Drosophila melanogaster

Model organismModel organism in geneticsgenetics Drosophila melanogasterDrosophila melanogaster is a species of fly (the taxonomic order Diptera) in the family DrosophilidaeDrosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Charles W. Woodworth'sCharles W. Woodworth's 19011901 proposal of the use of this species as a model organismmodel organism, D. melanogasterD. melanogaster continues to be widely used for biological research in geneticsgenetics, physiologyphysiology, microbial pathogenesismicrobial pathogenesis, and life history evolution. As of 20172017, five Nobel PrizesNobel Prizes have been awarded to drosophilists for their work using the animal.

D. melanogasterD. melanogaster is typically used in research owing to its rapid life cycle, relatively simple genetics with only four pairs of chromosomes, and large number of offspring per generation. It was originally an African species, with all non-African lineages having a common origin. Its geographic range includes all continents, including islands. D. melanogaster is a common pest in homes, restaurants, and other places where food is served.

Flies belonging to the family TephritidaeTephritidae are also called "fruit flies". This can cause confusion, especially in the MediterraneanMediterranean, AustraliaAustralia, and South AfricaSouth Africa, where the Mediterranean fruit fly Ceratitis capitata is an economic pest.

Wild type fruit flies are yellow-brown, with brick-red eyes and transverse black rings across the abdomenabdomen. The brick-red color of the eyes of the wild type fly are due to two pigments: xanthommatinxanthommatin, which is brown and is derived from tryptophantryptophan, and drosopterins, which are red and are derived from guanosine triphosphateguanosine triphosphate. They exhibit sexual dimorphism; females are about 2.5 mm (0.10 in) long; males are slightly smaller with darker backs. Males are easily distinguished from females based on colour differences, with a distinct black patch at the abdomenabdomen, less noticeable in recently emerged flies, and the sexcombs (a row of dark bristles on the tarsus of the first leg). Furthermore, males have a cluster of spiky hairs (claspers) surrounding the reproducing parts used to attach to the female during mating. Drosophila melanogasterDrosophila melanogaster flies can sense air currents with the hairs on their backs. Their eyes are sensitive to slight differences in light intensity and will instinctively fly away when a shadow or other movement is detected.

D. melanogasterD. melanogaster remains one of the most studied organisms in biological research, particularly in genetics and developmental biology. It is also employed in studies of environmental mutagenesis.

Alfred SturtevantAlfred Sturtevant's Drosophila melanogasterDrosophila melanogaster genetic linkage map: This was the first successful genegene mapping work and provides important evidence for the chromosomechromosome theory of inheritanceinheritance. The map shows the relative positions of allelic characteristics on the second Drosophila chromosome. The distance between the genes (map units) are equal to the percentage of crossing-over events that occurs between different alleles.

D. melanogasterD. melanogaster was among the first organisms used for genetic analysis, and today it is one of the most widely used and genetically best-known of all eukaryotic organisms. All organisms use common genetic systems; therefore, comprehending processes such as transcriptiontranscription and replicationreplication in fruit flies helps in understanding these processes in other eukaryoteseukaryotes, including humanshumans.

Thomas Hunt MorganThomas Hunt Morgan began using fruit flies in experimental studies of heredity at Columbia UniversityColumbia University in 19101910 in a laboratory known as the Fly Room. The Fly Room was cramped with eight desks, each 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. Morgan and his students eventually elucidated many basic principles of heredity, including sex-linked inheritance, epistasis, multiple alleles, and gene mapping.

D. melanogasterD. melanogaster had historically been used in laboratories to study genetics and patterns of inheritance. However, D. melanogasterD. melanogaster also has importance in environmental mutagenesis research, allowing researchers to study the effects of specific environmental mutagens.

D. melanogaster multiple mutantsmutants (clockwise from top): brown eyes and black cuticle (2 mutationsmutations), cinnabar eyes and wildtype cuticle (1 mutation), sepia eyes and ebony cuticle, vermilion eyes and yellow cuticle, white eyes and yellow cuticle, wildtype eyes and yellow cuticle.

