5 Chromosome

5 Chromosome represents almost 6% of DNA in cells. People normally have two copies of this chromosome as all other non-sex chromosomes. Chromosome five spans about 181 million base pairs. Base Pairs are two molecules (nucleotides) on opposite DNA strands that are connected. Adenine (A) forms a base pair with thymine (T), as does guanine (G) with cytosine (C) in DNA. Base pairs is how DNA is measured. There are about 1,268 genes in this chromosome.

Hidden in the chromosome 5 sequence are clues to how humans evolved after branching away from chimpanzees. On average, the chromosome is more than 99 per cent similar between chimpanzees and humans, with the greatest similarity found in genes that cause diseases when mutated.

Despite similarities in the overall sequence, the human and chimpanzee chromosomes compared have some structural differences, including one large section that is flipped backwards in humans compared to chimps. Such an inversion makes it impossible for the two chromosomes to pair up when the cell divides to create sperm and eggs. Over time, that incompatibility could have driven a reproductive wedge between the evolving populations.

Moving evolutionarily further away, about one-third of chromosome 5 is similar to a chicken chromosome that determines the chicken's sex, much like the X and Y chromosomes in humans. This finding backs up previous research suggesting that before mammals and birds split 300 million years ago, the sex chromosomes had not yet evolved. After the split, mammals and birds developed their own methods of creating males and females.

One duplicated region on 5 chromosome could eventually help explain how spinal muscular dystrophy is inherited.

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