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Chromosome 2

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Chromosome 2 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 2 is the second largest human chromosome, spanning more than 237 million base pairs [1] (the building material of DNA) and representing almost 8% of the total DNA in cells.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 2 likely contains 1,491 genes, including those of the HOXD homeobox gene cluster.[2]

Evolution

Further information: [[:Genes of the Chromosome 2 fusion site in chimpanzees]]

All members of Hominidae except humans have 24 pairs of chromosomes. Humans have only 23 pairs of chromosomes. Human chromosome 2 is widely accepted to be a result of an end-to-end fusion of two ancestral chromosomes. [3][4]

Fusion of ancestral chromosomes left distinctive remnants of telomeres, and a vestigial centromere

The evidence for this includes:

  • The correspondence of chromosome 2 to two ape chromosomes. The closest human relative, the chimpanzee, has near-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. [5][6]
  • The presence of a vestigial centromere. Normally a chromosome has just one centromere, but in chromosome 2 there are remnants of a second centromere. [7]
  • 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 middle. [8]

Some feel that chromosome 2 presents very strong evidence in favour of the common descent of humans and other apes. According to researcher J. W. IJdo, "We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2." [8] However, because the fusion of two ancestral chromosomes into human chromosome 2 presumably occurred after the human line split from the remainder of the great apes, it cannot provide evidence of common descent[citation needed]. The overall genetic similarity between humans and the remainder of the great apes is the true underlying evidence of common descent in this case--and that overall similarity exists regardless of the fusion event. To understand why the fusion event cannot be used as evidence of common descent, consider the following thought experiment. Imagine that chromosomes 8 and 9 fuse in a modern-day human, resulting in a 22-chromosome-pair individual. This mutation subsequently spreads throughout the global population, eventually replacing all 23-chromosome-pair individuals. This event would not be considered evidence for common descent with great apes. It can only be used as evidence that human chromosomes were different before the fusion event than they are after the fusion event. The same holds for the chromosome 2 fusion event. Only mutations that precede the split between the human line and the remainder of the great apes can be used as evidence of common descent.

Genes

The following genes are located on chromosome 2:

  • ABCA12: ATP-binding cassette, sub-family A (ABC1), member 12
  • ABCG5 and ABCG8: ATP-binding cassette, subfamily A, members 5 and 8
  • AGXT: alanine-glyoxylate aminotransferase (oxalosis I; hyperoxaluria I; glycolicaciduria; serine-pyruvate aminotransferase)
  • ALMS1: Alstrom syndrome 1
  • ALS2: amyotrophic lateral sclerosis 2 (juvenile)
  • BMPR2: bone morphogenetic protein receptor, type II (serine/threonine kinase)
  • COL3A1: collagen, type III, alpha 1 (Ehlers-Danlos syndrome type IV, autosomal dominant)
  • COL4A3: collagen, type IV, alpha 3 (Goodpasture antigen)
  • COL4A4: collagen, type IV, alpha 4
  • COL5A2: collagen, type V, alpha 2
  • HADHA: hydroxyacyl-Coenzyme A dehydrogenase/3-ketoacyl-Coenzyme A thiolase/enoyl-Coenzyme A hydratase (trifunctional protein), alpha subunit
  • HADHB: hydroxyacyl-Coenzyme A dehydrogenase/3-ketoacyl-Coenzyme A thiolase/enoyl-Coenzyme A hydratase (trifunctional protein), beta subunit
  • MSH2: mutS homolog 2, colon cancer, nonpolyposis type 1 (E. coli)
  • MSH6: mutS homolog 6 (E. coli)
  • NR4A2: nuclear receptor subfamily 4, group A, member 2
  • OTOF: otoferlin
  • PAX3: paired box gene 3 (Waardenburg syndrome 1)
  • PAX8: paired box gene 8
  • PELI1: Ubiquitin ligase
  • SLC40A1: solute carrier family 40 (iron-regulated transporter), member 1
  • TPO: thyroid peroxidase
  • TBR1: T-box, brain, 1

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

Intelligence

Recent studies suggest that genes on chromosome 2 may play an important role in human intelligence. [9]

References

  1. ^ Hillier; Graves, TA; Fulton, RS; Fulton, LA; Pepin, KH; Minx, P; Wagner-Mcpherson, C; Layman, D; Wylie, K; et al. (2005). "Generation and annotation of the DNA sequences of human chromosomes 2 and 4". Nature. 434 (7034): 724–31. doi:10.1038/nature03466. PMID 15815621. {{cite journal}}: Explicit use of et al. in: |author= (help)
  2. ^ Vega Homo sapiens Overview of Chromosome 2
  3. ^ Human Chromosome 2 is a fusion of two ancestral chromosomes by Alec MacAndrew; accessed 18 May 2006.
  4. ^ Evidence of Common Ancestry: Human Chromosome 2 (video) 2007
  5. ^ Yunis and Prakash; Prakash, O (1982). "The origin of man: a chromosomal pictorial legacy". Science. 215 (4539): 1525–1530. doi:10.1126/science.7063861. PMID 7063861.
  6. ^ Human and Ape Chromosomes; accessed 8 September 2007.
  7. ^ Avarello; Pedicini, A; Caiulo, A; Zuffardi, O; Fraccaro, M; et al. (1992). "Evidence for an ancestral alphoid domain on the long arm of human chromosome 2". Human Genetics. 89 (2): 247–9. doi:10.1007/BF00217134. PMID 1587535. {{cite journal}}: Explicit use of et al. in: |author= (help)
  8. ^ a b IJdo; Baldini, A; Ward, DC; Reeders, ST; Wells, RA; et al. (1991). "Origin of human chromosome 2: an ancestral telomere-telomere fusion". Proceedings of the National Academy of Sciences. 88 (20): 9051–5. doi:10.1073/pnas.88.20.9051. PMC 52649. PMID 1924367. {{cite journal}}: Explicit use of et al. in: |author= (help)
  9. ^ A Linkage Study of Academic Skills Defined by the Queensland Core Skills Test
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