only functioning parts of
the sequence.
But it turns out there are sequences that control the
genes, and perhaps that do even more. "It now seems that
about 5 percent of our genomes are functionally important,"
Green said.
"Only a third of that codes for genes. That means that two-
thirds of what is functionally important is not (gene)
encoding DNA. We don't even know what it looks like so how
are we going to find it?"
Green hopes to do so by comparing the genomes of different
species. "This is the idea that you can truly use sequences
from multiple genomes and analyze them all at once to try
and find the small percent that is shared among all of
them," he said.
"We believe this is going to be a very valuable way to find
those sequences that are very important."
Why? Because nature cannot ditch vital DNA. "Evolution is
about mixing things up. If evolution has hung on to some
stretch (of DNA), even if it is repetitive, it is telling us
something .. Where did (evolution) find it wasn't safe to
change the genome?" he asked.
Green's team, working with researchers at Pennsylvania State
University, the University of Washington and the University
of California, Santa Cruz, will look at 100 different
regions of the genomes of the 13 species.
This is the first region they have analyzed, they reported
in Thursday's issue of the journal Nature.
"We will discover new types of functional elements in the
coding DNA that we didn't even know existed," Green said.
Copyright 2004 Reuters Limited.
A professor asked a student, "If you had a choice between
the oppressed and the oppressor which would you choose." The
student replied, "Neither". The Professor shook his head and
stated, "You don't have a choice." The student paused and
said, "The oppressed".