GENOMICS: The Science born out of the Human Genome Project
· In the human there are large regions of the genome that contains very few genes and others of high gene density. It was believed that human genes were evenly hidden among so much junk DNA in order to protect them. That is, it was more probable that a mutation occurred in the non-coding regions, but due to the non-even distribution of the genes this does not seem to be the case.
· It was a tenant of Molecular Biology the hypothesis of “one gene, one enzyme”. This is also not so, because we make between 300,000 and 500,000 proteins with about 30.000 genes. This means that more than one functional product can be synthesized from a gene sequence depending on how its information is decoded.
· There is also a great deal of duplication in the HG, in the coding as well as in the non-coding regions. It is not known why this happened.
· Today, genetic differences between individuals are expressed in terms of SNPs, Single Nucleotide Polymorphisms. That is, changes of only one base. Those are sites in the genome that have a different base in 1% of the population. More than a million SNPs have been identified and used to construct a map, which is very useful to discover SNPs that are markers for disease-causing genes. By comparing the maps of sick individuals with control groups, or the maps of diseased tissue with normal ones, or of the same tissue before and after a particular treatment, those SNPs present more frequently in one group or tissue than in the other, are markers for the disease. This means that either them or very near them is the mutation responsible for the pathology. Identifying those SNPs is central to the design of tests for early detection of the aberrant gene variant(s) and to find drugs specifically targeted against the molecular cause of the disease.
Why compare the functioning of the HG with that of other animals? Among other reasons, because of the so-called complex diseases, which are caused by the interaction of several genes between them and with the environment. And it is almost impossible to carry out human experiments in which the scientist can change environmental conditions. While this can be readily done with mice or rats.
Since it is easy to breed strains of mice mutants in one or more genes of interest and see how those affect their response to the environmental condition under
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