December 14, 2004

Chicken genome sequencing, condensed

Here are the main points from the chicken genome sequencing articles below.

  • The chicken is both the first bird to be sequenced and the first agricultural animal to be sequenced.
  • It's a nice middle point between the us mammals (humans, mice, chimps) that have been sequenced, and the much more distantly related plants, fish, and fungus.
  • The chicken genome is much smaller than the mammalian. This is mainly due to reduced duplication and "junk" DNA.

    "The nearly threefold difference in size between the chicken and mammalian genomes reflects a substantial reduction in interspersed repeat content, pseudogenes and segmental duplications within the chicken genome."
    "There is a paucity of retroposed pseudogenes in the chicken genome, in contrast to mammalian genomes, greatly simplifying the classification of chicken gene content."

    I saw someone positing that the relatively small chicken genome was due to the more stringent weight requirements posed for birds by the needs of flight. Given that the sum total weight of all the DNA in a human is so ridiculously small, this theory strikes me as a non-starter.
  • The chicken sequenced was a Burmese Red Jungle Fowl hen. The Jungle Fowl is believed to be the ancestral species from which all domestic chickens derived; thus it was the best representative.

    Why a hen? Well, as any poultry fan knows, hens are the heterogametic sex in chickens. The female chicken has two different sex chromosomes, Z and W. Roosters have two copies of Z. This is the reverse situation from humans, where females are XX, and males are XY.

  • "Rare as hen's teeth" is going to be a valid saying without some serious genetic engineering of the chicken. Chickens are have no genes for the enamel required. You won't be able to milk chickens either -- no genes for casein milk proteins exist.
  • Transposition is evidently uncommon in the chicken. Transposition occurs when sections of the genome "jump" from one position in a chromosome to another, or even to a different chromosome entirely. Chicken genes pretty much seem to stay put. See above comments relating to the efficiency of chicken DNA.

Posted by jeffreyb at December 14, 2004 11:37 PM
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