In order to know more about Homo sapiens, we have to understand the sequencing of human genome. A genome is the complete set of genetic instructions encoded in an organism. It is a combination of two words — gene and chromosome. The idea of DNA sequencing was first floated by Nobel laurate Italian-American virologist Renato way back in 1984. The sequencing was initiated in October, 1990. Sequencing simply means determining the order of the base pairs in a segment of DNA.
Molecular units of DNA and RNA are made up of ACGT nucleotides. These combine in various sequences to make the chromosome of any species. Chromosomes are long rod like DNA molecules. DNA, as we are aware, is packed in a double-helix structure consisting of two intertwining spirals. In the DNA ladder, each rung consists of two pairs of nuncleotides, and there are several billion of such pairs in the human genome.
The number of choromosomes differ in different species. Chromosomes form paired sets of 23 or 46 combined together in human beings. One of each pair is donated by one parent. A child thus inherits two copies of every gene. Our immediate predecessors such as apes, gorillas, chimpazees and orangutans have 24 pairs. However, we share 98 per cent of DNA with them.
We have observed already that human genome project (HPG) was initiated in 1990. Its aim is to decode the human genome. Human genome was studied for its order or sequence, gene placement in chromosomes and the linkage maps to track the inherited traits such as eyes, hair colour, disease proneness.
We got the draft genome by 2001. It completed the study of the sequence 90 percent of the total 3 billion base pairs. Still the sequences of 10 per cent of pairs, of say 300 million pairs, is not known. The major portion of this was called junk DNA. Thus we were almost there, but still we had to work to know what the remaining 10 per cent is.
It was in 2003 that a more complete genome was documented. The project which was initiated in 1990 to sequence the entire human genome was complete in 2003. However, it was prematurely announced, since it completed only 92 per cent of base pairs.
DNA gives coded instructions to create proteins which do various things. The DNA that does not give coded instructions is called junk DNA. Why such DNA is there? It too may be performing some functions. By 2022, we have completed 92 per cent of human genome project.
In April 2022, 38 years after the idea of sequencing was first floated, there are research papers that throw light on the last 8 per cent where sequencing was done through Telemere to Telemere (T2T) effort. The project is called T2T-CHM13. Thus it offers a benchmark to compare individuals or entire populations. The T2T determines the sequence, comprising more than 3 billion base pairs across 23 chromosomes. It is gapless.
The two new technologies which facilitated the sequencing emerged in the last decade — the PacBio HiFi DNA sequencing and the Oxford Nanpore DNA sequencing. Both these were used for T2T research.
The work is done but scientists still want decode full sets DNA from a large sample of individuals to factor in all the variations that exist in humans.
Genome research will facilitate in diagnosis and treatment of diseases. There could be preventive medication as we will be alerted about the future risks.
In the US, one research has already mapped genomic changes in 33 cancer types.
In threapeutics, we have already 250 US-FDA approved drugs labelled with pharmacogenomic information. These can be prescribed based on a patient’s genetic information.
In future, medical prescriptions can be based on our genes. There are two aims — to make prescriptions more effective and to reduce the side effects.
The cost of genome sequencing is coming down and is becoming affordable. In India, it costs Rs.10000 to Rs.20000 for genome sequencing.
The sequencing facilities genome editing. Here we can choose the specific embryos to avoid the health problems. It could lead to emergence of superhumans. It is a redline. Here ethics should be the guiding factor.