Drosophila melanogaster

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Drosophila melanogaster
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Why Study Drosophila?

• Short life cycle
• Small, inexpensive
• Thousands of progeny

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Crossing-Over

• Crossing over only occurs in female Drosophila
• Males maintain linkage relationships of parents
• Limited crossing-over occurs (1-2 per meiosis)
• No crossing-over in heterochromatin or 4th
  chromosome

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Balancer Chromosomes

• These carry multiple, overlapping inversions
• Contain dominant marker and recessive lethal
  mutation
• No recombinant chromosomes are passed on

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P-Element Transposons

• Hybrid Dysgenesis
• Males carrying P elements cross with females
  lacking P elements
• P elements become highly mobile in germ line of
  F1 hybrids
• Chromosome breakage reduces the fertility o
  hybrids
• Progeny of F1 flies carry many new mutations
  induced by P element insertions

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P-Elements

• Transformation
• P-Elements used as vector to introduce cloned DNA
  into organisms
• Tagging
• P-Elements serve as a marker to identify DNA from
  mutant strains
• Enhancer Trapping
• Mobile P-elements act as a reporter to detect
  genes that are turned on in specific tissues

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Genetic Mosaics

• Composed of cells of more than one genotype,
  generated by mitotic recombination
• Allows the study of otherwise lethal alleles to
  be able to produce genes that are heterozygous in
  early development and homozygous in adulthood
  (FLP)

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Ectopic Expression

• Expression at an abnormal time or outside the
  cells or tissues where the gene is normally
  expressed
• Heat-shock control
• Replacing certain enhancer trap vectors with a
  yeast gene that encodes activator proteins
• Introducing synthetic gene into the germ line by
  a P-element

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The Drosophila Genome Project

• 13,600 genes are present
• Gene set appears more similar to that of mammals
  than to that of nematodes
• Only 4,000 genes essential to viability
• Have located many polymorphisms in the genome
  that have speed up the mapping of point mutations
  to the affected gene

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New Direction of Genome Project

• Exploit the many genetic advantages of the fly to
  obtain functional as well as structural
  information about genes
• Isolate as many P-element insertion alleles of as
  many genes as possible
• The development of gene targeting techniques
  should facilitate the systematic inactivation of
  all Drosophila genes
• This means having a nearly complete picture of
  basic gene functions in Drosophila in the future

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