There are many reasons the fruit fly is a popular choice as a model organismmodel organism:

• Its morphologymorphology is easy to identify once anesthetized.
• The mature larva has giant chromosomes in the salivary glands called polytene chromosomes, "puffs", which indicate regions of transcription, hence gene activity. The under-replication of rDNADNA occurs resulting in only 20% of DNADNA compared to the brain. Compare to the 47%, less rDNA in SarcophagaSarcophaga barbata ovaries.
• Genetic transformation techniques have been available since 1987 1987.
• Its complete genome was sequenced and first published in 20002000.

Model organism in genetics Drosophila melanogaster is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Charles W. Woodworth's 1901 proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in genetics, physiology, microbial pathogenesis, and life history evolution. As of 2017, five Nobel Prizes have been awarded to drosophilists for their work using the animal.

D. melanogaster is typically used in research owing to its rapid life cycle, relatively simple genetics with only four pairs of chromosomes, and large number of offspring per generation. It was originally an African species, with all non-African lineages having a common origin. Its geographic range includes all continents, including islands. D. melanogaster is a common pest in homes, restaurants, and other places where food is served.

Flies belonging to the family Tephritidae are also called "fruit flies". This can cause confusion, especially in the Mediterranean, Australia, and South Africa, where the Mediterranean fruit fly Ceratitis capitata is an economic pest.

Wild type fruit flies are yellow-brown, with brick-red eyes and transverse black rings across the abdomen. The brick-red color of the eyes of the wild type fly are due to two pigments: xanthommatin, which is brown and is derived from tryptophan, and drosopterins, which are red and are derived from guanosine triphosphate. They exhibit sexual dimorphism; females are about 2.5 mm (0.10 in) long; males are slightly smaller with darker backs. Males are easily distinguished from females based on colour differences, with a distinct black patch at the abdomen, less noticeable in recently emerged flies, and the sexcombs (a row of dark bristles on the tarsus of the first leg). Furthermore, males have a cluster of spiky hairs (claspers) surrounding the reproducing parts used to attach to the female during mating. Drosophila melanogaster flies can sense air currents with the hairs on their backs. Their eyes are sensitive to slight differences in light intensity and will instinctively fly away when a shadow or other movement is detected.

D. melanogaster remains one of the most studied organisms in biological research, particularly in genetics and developmental biology. It is also employed in studies of environmental mutagenesis.

Alfred Sturtevant's Drosophila melanogaster genetic linkage map: This was the first successful gene mapping work and provides important evidence for the chromosome theory of inheritance. The map shows the relative positions of allelic characteristics on the second Drosophila chromosome. The distance between the genes (map units) are equal to the percentage of crossing-over events that occurs between different alleles.

D. melanogaster was among the first organisms used for genetic analysis, and today it is one of the most widely used and genetically best-known of all eukaryotic organisms. All organisms use common genetic systems; therefore, comprehending processes such as transcription and replication in fruit flies helps in understanding these processes in other eukaryotes, including humans.

Thomas Hunt Morgan began using fruit flies in experimental studies of heredity at Columbia University in 1910 in a laboratory known as the Fly Room. The Fly Room was cramped with eight desks, each 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. Morgan and his students eventually elucidated many basic principles of heredity, including sex-linked inheritance, epistasis, multiple alleles, and gene mapping.

D. melanogaster had historically been used in laboratories to study genetics and patterns of inheritance. However, D. melanogaster also has importance in environmental mutagenesis research, allowing researchers to study the effects of specific environmental mutagens.

D. melanogaster multiple mutants (clockwise from top): brown eyes and black cuticle (2 mutations), cinnabar eyes and wildtype cuticle (1 mutation), sepia eyes and ebony cuticle, vermilion eyes and yellow cuticle, white eyes and yellow cuticle, wildtype eyes and yellow cuticle.

There are many reasons the fruit fly is a popular choice as a model organism:

• Its care and culture require little equipment, space, and expense even when using large cultures.
• It can be safely and readily anesthetized (usually with ether, carbon dioxide gas, by cooling, or with products such as FlyNap).
• Its morphology is easy to identify once anesthetized.
• 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 larva has giant chromosomes in the salivary glands called polytene chromosomes, "puffs", which indicate regions of transcription, hence gene activity. The under-replication of rDNA occurs resulting in only 20% of DNA compared to the brain. Compare to the 47%, less rDNA in Sarcophaga barbata ovaries.
• It has only four pairs of chromosomes – three autosomes, and one pair of sex chromosomes.
• 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.
• The development of this organism—from fertilized egg to mature adult—is well understood.
• Genetic transformation techniques have been available since 1987.
• Its complete genome was sequenced and first published in 2000.
• Sexual mosaics can be readily produced, providing an additional tool for studying the development and behavior of these flies.

