Small changes separate man from ape

Tiny genetic changes add up to huge differences when human DNA is compared to that of chimpanzees, researchers have found.

    Scientists say the ape is man's closest relative

    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.

    SOURCE: Reuters


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