Drosophila mature through complete metamorphosis, as do all members of the order Diptera.  Diptera are commonly known as (true: having two wings) flies and include many familiar insects such as mosquitoes, black flies, midges, fruit flies, and house flies.  Drosophila melanogaster 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.  Drosophila also have a small number of chromosomes: three autosomal pairs and X/Y 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 pupal stage. This all takes place in roughly six days. Once the Drosophila has entered its pupal stage, it will undergo changes to transform into the adult form and shed its pupal case. The newly emerged adult will be fertile within twelve hours. Of course, temperature does effect the maturation and life cycle of Drosophila. The stated timing of maturation is for a temperature of 25°C; at 18°C development can take twice as long.  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 smaller 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.  According to an experiment in 1911 by Frank Eugene Lutz, the sex combs seem to have very little to do with sexual selection.  Mutations investigated in the class experiment are as follows: apterous , vestigial, bar-eye, and white eye. Crosses were made between virgin wild type males and virgin females that had homozygous mutant alleles for each mutation, separately. These results were presented to the class as the F1 generation. The class experiment began by separating each of the mutations and phenotyping the results. The apterous mutation was easy to analyze, due to the apparent conditions of the mutation. Apterous mutations in Drosophila melanogaster 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 wing of a Drosophila is affected when the vestigial mutation is presented. The wing becomes shriveled or otherwise deformed, and is no longer functional.  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 counterparts. Finally, the bar-eye mutation is one in which the eye appears 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 kidney 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 autosomal chromosomes or sex chromosomes and if it would be dominant or recessive.
Materials and Methods
References: 1. European Bioinformatics Institute © 2006-2008. http://www.ebi.ac.uk/2can/genomes/eukaryotes/Drosophila_melanogaster.html
2. Elland, Carol; NASA Official: Navarro, BJ. Last Updated: September 2006. Accessed November 14, 2008 at http://quest.nasa.gov/projects/flies/lifeCycle.html
3. Definition, found at http://entomology.montana.edu/historybug/glossary.htm#sectD
4. Biology Lab Manual, ed. 8. Vodopich, D., et. Al. Kirkwood Community College – Biology Department BI110/111 Lab. Pages 117-127.
5. Miller, C. 2000. "Drosophila melanogaster" (On-line), Animal Diversity Web. Accessed November 14, 2008 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Drosophila_melanogaster.html.
6. FlyNap Material Safety Data Sheet. http://www.carolina.com/text/teacherresources/MSDS/flynap.pdf
7. Sexual Selection and the Descent of Man: The Darwinian Pivot. By Bernard Grant Campbell. Published by Aldine Transaction, 2006. ISBN 0202308456, 9780202308456. Pages 106-115.
8. Chapter II, The Mechanism of Mendalian Heredity. T. H. Morgan. 1915. http://www.esp.org/books/morgan/mechanism/facsimile/contents/morgan-mechanism-ch02-i.pdf
9. “Apparent Genetic Complexity Generated by Developmental Thresholds: The Apterous Locus in Drosophila Melanogaster”. Mary Stevens.
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