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.
Fig. 220.127.116.11 Stages of Drosophila
Some of the reasons for its popularity:
- 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
- They are present during interphase when chromosomes are normally invisible.
- More recently, Drosophila has proven in other ways to have been a happy choice.
- Its embryo grows outside the body and can easily be studied at every stage of development.
- 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).
- Mutations can targeted to specific genes.
Fig. 18.104.22.168 Drosophila chromosomes
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.