From Egg to Adult Fly

The egg of the fruit-fly Drosophila melanogaster is long and narrow, with a length of 0.4 mm and a diameter of 0.16 mm. The embryonic development starts immediately after the fertilization and goes on for twenty-four hours, after which the egg hatches and a larva with 14 segments appears. The larval stage consists of three phases, continues for five days and passes into the pupal stage. After some days of pupation and growth, metamorphosis takes place and a new fly emerges, two millimetres long, a fortnight after fertilization.

During the early embryonic development the body becomes divided into 14 invisible segments, and the newly hatched larva contains all of them. Each segment in the larva results in a specific segment in the adult fly. The adult fly consists of a head, three thoracic segments, eight or nine abdominal segments and a tail. The segments differ somewhat but in principle they are organized in the same way. The first thoracic segment develops two legs, the second two legs and pair of wings and the third two legs and a couple of halteres (organs of equilibrium).

Segmentation is not specific to insects. It is a common developmental principle which is also obvious in the early human embryo. Its segment-like somites are the origin of our vertebral column, ribs and certain muscles.

Since the beginning of the 20th century Drosophila melanogaster has been extensively used in genetic research, starting with the American geneticist Thomas Hunt Morgan. In 1933 he was awarded the Nobel Prize in Physiology or Medicine for his discoveries concerning hereditary functions of chromosomes. The Drosophila has only four pairs of chromosomes which facilitates research. Its generation time is short and it is easy to breed.

The development of a

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