Biology · Molecular Basis of Inheritance · NEET
The human genome contains 3164.7 million base pairs (about 3.16 billion bp). This is the exact NCERT number, so remember 3164.7 for NEET. Do not confuse this with the number of genes, which is much smaller (~30,000).
The total number of genes is estimated at about 30,000. This was a big surprise because earlier scientists guessed 80,000 to 1,40,000 genes. NEET often asks you to pick 30,000 as the correct (much lower) estimate.
Chromosome 1 has the most genes (2968). The Y chromosome has the fewest (231). This is a very common NEET fact — Chromosome 1 = most, Y = least.
Less than 2% of the human genome codes for proteins. Most of the genome is made of repeated (repetitive) sequences that do not code for protein directly. So the coding part is very small.
The largest known human gene is dystrophin, with 2.4 million bases. The average gene has about 3000 bases, but sizes vary a lot. Dystrophin is the classic 'largest gene' example for NEET.
Almost all (99.9%) of the nucleotide bases are exactly the same in all humans. That means humans differ in only about 0.1% of bases. This tiny difference is the basis of DNA polymorphism and DNA fingerprinting.
Chromosome 1 was the last of the 24 human chromosomes to be sequenced; its sequence was completed in May 2006. The 24 chromosomes are 22 autosomes plus X and Y. Note: Chromosome 1 is both the last sequenced AND the one with the most genes.
Which chromosome in the human genome has the highest number of genes?
The last chromosome sequenced in Human Genome Project was:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
About 3164.7 million base pairs and roughly 30,000 genes. Remember the base pairs are in millions, but the gene count is only in tens of thousands.
Scientists first guessed 80,000 to 1,40,000 genes, but the Human Genome Project found only about 30,000. One gene can make many proteins through alternative splicing, so fewer genes are needed.
The average human gene has about 3000 bases. But sizes vary greatly, and the largest gene, dystrophin, has 2.4 million bases.
A very large portion. Repetitive sequences are DNA stretches repeated many times (hundreds to thousands). They have no direct coding function but tell us about chromosome structure, dynamics, and evolution.
No. The functions are unknown for over 50% of the discovered genes. So more than half of our genes still need study.
