Drosophila melanogaster

Within a few years of the rediscovery of Mendel's rules in 1900, Drosophila melanogaster (the so-called fruit fly) became a favorite "model" organism for genetics research.

• The flies are small and easily reared in the laboratory.
• They have a short life cycle The figure shows the various stages of the life cycle (not all drawn to the same scale). A new generation of adult flies can be produced every two weeks.
• They are fecund; a female may lay hundreds of fertilized eggs during her brief life span. The resulting large populations make statistical analysis easy and reliable.
• The giant ("polytene") chromosomes in the salivary (and other) glands of the mature larvae.
  • These chromosomes show far more structural detail than do normal chromosomes, and
  • they are present during interphase when chromosomes are normally invisible.

• Its embryo grows outside the body and can easily be studied at every stage of development.
  For example, it has been possible to count the number of neurons in the brain of a newly-hatched larva. The result: 3,016 neurons of 93 different types. It is estimated that these neurons connect with each other through 548,000 synapses.
• As for the adult brain of this tiny creature, it is made up of 139,255 neurons connecting with each other through 50 million synapses.
• The blastoderm stage of the embryo is a syncytium (thousands of nuclei unconfined by cells) so that, for example, macromolecules like DNA injected into the embryo have easy access to all the nuclei.
• The genome is relatively small for an animal (less than a tenth that of humans and mice). [View]
• Mutations can be targeted to specific genes. [Link to discussion of transposons.]

Chromosomes of Drosophila melanogaster as they appear at metaphase of mitosis. Both sexes have three homologous pairs of autosomes. In addition, the females have two X chromosomes (left), and the males have an X and a Y chromosome (right); these are the sex chromosomes.

• In embryonic development:
  • How a single fertilized egg can give rise to different kinds of cells.
  • How transcription factors guide the organization of the body plan of the embryo.
  • Signals needed to guide the development of the central nervous system.
  • Genetic controls over the building of
    • wings
    • legs
    • eyes
• How the giant chromosomes reveal changing patterns of gene expression.
• Forces at work in evolution
  • sexual selection
  • the benefits of sexual reproduction
• Genetic control of
  • circadian rhythms.
  • foraging behavior