Salient Features of Human Genome

The human genome is the complete set of genetic material present in a human cell. Before the Human Genome Project, scientists had wildly different guesses about how many genes we had — estimates ranged from 80,000 to 1,40,000. The project's findings replaced those guesses with hard data, and the list below captures the most important facts it revealed.

Size and structure of the genome

The human genome contains 3,164.7 million base pairs (bp). An average gene is about 3,000 bases long, but gene sizes vary enormously. The largest known human gene is dystrophin, which spans 2.4 million bases — that is 800 times the size of an average gene.

Gene count is far lower than expected

The total number of genes is estimated at roughly 30,000. This was a major surprise because earlier predictions had placed the number much higher, between 80,000 and 1,40,000. Despite this relatively small number of genes, almost all (99.9 per cent) of the nucleotide bases are exactly the same in every human. Only 0.1 per cent of the genome accounts for all the genetic differences between individuals.

Most genes have unknown functions

For more than 50 per cent of the discovered genes, scientists still do not know what they do. This is a striking reminder of how much remains to be learned.

Protein-coding DNA is a tiny fraction

Less than 2 per cent of the entire genome actually codes for proteins. The rest — over 98 per cent — was once dismissed as "junk DNA," but we now know it plays critical roles in regulation, structure, and evolution.

Repetitive sequences dominate the genome

Repeated sequences make up a very large portion of the human genome. These are stretches of DNA that are repeated many times, sometimes hundreds or thousands of times. They are thought to have no direct coding function, but they are valuable because they shed light on chromosome structure, dynamics, and evolution.

Gene distribution across chromosomes is uneven

Chromosome 1 has the most genes — 2,968. The Y chromosome has the fewest — just 231. This uneven distribution reflects the different roles and histories of each chromosome.

Single nucleotide polymorphisms (SNPs) are key to human variation …