Question

The last chromosome to be completely sequenced is:

• A. X chromosome
• B. Y chromosome
• C. Chromosome 1
• D. Chromosome 21

Answer 1

The correct option is C Chromosome 1

The Human Genome Project aims at finding out the sequence of the entire genome which involves sequencing of all the chromosomes present in the human genome (22 autosomes, X chromosome and Y chromosome).

It was a mega project which started in 1990 in which several scientists from various countries were involved. The project was completed in 2003. However, the sequence of chromosome 1 was completed only in May 2006 and it remains the last chromosome to be sequenced. It has 2968 genes.

X chromosome is a sex chromosome which is found in both male and female. However, it’s number varies. Females have two X chromosomes. Males have only one of them.
The X chromosome has the largest gene, the dystrophin gene with 2.4 million bp.

Y chromosome is another sex chromosome present only in male. It is also the chromosome with the least number of genes which is 231.

Chromosome 21 is an autosome.
The trisomy of this chromosome causes Down’s Syndrome (the person has three copies of chromosome 21, instead of the usual two copies, in all cells).