What is the human genome?
A human genome consists of all the DNA contained in the nucleus, or core, of a human cell. DNA molecules are very long, so DNA is packaged up tightly into chromosomes. Human cells have 23 pairs of chromosomes – one chromosome of each pair is inherited from each parent. This means that siblings (brothers and sisters) have about half of their DNA in common, while more distant relatives have less DNA in common (first cousins share about one quarter of their DNA).
Humans have two kinds of chromosome: sex chromosomes (the X and Y chromosomes) and autosomes. There are 22 paired autosomes and two sex chromosomes in each cell. Females have two X chromosomes and males have one X chromosome and one Y chromosome.
Each chromosome is made up of a single DNA molecule. DNA contains the instructions for building different parts of a cell and is in the form of a chemical code (the genetic code). DNA is made up of chains of four basic building blocks known as nucleotide bases. These bases are Adenine (A), which is always paired with Thymine (T), and Cytosine (C) which is always paired with Guanine (G).
The human genome is made up of over 3 billion of these genetic bases. Groups of these bases form genes which function to instruct the cell to build other molecules such as proteins. There are between 20,000 and 25,000 genes in the human genome.
What is meant by sequencing the human genome?
Genome sequencing involves working out the order and arrangement of the genetic code. It is technically difficult and expensive. Being able to read this code and understand how the cells translate it into information they can use is fundamental to understanding how our genetic makeup influences our health, development and behaviour.
How much would it cost to sequence my entire genome and can it be done?
The cost of sequencing is dropping dramatically. In 2005, it cost about US$10 million to sequence a human genome. Just two years later, in June 2007, Dr. James Watson, who jointly discovered the structure of DNA in 1953 with the late Dr Francis Crick, received his full genome sequence recorded on a computer hard drive. His genome took less than two months to sequence and cost less than US$ 1 million.
Today, some overseas companies are offering to sequence an individual’s genome for US$20,000. It is relevant to note that a goal of the US National Human Genome Research Institute is to reduce these costs to US$1,000 or less for an entire genome. This is likely to happen within the next few years.