Lecture_C.elegans_notes

Lecture_C.elegans_notes - IV. CAENORHABDITIS ELEGANS C....

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1 IV. CAENORHABDITIS ELEGANS C. elegans comprises 959 somatic nuclei, has 302 neurons and 95 body-wall muscles. An unusual feature is that it can be maintained as a hermaphrodite (two X chromosomes): an interesting mutant can be transferred to a fresh plate and, in three days, the self-progeny can be inspected to see if the progeny breeds true. Also males (XO chromosomes) are occasionally generated spontaneously by non-disjunction of X chromosomes during meiosis. The embryo develops through a series of invariant cell divisions that occur during the first 5 h of embryonic development. After about 14 h of development in the egg case, the larva hatches from the eggshell. The animal then passes through four larval stages (L1-L4) that is separated by a period of lethargus , during which the animal sheds its old cuticle. When food is limited, the L1 larvae can enter an alternative developmental programme: the dauer stage in which the animal can survive for months under harsh conditions. The work on C. elegans was pioneered by Sydney Brenner who was looking for a multicellular organism that permits efficient forward genetics. Different criteria for the selection of a genetic modified organism apply to C.elegans: It should be the simplest organism that has the traits of interest Ease of manipulation Small Easy cultivation on Petri dishes or in liquid culture Three-day generation Can be kept as frozen stocks Hermaphrodite In 1974 publication of the first genetic screen, describing ~100 viable mutants with visible phenotype. A. Forward Genetic Screens Different genetic screens can be distinguished: screens to identify mutations in a biological process (ideally uses selection procedures that accelerate identification n of the relevant mutants) simple screens that are routinely used to identify suppressor or enhancer mutations screens of the future: sensitized screens and screens for redundant genes 1. Simple screens: F 2 -screen Is used for visible, recessive mutations. A mutagen (ethyl methane sulphonate –EMS) is used to induce mutations in the sperm and the oocytes of wt hermaphrodites. These worms are grown on Petri dishes for two generations to produce homozygous mutants. Worms with a mutant phenotype are transferred to new plates to determine whether their phenotype is transferred to the next generation (gives about 12,000 copies of a gene can be analyzed in two weeks).
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2 The frequency at which mutations at any particular locus are recovered is about one null mutation for every 2,000 copies of a gene => 6 null mutations can be expected for every gene. The uncoordinated class: This class of animals failed to move normally. UNC-30
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This note was uploaded on 05/28/2010 for the course WE BIBI000000 taught by Professor Johangrooten during the Spring '10 term at Ghent University.

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Lecture_C.elegans_notes - IV. CAENORHABDITIS ELEGANS C....

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