Drosophila Melanogaster
occupied by students and their experiments. They started off experiments using milk bottles to rear the fruit flies and handheld lenses for observing their traits. The lenses were later replaced by microscopes which enhanced their observations. The Fly Room was the source of some of the most important research in the history of biology. Morgan and his students eventually elucidated many basic principles of heredity, including sex-linked inheritance, epistasis, multiple alleles, and gene mapping.
“Thomas Hunt Morgan and colleagues extended Mendel’s work by describing X-linked inheritance and by showing that genes located on the same chromosome do not show independent assortment. Studies of X-linked traits helped confirm that genes are found on chromosomes, while studies of linked traits led to the first maps showing the locations of genetic loci on chromosomes” (Freman 214). The first maps of Drosophila chromosomes were completed by Alfred Sturtevant.
Model organism in genetics
D. melanogaster types (clockwise): brown eyes with black body, cinnabar eyes, sepia eyes with ebony body, vermilion eyes, white eyes, and wild-type eyes with yellow body
Drosophila melanogaster is one of the most studied organisms in biological research, particularly in genetics and developmental biology. There are several reasons:
The care and culture requires little equipment and use little space even when using large cultures, and the overall cost is low.
It is small and easy to grow in the laboratory and their morphology is easy to identify once they are anesthetized (usually with ether, carbon dioxide gas, by cooling them, or with products like FlyNap)
It has a short generation time (about 10 days at room temperature) so several generations can be studied within a few weeks.
It has a high fecundity (females lay up to 100 eggs per day, and perhaps 2000 in a lifetime).
Males and females are readily distinguished and virgin females are easily isolated, facilitating genetic crossing.
The mature larvae show giant chromosomes in the salivary glands called polytene chromosomes”puffs” indicate regions of transcription and hence gene activity.
It has only four pairs of chromosomes: three autosomes, and one sex chromosome.
Males do not show meiotic recombination, facilitating genetic studies.
Recessive lethal “balancer chromosomes” carrying visible genetic markers can be used to keep stocks of lethal alleles in a heterozygous state without recombination due to multiple inversions in the balancer.
Genetic transformation techniques have been available since 1987.
Its complete genome was sequenced and first published in 2000.
Genetic markers
Genetic markers are commonly used in Drosophila research, for example within balancer chromosomes or P-element inserts, and most phenotypes are easily identifiable either with the naked eye or under a microscope. In the list of example common markers below, the allele symbol is followed by the name of the gene affected and a description of its phenotype. (Note: Recessive alleles are in lower case, while dominant alleles are capitalised.)
Cy1: curly; The wings curve away from the body, flight may be somewhat impaired.
e1: ebony; Black body and wings (heterozygotes are also visibly darker than wild type).
Sb1: stubble; Hairs are shorter and thicker than wild type.
w1: white; Eyes lack pigmentation and appear white, vision may be somewhat impaired.
y1: yellow; Body pigmentation and wings appear yellow.
Drosophila genes are traditionally named after the phenotype they cause when mutated. For example, the absence of a particular gene in Drosophila will result in a mutant embryo that does not develop a heart. Scientists have thus called this gene tinman, named after the Oz character of the same name. This system of nomenclature results in a wider range of gene names than in other organisms.
Genome
D. melanogaster chromosomes to scale with megabase-pair references oriented as in the National Center for Biotechnology Information database. Centimorgan distances are approximate and estimated from the locations of selected mapped loci.
The genome of D. melanogaster (sequenced in 2000, and curated at the FlyBase database) contains four pairs of chromosomes: an X/Y pair, and three autosomes labeled 2, 3, and 4. The fourth chromosome is so tiny that it is often ignored, aside from its important eyeless gene. The D. melanogaster sequenced genome of 165 million base pairs has been annotated and contains approximately 13,767 protein-coding genes which comprise ~20% of the genome out of a total of an estimated 14,000 genes. More than 60% of the genome appears to be functional non-protein-coding DNA involved in