Dear Docs, Medicos and friends of Science and Genetics,

Humans show big DNA differences http://news.bbc.co.uk/1/hi/sci/tech/6174510.stm

DNA comparisons: Gains (green), losses (red), the same (yellow)

Scientists have shown that our genetic code varies between individuals far more
than was previously thought. A UK-led team made a detailed analysis of the DNA
found in 270 people and identified vast stretches in their codes to be
duplicated or even missing. A great many of these variations are in areas of the
genome that would not damage our health, Matthew Hurles and colleagues told the
journal Nature. But others are - and can be shown to play a role in a number of
disorders. To date, the investigation of the human genome has tended to focus on
very small changes in DNA that can have deleterious effects - at the scale of
just one or a few bases, or "letters", in the biochemical code that programs
cellular activity. And for many years, scientists have also been able to look
through microscopes to see very large-scale abnormalities that arise when whole
DNA bundles, or chromosomes, are truncated or duplicated. But it is only
recently that researchers have developed the molecular "tools" to focus on
medium-scale variations of the code - at the scale of thousands of DNA letters.
Big factor


The double-stranded DNA molecule is held together by chemical components called
bases Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
These "letters" form the "code of life"; there are about 2.9 billion base-pairs
in the human genome wound into 24 distinct bundles, or chromosomes Written in
the DNA are about 20-25,000 genes which human cells use as starting templates to
make proteins; these sophisticated molecules build and maintain our bodies

This analysis of so-called copy number variation (CNV) has now revealed some
startling results. It would seem the assumption that the DNA of any two humans
is 99.9% similar in content and identity no longer holds. The researchers were
astonished to locate 1,447 CNVs in nearly 2,900 genes, the starting "templates"
written in the code that are used by cells to make the proteins which drive our
bodies. This is a huge, hitherto unrecognised, level of variation between one
individual and the next. "Each one of us has a unique pattern of gains and
losses of complete sections of DNA," said Matthew Hurles, of the UK's Wellcome
Trust Sanger Institute. "One of the real surprises of these results was just how
much of our DNA varies in copy number. We estimate this to be at least 12% of
the genome. "The copy number variation that researchers had seen before was
simply the tip of the iceberg, while the bulk lay submerged, undetected. We now
appreciate the immense contribution of this phenomenon to genetic differences
between individuals."
Evolving story



A microscope will show up the biggest code abnormalitiesThe new understanding
will change the way in which scientists search for genes involved in disease.
"Many examples of diseases resulting from changes in copy number are emerging,"
commented Charles Lee, one of the project's leaders from Brigham and Women's
Hospital and Harvard Medical School in Boston, US. "A recent review lists 17
conditions of the nervous system alone - including Parkinson's disease and
Alzheimer's disease - that can result from such copy number changes." Scientists
are not sure why the copy variations emerge, but it probably has something to do
with the shuffling of genetic material that occurs in the production of eggs and
sperm; the process is prone to errors. As well as aiding the investigation of
disease and the development of new drugs, the research will also inform the
study of human evolution, which probes genetic variation in modern populations
for what it can say about their relationship to ancestral peoples.

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