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NCERT Exemplar · Q18

Q.Which was the last human chromosome to be completely sequenced:

(a) Chromosome 1
(b) Chromosome 11
(c) Chromosome 21
(d) Chromosome X
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Chromosome 1 was the last of the 24 human chromosomes to be completely sequenced, finishing in May 2006 — three years after the Human Genome Project's initial "completion" was announced in 2003.

The Human Genome Project (HGP), an international scientific effort launched in 1990, set out to determine the complete sequence of the roughly 3 billion base pairs that make up human DNA. In April 2003, the project announced that sequencing of the human genome was complete. But "complete" here needs a small qualification: the 2003 announcement was a landmark milestone, not literally every single chromosome finished to the last base on that exact date. Sequencing of the most difficult chromosomes continued for a few more years afterward.

Among the 24 human chromosomes (22 autosomes plus the X and Y sex chromosomes), Chromosome 1 is the largest, carrying the most genes of any human chromosome (about 2,968, per the Human Genome Project's own findings). Its sheer size and its share of repetitive sequences made it the most technically demanding to finish closing every gap in.

Important

The sequence of Chromosome 1 was completed only in May 2006 — making it the last of the 24 human chromosomes to be fully sequenced, a full three years after the Human Genome Project's overall 2003 completion announcement. …

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