Drosophila Melanogaster Essay

Length: 1669 words

Drosophila Melanomas Introduction Drosophila mature through complete metamorphosis, as do all members of the order Dippier. [5] Dippier are commonly known as (true: having two wings) flies and Include many familiar Insects such as mosquitoes, black files, midges, fruit flies, and house flies. [31 Drosophila melanomas are most commonly known as fruit flies and are used in many genetic studies for a few simple reasons; they are small and easily handled, they have a short life cycle and they are easy to keep large numbers such as the confined spaces of a laboratory or classroom. 1] Drosophila also have a small umber of chromosomes: three autocross pairs and XII chromosomes. This helps to simplify genetic mapping and study. The egg of a Drosophila is around half of a millimeter long and will take one day from fertilization for the embryo to develop and hatch Into Its larvae form. The larvae go through three stages, or instars, before entering the papal stage. This all takes place In roughly SIX days. Once the Drosophila has entered its papal stage, it will undergo changes to transform into the adult form and shed its papal case.

The newly emerged adult will be fertile within

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twelve hours. Of course, temperature does effect the maturation and life cycle of Drosophila. The stated telling of maturation Is for a temperature of ICC; at ICC development can take twice as long. [2] In Drosophila, reproduction occurs rapidly. A single pair of fertile Drosophila can produce hundreds of offspring in Just a couple of weeks and these offspring, like their parents, will be ready to mate within a week. Drosophila have three main body segments and three pairs of segmented legs.

In Its adult form the Drosophila has a rounded head with large, red, compound eyes and three mailer simple eyes; this is characteristic of wild type males and females. The female is slightly larger than the male. Males can be identified easily because they have a greater concentration of black pigmentation at the posterior end of the abdomen and they have sex combs on their forelegs. [4] According to an experiment In 1911 by Frank Eugene Lutz, the sex combs seem to have very little to do with sexual selection. 7] Mutations investigated in the class experiment are as follows: patterns , vestigial, bar-eye, and white eye. Crosses were made between virgin wild type males ND vulgar females that had homozygous mutant alleles for each mutation, separately. These results were presented to the class as the Fl generation. The class experiment began by separating each of the mutations and phenotype the results. The patterns mutation was easy to analyze, due to the apparent conditions of the mutation. Patterns mutations In Drosophila melanomas give rise to aberrant, or missing, wings.

Another mutation affecting wing formation was the vestigial mutation. By definition, vestigial describes a loss of function. This is precisely how the inning of a Drosophila is affected when the vestigial mutation is presented. The wing becomes shriveled or otherwise deformed, and Is no longer functional. [9] The white- eye mutation Is also very easy to Identify. As the name of the mutation Itself states, these flies have white eyes, and are easily distinguished from their red-eyed 1 OFF misshapen. This characteristic can be difficult to distinguish from the wild type.

In some cases, the red portion of the eye will appear as a narrow slit, or red “bar”, thus lending to the name of the mutation itself. In other cases, the eye will appear to be dined shaped instead of ovular; this can be much more difficult to distinguish from the wild type. The experiment was designed to determine the mode of inheritance for each trait; this is to say whether the trait would be associated with autocross chromosomes or sex chromosomes and if it would be dominant or recessive. Materials and Methods To complete the experiment a population of virgin males and virgin females of each mutation to be tested was obtained.

Each mutation being tested would have its own culture tube with a food source at the bottom. The food source can be any umber of things, but for this experiment an instant Drosophila medium was mixed water and a small amount of dry yeast was added. After reproducing, the yeast would serve as a food source. The food source should take up no more than one inch at the bottom of the culture tube. A separate culture tube should be used as a sleep chamber to anesthetize Drosophila before characterizing the phenotypes. 4] For each mutation investigated, a culture tube was prepared by the instructor and the flies in these containers served as the Fl generation, the result of parental crossing of wild type males and mutant females. The first step was to anesthetize the Drosophila so they could be counted and sorted by phenotype. Drosophila can easily be anesthetized and manipulated with unsophisticated equipment. In the case of this particular experiment the substance provided to anesthetize the Drosophila with was called Flyway. Flyway consists of a mixture of: 50% Trampoline, 25% Ethanol, and 25% Fragrances. 6] The flies were transferred from the food chamber to the sleep chamber. Once in the sleep chamber, a foam stopper was placed in the tube and a swab dipped in Flyway was inserted into the container. After roughly 60-90 seconds, the flies were fully anesthetized. Once anesthetized, the flies were carefully poured onto a white index card and divided into four categories: male (0*) wild type, male (0*) mutant, female (4) wild type, and female (4) mutant. A soft, fine- tipped paint brush was used to separate the flies into the appropriate categories to avoid any damage to the specimen.

