Chromosome 2

Chromosome 2 is one of the twenty-three pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 2 is the second-largest human chromosome, spanning more than 242 million base pairs and representing almost eight percent of the total DNA in human cells.

Chromosome 2 contains the HOXD homeobox gene cluster.

Fusion

Humans have only twenty-three pairs of chromosomes, while all other extant members of Hominidae have twenty-four pairs. Sequencing supports the idea that Neanderthals and Denisovans also had twenty-three pairs.

Human chromosome 2 is a result of an end-to-end fusion of two ancestral chromosomes. The evidence for this includes:

• The correspondence of chromosome 2 to two ape chromosomes. The closest human relative, the chimpanzee, has nearly identical DNA sequences to human chromosome 2, but they are found in two separate chromosomes. The same is true of the more distant gorilla and orangutan.
• The presence of a vestigial centromere. Normally a chromosome has just one centromere, but in chromosome 2 there are remnants of a second centromere in the q21.3–q22.1 region.
• The presence of vestigial telomeres. These are normally found only at the ends of a chromosome, but in chromosome 2 there are additional telomere sequences in the q13 band, far from either end of the chromosome.

The timing of the fusion has been differently estimated by different researchers.

The telomere-to-telomere genome assembly and improved genome assembly techniques have enabled a closer look at the repeat-rich fusion site and the two ancestral centromere sites. The chimp and bonobo chromosome 2A and 2B respectively had an end region similar to chromosome 9 (p end) and chromosome 22 (q end). This likely happened in their common ancestor and was fueled by a pericentromeric inversion in each of their ends (the 2A inversion was only seen in these two species; the 2B inversion also in gorillas). The tips of these two end regions were themselves copies of a common ancestor and they were accidentally misaligned together in a human ancestor and lost. The residual segments similar to 9p24.3 and 22q13.33 around the fusion site support this idea. What appears as the modern vestigial telomere was already vestigial at the time of the fusion, as it was actually from the two ancient inversion events.

Genes

Number of genes

The following are some of the gene count estimates of human chromosome 2. Because researchers use different approaches to genome annotation, their predictions of the number of genes on each chromosome vary. Among various projects, the collaborative consensus coding sequence project (CCDS) takes an extremely conservative strategy. So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes.

List of genes

The following is a partial list of genes on human chromosome 2. For complete list, see the link in the infobox on the right.

p-arm

Partial list of the genes located on p-arm (short arm) of human chromosome 2:

q-arm

Partial list of the genes located on q-arm (long arm) of human chromosome 2:

Related disorders and traits

The following diseases and traits are related to genes located on chromosome 2:

• 2p15-16.1 microdeletion syndrome
• Autism
• Alport syndrome
• Alström syndrome
• Amyotrophic lateral sclerosis
• Brachydactyly type D
• Cleft chin
• Congenital hypothyroidism
• Crigler–Najjar syndrome types I/II
• Dementia with Lewy bodies
• Ehlers–Danlos syndrome
• Ehlers–Danlos syndrome, classical type
• Ehlers–Danlos syndrome, vascular type
• Fibrodysplasia ossificans progressiva
• Gilbert's syndrome
• Harlequin-type ichthyosis
• Hemochromatosis
• Hemochromatosis type 4
• Hereditary nonpolyposis colorectal cancer
• Infantile-onset ascending hereditary spastic paralysis
• Juvenile primary lateral sclerosis
• Lactose intolerance
• Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency
• Lowry-Wood syndrome
• Maturity-onset diabetes of the young type 6
• Mitochondrial trifunctional protein deficiency
• Nonsyndromic deafness
• Photic sneeze reflex
• Primary hyperoxaluria
• Primary pulmonary hypertension
• Sitosterolemia (knockout of either ABCG5 or ABCG8)
• Sensenbrenner syndrome
• Synesthesia
• Waardenburg syndrome
• Hypomyelination with brainstem and spinal cord involvement and leg spasticity

Cytogenetic band

References

External links