Sunday, August 12, 2012

Humans Differ Genetically More Than Previously Thought

We had thought that 99.9% of our genes are the same, but it seems that the figure is nearer 99.5%, say scientists from the Wellcome Trust Sanger Institute, Cambridge, UK and the Hospital for Sick Children, Toronto, Canada. The difference of 0.4% may not seem like much to most lay people, but for scientists it does. Apparently, huge chunks of the human genome may vary from person-to-person.

You can read about this new study in the journal Nature.

The researchers were aiming to discover how chemicals letters are spread across the whole human genome.

We have strands of DNA that span up to hundreds of thousands of chemical letters. The variations are called CNVs (copy number variants). Some of us may have one copy of a DNA segment, while others have two, three, four, and even more. Sometimes the segments are mixed up differently, depending on the person.

Scientists had only been able to look at tiny changes in DNA that could possible harm us - looking at just one, or very few bases (letters) in the code that programs cells. This study looked at things in a much bigger scale.

After examining the genomes of 270 people, the scientists found located 1,447 CNVs in almost 2,900 genes in about 12% of the whole human genome. In other words, it looks like 12% of our genome can have variations within them, depending on the person. The team found long stretches in the people's codes to be duplicated - some were even missing.

We already know that CNVs are associated with a higher risk of developing Alzheimer's disease, Parkinson's disease, HIV and kidney disease. As more CNVs are traced and mapped, scientists will probably link them to other illnesses and conditions. However, of the variations are in parts of the genome that would not damage our health.

Matthew Hurles, Wellcome Trust Sanger Institute, UK, said "Each one of us has a unique pattern of gains and losses of complete sections of DNA. 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."

Scientists do not know why copy variations happen. They suspect it occurs during the production of sperm and eggs (when errors are more likely to take place).

"Global variation in copy number in the human genome"

Click here to view article online

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