As stated previously, males can be distinguished from females because of a few different characteristics: females are slightly larger than males, having seven bands on the posterior end of their abdomens and males eave a dark pigment concentration on their posterior end; males can also be identified by sex-combs on their forelegs. After separating, five males and ten females were placed into new culture tubes, containing a food source. The selection of males and females, as instructed, included both wild type and mutants (if any were present).

This was repeated for each mutation and the tubes were labeled and stored for two weeks. At the end of the two week period, it was discovered that the IF generation had not emerged from the papal casing, probably due to a low room temperature. A count of flies present in each culture tube was obtained by repeating the aforementioned method of anesthesia and it was concluded that the adult Drosophila present were from the parent [Fl] generation. At this point, the rhea adults had emerged at the end of the final week and were anesthetized, separated, and counted- all through the same procedure as the Fl generation.

Results Phenotypes found in theoretical crosses, made between wild type male and homozygous mutant female, for mode of inheritance are as follows: Autocross recessive traits are presented as 100% wild type in the Fl generation and as 75% wild hype and 25% mutant characteristics in the IF generation. Autocross dominant traits appear as 100% mutant characteristics in the Fl generation and as 25% wild type and 75% mutant characteristics in the IF generation. Sex-linked traits are divided between males and females.

For sex-linked recessive traits, 100% of females show Mild-type characteristics and 100% of males show mutant characteristics in the Fl generation. In the IF generation, 50% of females appear to be wild type and the other are mutants. Males in the IF generation have the same break down. Sex-linked nominate traits are different from their recessive counterparts. In the Fl generation 100% of both sexes show mutant characteristics. 100% of females in the IF generation display mutant characteristics, while 50% of males show wild type and the other 50% show mutant characteristics. Pick] Conclusion The completed experiment leads me to conclude that the patterns and vestigial mutations are autocross recessive traits, the bar-eye mutation is a sex-linked dominant trait, and the white eye mutation is a sex linked recessive trait. After comparing the theoretical cross for autocross recessive traits to the actual results of he crosses for the patterns mutation and the vestigial mutation, it is easy to see a correlation. As expected of a recessive trait, the Fl generation did not show a significant number of mutations, because recessive traits are masked by dominant traits.

Though not exact, the phenotype percentages produced from each experimental cross were similar to those produced in the theoretical cross for autocross recessive traits.. There seemed to be a few complications that skewed the results for both the bar-eye and the white eye mutations. From personal experience with difficulty, I believe this could be due to a number of factors. First, consider the bar-eye mutation; the bar-eye mutation presents itself in two ways, as a narrow red slit in the eye when its presence is homozygous and as a red kidney shape when heterozygous for the gene.

This is to say that males will always be either Mild type or have the extreme version of the bar-eye mutation: the narrow, red slit. Females, on the other hand can present any of three characteristics associated with this mutation. They may appear as wild type or with the extreme version of the mutation Just as the males, but they may also appear to have kidney-shaped eyes. [8] This is, I believe, one main reason the bar-eye results did not line up with any of the theoretical crosses. Another reason for discrepancy may apply to both the bar-eye mutation and the white eye mutation.

Being that these are both sex-linked traits, it is our class has had little experience working with Drosophila, it is safe to assume that mistakes were made. Even though the comparison between theoretical results and actual experimental results do not line up for either the bar-eye or white eye mutation I have deduced them to be sex linked because of the way they are presented differently in males and females. The bar-eye mutation was key in making this conclusion, since the differences between the sexes is obvious.

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