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Personalised recommendations. Cite protocol How to cite? ENW EndNote. 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.
However, D. Reasons for use in laboratories D. 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 eggs per day, and perhaps 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.
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 Its complete genome was sequenced and first published in Sexual mosaics can be readily produced, providing an additional tool for studying the development and behavior of these flies.
Genetic markers D. 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. 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; 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.
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. 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 study concluded that food supplementation with mM alpha-ketoglutarate decreased Drosophila alcohol sensitivity over time.
For the gene that codes for ADH, there are known classic and insertion alleles. 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.
Drosophila show many of the same ethanol responses as humans do. Low doses of ethanol produce hyperactivity, moderate doses incoordination, and high doses sedation. 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. 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.
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. 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.
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. 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. Triple mutant male fruit fly Drosophila melanogaster exhibiting black body, vestigial wings, and brown eyes mutations. 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.
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 , 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. It was found that the greater the density in eye pigmentation, the greater the success in mating for the males of Drosophila melanogaster. 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.
Wild-Type Wing left vs. Miniature Wing right. Female left and male right D. 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. 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. Extensive images are found at FlyBase. 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. Drosophila flies have both X and Y chromosomes, as well as autosomes.
Unlike humans, the Y chromosome does not confer maleness; rather, it encodes genes necessary for making sperm. Sex is instead determined by the ratio of X chromosomes to autosomes. Simply place the flies back into the culture vial when finished.
There are no long-lasting side effects to this method, although flies left in the refrigerator too long may not recover. Another way to keep flies chilled is adding water to zip-lock type freezer bags, place in the freezer with a petri dish nestled on the bag, and allow to freeze. Transferring flies from one vial to another Flies should be transferred every 10 to 14 days. Students should maintain a backup culture of their flies and the instructor should maintain backup stock cultures of all fly strains.
There are two basic ways to transfer flies when forming new cultures. One requires no anesthetizing but quick hands. A Place a funnel in the mouth of a fresh culture vial that already has media added.
In the old vial the one with flies in it , gently tap the flies down by softly tamping the vial on a soft surface, such as a mouse pad. The flies will fall to the bottom and remain there for a few seconds no more than that!
B An alternative way is to put the flies in the freezer for about 8 minutes. This will cause the flies to fall into a state of stupor. After placing a funnel on the new vial, invert the vial with motionless flies into the funnel. Sexing flies It is quite easy to tell males from females and with a little practice students will become confident of their ability to do so.
Notice that males are generally smaller and have a darker and more rounded abdomen. The coloration of the abdomen is the easiest to recognize. In addition, males have tarsal sex combs on their first pair of legs.
These are black and very distinctive but can only be seen under relatively high magnification. With a little practice, by looking at the abdomen students will become proficient in accurately sexing flies. Sexing flies is critical when making crosses, so be sure student are confident in identifying the difference between the sexes.
In order for students to feel comfortable sexing flies, give or have them obtain 25 or more mixed sex flies and allow them to sort the flies into two piles, male and female. Other students in the group and the instructor should verify the sorting. Each member of the group should be able to sex flies. Pictures of males and females. Note the darker abdomen and more rounded appearance of the male. Females also tend to be larger. Females remain virgins for only hours after eclosure and must be collected within this time frame.
NOTE: Females have the ability to store sperm after a single mating, so if the female for a cross is not a virgin, you will not know the genotype of the male used for your cross. It is strongly suggested that you obtain extra virgins in case a mistake is made in identification or the fly dies before mating and egg lying can occur. In a strong culture, multiple virgin females should be easily obtained. Although females are able to lay eggs as virgins, they will be sterile and no larvae will be produced.
Removal method Remove all flies hours before collecting generally this is done first thing in the morning. Visually inspect surface of food to ensure complete removal of flies. After hours usually before you leave work collect all females that are present. All will be virgins.
Place in a fresh culture vial and wait days look for larvae. Virgin females can lay eggs, but they will be sterile. Since they are photoperiod- sensitive, females tend to eclose early in the morning.
Therefore early collections will ensure the greatest number of virgins for experimentation. However, collection is possible later in the day. Visual method Being able to recognize virgin females removes the necessity of emptying culture vials on a timely basis and allows students to collect their own without the necessity of coming to class at odd times of the day.
Note that virgin females are much larger than older females and do not have the dark coloration of mature females. In addition, in the early hours after eclosure, there will be visible a dark greenish spot the meconium, the remains of their last meal before pupating on the underside of the abdomen. Temperature cycling It is possible to maximize the number of virgins in a morning collection by using temperature cycling. Pictures of virgin males and females:.
A newly eclosed female. The wings and body have a wet appearance. Virgin female showing the meconium arrow. By contrast, males are identified as having one X chromosome and one much smaller Y chromosome. While drosophila only have a total of 4 chromosomes, they too display sexual dimorphism, with females carrying the double X chromosomes and males carrying XY.
The two X chromosomes in female fruit flies, as in mammals, make them a homozygous sex as compared with the XY condition in males, known as heterozygous. One such issue involves an apparent reduction in the number or the level of expression of sex-linked genes on the X chromosome during spermatogenesis.
It is believed that this reduction or silencing of genes on the X chromosome may have profound implications for the evolution of sex chromosomes. During meiotic development of a sperm cell, nature attempts to compensate for the fact that females have two X chromosomes and therefore enjoy a numbers advantage in terms of genes, compared with males. To overcome the bias for female X-linked genes, the X chromosome undergoes inactivation during meiotic sexual differentiation of male gametes, resulting in an underrepresentation of sex-specific genes on the X chromosome.
Some of these genes, which may be beneficial to males, are moved from the X chromosome, to the autosomes, where they may be expressed. The relocation of male-biased genes to the autosomes may be due to a selective advantage favoring genes that move off the X chromosome and therefore avoid X-inactivation during meiosis. Such theories remain controversial however, as statistical analyses are used to evaluate gene frequencies and expression levels, making the proper categorization of genes particularly challenging.
In addition to the steady stream of insights into chromosome evolution, Drosophila are being used as a genetic model for a variety of human diseases including Alzheimer's, neurodegenerative disorders, Parkinson's, Huntington's, as well as extending knowledge of the underlying mechanisms involved in aging, oxidative stress, immunity, diabetes, and cancer.
Materials provided by Arizona State University. Original written by Richard Harth.
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