Chimp genome reveals answers, more mysteries
July 31, 2005
Special to World Science
Scientists have for the first time published
the draft DNA sequence of the chimp, the closest living relatives to humans.
Comparing the the two species’ genomes could reveal what genetic changes resulted in the evolution of
homo sapiens, researchers say, possibly unlocking some of the oldest mysteries about what it means to be human.
But for now, the data is providing few answers, and some new puzzles.
Sequencing a genome, like piecing together a book in an unfamiliar language, means finding out what all the letters are, and in what order. It doesn’t mean you understand the book. Although biologists have made major strides in deciphering the language of genetic code to gain such an understanding, they’re still a long way from fully doing so.
To start exploring the chimp-human difference through the genome, researchers are examining where the letters are changed between the human and chimp genome. Using that, they can figure out what types of genes these changes affect, if they know where the genes are and what they do.
A preliminary examination of these changes has revealed that, confusingly, most of the changes between humans and chimps seem to affect genes unrelated to language, intelligence or any of the special things we associate with humanity.
Rather, most of the changes are rather in genes that affect our immune and reproductive systems. This actually makes sense, some researchers say, because these are among the fastest-evolving parts of the genome in many animals.
Immune systems evolve rapidly because of evolutionary arms races between animals and the pathogens that attack them. The two sexes also undergo arms races of a sort in sexual organisms, leading to speedy reproductive system evolution.
The genetic changes that
account for what we think of as our “humanness” seem to be fewer and further
between, wrote Wen-Hsiung Li and Matthew A. Saunders of the University of
Chicago in the September issue of the research journal Nature, commenting
on the genome findings.
For instance, as is already
known, just two “letters” of genetic code differ between humans and chimps
in the only gene that has been directly linked to language, a gene called FOXP2.
Cluttering the picture
futher is that most the genetic changes between humans and chimps aren’t
single-letter changes of that type, the pair wrote.
Rather, they are changes
known as insertions, deletions or duplications, which roughly correspond to
duplicated or deleted paragraphs of text in a book. It isn’t clear whether
this type of change or the single-letter change has been more important,
Saunders and Li wrote.
Muddying the picture still
further is that many of the changes of all types could affect genes that don’t
directly influence the functioning of the body. Rather, these genes could simply
serve to influence other genes, such as by activating or deactivating them. It
is still “notoriously difficult” to identify such genes, according to
Saunders and Li.
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