Chromosome 21 Open Reading Frame 77 (C21orf77)

Chromosome 21 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. The trisomy of the 21st chromosome causes Down Syndrome. Chromosome 21 is the smallest human chromosome, 47 million nucleotides (the building material of DNA) and representing about 1.5 percent of the total DNA in cells.In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced.Identifying genes on each chromosome is an active area of genetic research. However, because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 21 likely contains between 300 and 400 genes