D. Melanogaster which carries the Cy allele (right), hence showing a characteristic phenotype of curly wings in adult flies. 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 a few common markers below, the allele symbol is followed by the name of the gene affected and a description of its phenotype.

• 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; bristles are shorter and thicker than wild type
• w1: White; eyes lack pigmentation and appear white
• bw: Brown; eye color determined by various pigments combined.
• y1: Yellow; body pigmentation and wings appear yellow, the fly analog of albinism

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. Likewise changes in the Shavenbaby gene cause the loss of dorsal cuticular hairs in Drosophila sechellia larvae. This system of nomenclature results in a wider range of gene names than in other organisms.

• Adh: Alcohol dehydrogenase- Drosophila melanogaster can express the alcohol dehydrogenase (ADH) mutation, thereby preventing the breakdown of toxic levels of alcohols into aldehydes and ketones. While ethanol produced by decaying fruit is a natural food source and location for oviposit for Drosophila at low concentrations (<4%), high concentrations of ethanol can induce oxidative stress and alcohol intoxication. Drosophila's fitness is elevated by consuming the low concentration of ethanol. Initial exposure to ethanol causes hyperactivity, followed by incoordination and sedation. Further research has shown that the antioxidant alpha-ketoglutarate may be beneficial in reducing the oxidative stress produced by alcohol consumption. A 2016 study concluded that food supplementation with 10-mM alpha-ketoglutarate decreased Drosophila alcohol sensitivity over time. For the gene that codes for ADH, there are 194 known classic and insertion alleles. Two alleles that are commonly used for experimentation involving ethanol toxicity and response are ADHs (slow) and ADHF (fast). Numerous experiments have concluded that the two alleles account for the differences in enzymatic activity for each. In comparing Adh-F homozygotes (wild-type) and Adh- nulls (homozygous null), research has shown that Adh- nulls have a lower level of tolerance for ethanol, starting the process of intoxication earlier than its counter partner. Other experiments have also concluded that the Adh allele is haplosufficient. Haplosuffiency states that having one functioning allele will be adequate in producing the needed phenotypes for survival. Meaning that flies that were heterozygous for the Adh allele (one copy of the Adh null allele and one copy of the Adh Wild type allele) gave very similar phenotypical alcohol tolerance as the homozygous dominant flies (two copies of the wild type Adh allele). Regardless of genotype, Drosophila show a negative response to exposure to samples with an ethanol content above 5%, which render any tolerance inadequate, resulting in a lethal dosage and a mortality rate of around 70%. Drosophila show many of the same ethanol responses as humans do. Low doses of ethanol produce hyperactivity, moderate doses incoordination, and high doses sedation.".

• b: black- The black mutation was discovered in 1910 by Thomas Hunt Morgan. The black mutation results in a darker colored body, wings, veins, and segments of the fruit fly's leg. This occurs due to the fly's inability to create beta-alanine, a beta amino acid. The phenotypic expression of this mutation varies based on the genotype of the individual; for example, whether the specimen is homozygotic or heterozygotic results in a darker or less dark appearance. This genetic mutation is x-linked recessive.

• bw: brown- The brown eye mutation results from inability to produce or synthesize pteridine (red) pigments, due to a point mutation on chromosome II. When the mutation is homozygous, the pteridine pigments are unable to be synthesized because in the beginning of the pteridine pathway, a defective enzyme is being coded by homozygous recessive genes. In all, mutations in the pteridine pathway produces a darker eye color, hence the resulting color of the biochemical defect in the pteridine pathway being brown.

