The Recipe for People
The idea first arose in the mid-eighties. Imagine what we could do if we knew what it looked like? We could understand where we came from. What makes us tick. What makes us sick. We could revolutionize the field of medicine. Forensic science. Biotechnology. Anthropology.
Therein began the quest to sequence the human genome.
DNA structure hastily drawn while my cells were incubating. Normally DNA is twisted, but I don't have those sketching skills. But you get the idea. Nucleotides bind together, like a zipper, creating a 'base pair' . Since A always binds to T, and C to G, scientists only need to sequence one side of the zipper, since they can infer the other side.
Bear with me for a brief lesson on genetics. All the genes within an organism make up a genome. The human genome contains about 20,000 genes, which is neatly packed into 23 chromosomes, and resides within the nucleus of our cells. Genes are a specific region of DNA that contains the instructions to make a specific protein. There are only 4 subunits of DNA; these subunits, called nucleotides, are often denoted as A, C, G, and T (adenine, cytosine, guanine, and thymine). It's all about the sequence of these nucleotides. The sequence of a gene's DNA determines what protein that gene will make. On average, about 1000 of these nucleotides will produce a single protein, and one gene will produce about 3 proteins. (Variation, obviously).
By figuring out the order of these nucleotides, scientists can understand what genes make what proteins, and ultimately the function of those genes and their proteins. If you were a reductionist, you might say that the human genome is a recipe for people.
The Human Genome Project began in 1990, and the first representative human genome was successfully sequenced 13 years later in 2003. It was the world's largest collaborative scientific endeavour.
Whose genome had the honour of being the first to be sequenced? No one knows. The white blood cells of two men and two women were randomly selected from a pool of 20 male and 20 female volunteers. Thus, the first human genome to be sequenced was actually a composite of four men and women. As it turned out, most of the genome (70%) came from a man from Buffalo, New York, known as 'RP11',
As humans, we share 99.99% of our genomes with each other (unless you are an identical twin, like myself, which means that our genome is 100% identical). The remaining 0.01% of genomic difference accounts for the entire variation that exists within the human species. This means that the human genome project has successfully sequenced a representative human genome. It's available online, and it's free for everyone to access.
In 2001, the cost to sequence the human genome was about $100 million dollars. Eight years ago, it was still a substantial $10 million. Currently, it costs a relatively mere $1000 to sequence a human genome. I always find this graph to be an optimistic reminder of how advances in technology can render a seemingly insurmountable task possible.
The time it takes to sequence the genome has also been drastically reduced. The first round of human genome sequencing took 13 years. New sequencing technology like the MinION (pictured right), can plug into a laptop, and spit out the sequence of a human-sized genome in about 24 hours. Analyzing the data, however, requires about 10 graduate students working day and night for a week.
The MinION doubles as a harmonica! (no it doesn't).
Both the cost and time to sequence the human genome has been greatly reduced. So what? Haven't we already sequenced the human genome? Or at least a representative human genome? Isn't the genome that represents 99.99% of everyone's genome enough?
The human genome includes many different versions of the same genes. These versions of genes (allelles) are represented by different nucleotide sequences in a given gene. Where 70% of the population might have an "A" in the 208th nucleotide of gene X, the remaining 30% of the population might have a "C". Such 'single nucleotide polymorphisms' (SNPs) could account for the fact that I have blue eyes, while my son has brown. Or it might account for the fact that while one patient with Crohn's disease responds well to the drug inflixamab, another does not.
Better predicting what kind of medicine to prescribe to a patient is just one of many benefits of identifying these variations in the human genome. I've heard it touted many times in the seminars I attend as a graduate student: the future of medicine will be personalized to your genome.
I will leave you with a fun fact: we share about 50% of our DNA with bananas. Think about that the next time you make a batch of banana bread. It's practically people!
