What Exactly is the Human Genome?

Every organism, including humans, has a genome that contains all of the biological data required to build and maintain that organism. Inside a cell is a nucleus and inside each nucleus are forty-six bundles of chromosomes, twenty-three of which are from the mother of the organism and twenty-three of which are from the father of the organism. Almost every cell in the body carries the same complement of chromosomes with the exception of red blood cells, some immune system cells and egg and sperm cells. Chromosomes constitute the complete set of instructions necessary to make and maintain the body, they are constructed of long strands of the chemical deoxyribonucleic acid or DNA. DNA’s job is to replicate itself and it does it’s job very well, there is heaps of it inside your body, almost two metres of it in almost every cell! Each strand of DNA comprises some 3.2 billion letters of coding! One calculation estimates that there is as much as twenty million kilometres of DNA inside of you! Remarkably, DNA makes proteins but the proteins are made outside the nucleus, away from the actual DNA, this is made possible by RNA, ribonucleic acid which acts as an interpreter between the two. It is one of life’s great anomalies that DNA and proteins don’t speak the same language. For over four billion years they have sustained life yet they have never being able to speak directly and have always required a mediator, RNA translates information from a cell’s DNA into terms proteins can understand. Francis Crick put it thus - DNA makes RNA, RNA makes protein and proteins make us.

A gene is a short piece of DNA which instructs the body on how to build a specific protein, when you put all these genes together you get the human genome. The genome is a type of instruction manual for the body, the chromosomes can be viewed as chapters of the manual and genes as individual instructions for making proteins, the words are called codons and the letters are known as bases. As stated earlier, DNA is great at its job, it replicates itself at a mind-boggling rate and covers an unimaginable workload, however, now and again the poor chap gets a little tired and about one time in a million, a letter gets in the wrong place. When this occurs it is known as a single nucleotide polymorphism, or SNP, fondly referred to by biochemists as Snips. Most of the time these Snips are buried in stretches of non-coding DNA and have no noticeable consequence for the body. However, now and again they do make a difference, sometimes for good sometimes for not so good. For example, it may make the body increase its production of red blood cells which may help the body to live at high altitudes or it may make the body more susceptible to a particular disease. Over time, these modifications accumulate in populations contributing to distinctiveness. These Snips account for the differences between us, otherwise we would all be the same, all indistinguishable from one another, which you must admit would be a truly horrifying prospect!

Our DNA is 99.9 per cent the same, the Snip creates that 0.01 percent difference, luckily creating the beauty that there is a separate human genome for every one of us on the planet. It was believed for quite some time that the human body had over one hundred thousand genes but the results of the Human Genome Project reckoned the figure was more realistically less than thirty thousand. However, it is not the number of that genes that an organism that contains that matters, it is rather the way that the genes co-operate. It would be a whole lot simpler if it was simply the case that individual genes were responsible of specific traits and conditions as you could isolate and modify them. There are a few disorders such as haemophilia, Parkinson’s disease, Huntingdon’s disease and cystic fibrosis are caused by lone dysfunctional genes but normally disruptive genes are weeded out by natural selection. But for the most part, all that we are made up of, whether for good or for bad is created by the co-operation of genes. The Human Genome Project (HGP) was completed in 2003 after thirteen years and the final papers were published in 2006. The project was co-ordinated by the US Department of Energy, the National Institutes of Health (US), the Wellcome Trust (UK). The goals of the project was to identify all the genes in the human body and determine the sequences of over three billion of the chemical base pairs that make up DNA.