C. elegans

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C. elegans (Caenorhabditis elegans) is a model organism that belongs to the nematode family and are transparent worms that live in neutral soil. This transparency allows for easy observation and manipulation, thus making this a good example of a model organism. They are usually around 1mm in length and are used extensively in research. The Wild - type worms have 959 cells with a fixed a position within the worm, this makes it possible to track individual cells and follow them through development. C. elegans were the first multicellular organism to be sequenced, with their genome being sequenced in 1997. They have a genome of 97 Mbp that encode for 20,000 genes on five pairs of Autosomal chromosomes and two Sex chromosomes.

They are unsegmented creatures that have a bilateral symmetry. They use bacteria growing on decaying substances as a nutrient source.

They have no female sex but are either male or hermaphrodites. This is determined by the number of sex-chromosomes to autosomes. If it is 1:1 then the worm is a hermaphrodite but if it is 1:2 it is male. C. elegans reproduce by laying eggs (laid by the hermaphroditic worms) and can lay up to 1000 eggs, although the average is ~ 300 eggs. However, if a hermaphrodite mates with a male, there can be as many as 1,400 offspring. 1234567

C. elegans have holocentric chromosomes which means that spindle fibres are found attached across the whole length of the chromosome during mitotic division[1].

The great model organism features of C. elegans:

  1. Homologs genes: 1/3 of the genes identified in C. elegans have homologs in the human genome so they are very useful as model organisms when looking at genetic manipulation.
  2. The transparency of C. elegans: Another strong feature that makes the worms so useful for studying is that the adult worms are transparent and have in total 959 cells in the hermaphrodite worms, therefore it is easy to see firstly how the genetic manipulations affect the worms' development and secondly the exact cells in which the genes are expressed. Through studying biological processes occurring in the worms, 3 Nobel Prizes for Medicine have been gained.
  3. Short generation time around 4 days, allowing to see generation effects.
  4. RNAi can be used as a method of knocking down specific genes. C. elegans can be fed with transformed bacteria containing dsRNA of interest.
  5. Embryos are formed as eggs, therefore easily extracted and genetically manipulated to show the effects of knocking out particular genes of interest.
  6. C. elegans are safe to use as they do not naturally cause disease as they are non-pathogenic[2].

References

  1. Hartl, D. L.; Ruvolo, M., 2012. Genetics: Analysis of Genes and Chromosomes. 8 ed. Burlington: Jones and Bartlett Learning, p. 245
  2. http://cbs.umn.edu/cgc/what-c-elegans last accessed: 18/10/16 University of Minnesota Published: 2015
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