Book of Life- human genome

People look very different and behave in wide variety of ways, yet we are told that the genes of any two humans are 99.9% the same.

Logically that should make us a species of clones, so obviously something’s not quite right with the analysis.

Now scientists are discovering that merely comparing individual genes is too simplistic.

A new reading of the "Book of Life", the massive blueprint of human DNA which contains three billion letters of genetic code, has revealed there’s more to the human genome than meets the eye.


By switching attention from the "letters" of the genetic code to "sentences and paragraphs", scientists have made a remarkable discovery.


At least 12% of human DNA varies in the extent to which large chunks of the genetic code are copied or deleted.


Some sequences of the component elements of DNA (the "letters") are repeated many times over, while others are missing altogether in different individuals.


These differences are known as Copy Number Variations (CNVs). And the difference they make is big.


A tenth of human genes, the strands of DNA that provide the coded instructions for making proteins, possess CNVs, researchers have found.


Because having more or fewer copies of a particular gene affects its potency, CNVs are likely to have a powerful impact not only on an individual’s appearance, but also health and disease.


Experts believe the findings, published in the journals Nature and Nature Genetics, could change the face of genetics.


CNVs are already suspected of playing a role in disorders as diverse as Aids, inflammatory bowel disease, lupus, cararacts, damaged arteries, Parkinson’s, Alzheimer’s and schizophrenia.


The international team of scientists analysed DNA from 270 individuals from four populations with ancestry in Europe, Africa or Asia.


They discovered more than 1,400 CNVs, collectively covering about 12% of the genome and six to 19% of any given chromosome, the bundles of DNA that sit in the nuclei of cells. Not only were the changes common, they were also large.


Dr Stephen Scherer, who led a team from The Hospital for Sick Children in Toronto, Canada, said: "We’d find missing pieces of DNA, some a million or so nucleotides long. We used to think that if you had big changes like this, then they must be involved in disease. But we are showing that we can all have these changes."


About 2,900 genes - more than 10% of the human total - had variations in the number of copies of specific DNA segments.


A comparison between two human genome maps, one from the Human Genome Project and the other assembled privately by Celera Genomics Inc, revealed thousands of differences due to CNVs.


The CNV map is expected to transform medical research by helping scientists hunt down the genetic causes of common diseases and inherited disorders.


CNVs may also explain ethnic differences in susceptibility to disease. A striking example is the CCL3L1 gene, which is related to HIV infection, and found in multiple copies in African populations.


Copy number variation is the result of several different mechanisms, some of which are poorly understood. Many studies suggest that larger CNVs occur in regions of the genome that contain or are flanked by duplicated or repeated DNA sequences.


These regions are prone to error when chromosomes are shuffled before being passed from parent to child.