• m: miniature- One of the first records of the miniature mutation of wings was also made by Thomas Hunt Morgan in 1911. He described the wings as having a similar shape as the wild-type phenotype. However, their miniature designation refers to the lengths of their wings, which do not stretch beyond their body and, thus, are notably shorter than the wild-type length. He also noted its inheritance is connected to the sex of the fly and could be paired with the inheritance of other sex-determined traits such as white eyes.The wings may also demonstrate other characteristics deviant from the wild-type wing, such as a duller and cloudier color. Miniature wings are 1.5x shorter than wild-type but are believed to have the same number of cells. This is due to the lack of complete flattening by these cells, making the overall structure of the wing seem shorter in comparison. The pathway of wing expansion is regulated by a signal-receptor pathway, where the neurohormone bursicon interacts with its complementary G protein-coupled receptor; this receptor drives one of the G-protein subunits to signal further enzyme activity and results in development in the wing, such as apoptosis and growth.

• se: sepia- The sepia eye color is brown. Ommochromes (brown) and drosopterins (red) are responsible for the typical eye color of Drosophila melanogaster. These mutations occur on the third chromosome. It is due to the inability of the sepia to manufacture a pteridine enzyme that is responsible for the red pigmentation, that they are unable to display the red coloration of the eyes, and instead have the brown coloration as mentioned earlier. When mated with a wild type, flies with red eyes will be dominant over sepia color eyes. They are then classified as a recessive mutation, and can only result when both chromosomes contain the gene for sepia eyes. Sepia colored eyes are not dependent on the sex of the fly. The Sepia eye color decreases sexual activity in males and influences preference of females.

• v: vermilion- Vermilion eye color compared to a wild type D. melanogaster is a radiant red. Vermilion eye color mutant is sex-linked recessive gene due to its absence of brown eye pigment. The red pigment is located on the X chromosome. The synthesis of brown pigment is due to the process of converting tryptophane to kynurenine, vermilion flies lack the ability to convert these amino acids blocking the production of brown pigment. The reduction in the amount of tryptophan converted to kynurenine in vermilion mutants has been associated with longer life spans in comparison to wild-type flies.

• vg: vestigial- A spontaneous mutation, discovered in 1919 by Thomas Morgan and Calvin Bridges. Vestigial wings are those not fully developed and that have lost function. Since the discovery of the vestigial gene in Drosophila melanogaster, there have been many discoveries of the vestigial gene in other vertebrates and their functions within the vertebrates. The vestigial gene is considered to be one of the most important genes for wing formation, but when it becomes over expressed the issue of ectopic wings begin to form. The vestigial gene acts to regulate the expression of the wing imaginal discs in the embryo and acts with other genes to regulate the development of the wings. A mutated vestigial allele removes an essential sequence of the DNA required for correct development of the wings.

• w: white- Drosophila melanogaster wild type typically expresses a brick red eye color. The white eye mutation in fruit flies is caused due to the absence of two pigments associated with red and brown eye colors; peridines (red) and ommochromes (brown). In January 1910, Thomas Hunt Morgan first discovered the white gene and denoted it as w. The discovery of the white-eye mutation by Morgan brought about the beginnings of genetic experimentation and analysis of Drosophila melanogaster. Hunt eventually discovered that the gene followed a similar pattern of inheritance related to the meiotic segregation of the X chromosome. He discovered that the gene was located on the X chromosome with this information. This led to the discovery of sex-linked genes and also to the discovery of other mutations in Drosophila melanogaster. The white-eye mutation leads to several disadvantages in flies, such as a reduced climbing ability, shortened life span, and lowered resistance to stress when compared to wild type flies. Drosophila melanogaster has a series of mating behaviors that enable them to copulate within a given environment and therefore contribute to their fitness. After Morgan's discovery of the white-eye mutation being sex-linked, a study lead by Sturtevant (1915) concluded that white-eyed males were less successful than wild-type males in terms of mating with females. It was found that the greater the density in eye pigmentation, the greater the success in mating for the males of Drosophila melanogaster.

• y: yellow- The yellow gene is a genetic mutation known as Dmel\y within the widely used data base called FlyBase. This mutation can be easily identified by the atypical yellow pigment observed in the cuticle of the adult flies and the mouth pieces of the larva. The y mutation comprises the following phenotypic classes: the mutants that show a complete loss of pigmentation from the cuticle (y-type) and other mutants that show a mosaic pigment pattern with some regions of the cuticle (wild type, y2-type). The role of the yellow gene is diverse and is responsible for changes in behaviour, sex-specific reproductive maturation and, epigenetic reprogramming. The y gene is an ideal gene to study as it is visibly clear when an organisim has this gene, making it easier to understand the passage of DNA to offspring.