Genetics Cross

Topics: Drosophila melanogaster, Gene, DNA Pages: 9 (2548 words) Published: May 1, 2013

The main purpose of this experiment was to find which chromosome our unknown gene mutation is presented on and the exact location on that chromosome. In order to do so many cycles of crosses were completed using linkage analysis on Drosophila melanogaster, a type of fruit fly used in this experiment to identify our unknown gene mutation, unknown. Using virgin bar females crossed with Curly/Plum; Dichaete/Stubble male fruit flies represented our Discriminant Cross one (DC1). The DC1 piloted that the unknown mutation is sex linked dominant. Knowing the mutation is sex linked gives evidence that it is located on chromosome 1. Discriminant Cross two (DC2) is then performed basically to execute a check for DC1 by crossing a wild type female with a Plum/Stubble male fruit fly. In our case if the cross was done correctly all the females should carry the uknown mutation and none of the male progeny should show the unknown phenotype. Following DC2, another cross, called Mapping cross one (MC1), is then executed using a virgin unknown female with males carrying the dominant marker genes for the phenotypes yellow (y), crossveinless (cv), vermillion (v), and forked (f). The final cross that was performed was the Mapping cross two (MC2). The MC2 was carried out by crossing an F1 female from MC1 with an F1 male from MC1. The final step of the procedure is to validate the data obtained in order to confirm our results. This is done using the Chi-square analysis test. In conclusion, by using the data obtained from MC1 and MC2, unknown is approximated to be located at 45.57 m.u. According to the book of mutations in the lab the exact location for unknown is at 57 m.u. Unknown is then found to be bar (b). Introduction

Drosophila melanogaster is most frequently used due to its small size, a conveniently short life cycle of about two weeks, and a small enough genome that helps us understand new mutations compared to our own genome. The goal in performing these many crosses is to figure out the exact map location of the unknown mutation and which chromosome unknown lies on. Over 11,000 species of both wild-type and mutant Drosophila melanogaster exist today that are accessible for research. (Malik, 2010). An example in today’s society shows a study that has been done on a Drosophila melanogaster gene that carries both box and homeobox pairs. The Pax-6 (small eye) gene is a gene located on chromosome IV. It is located close to the locus that carries the eyeless mutation. Ey2 and eyR are two mutations used that widely affect the Drosophila gene expression, especially in the eye primordia. In the finding of the gene ey, human Aniridia, and the Pax-6 mutation in the mouse genome by homologous genes wraps up the conclusion that gene that causes change in the eye is the same for insects and invertebrates (Quiring, 1994). The Drosophila melanogaster has been so frequently used due to the fact that we are acquainted with so many parts of the genome which have already been learned and studied widely. The Drosophila melanogaster is also conveniently a very diminutive size, large amounts are able to be held in a limited amount of space which makes the fruit fly one of the easiest organisms that can be studied to handle. In conclusion, the fruit fly’s genome is most easily studied in a small amount of time. (Manning, 2008).

Materials and methods

Several different materials were used in order to carry out this experiment. A subculture of mutant flies and a subculture of wild-type flies were given to our group. The D. melanogaster were contained in plastic vials carrying their food made from sterilized water added to a dehydrated medium. Each of these plastic vials were then stored at twenty-five degrees Celsius in incubators inside the lab. CO2 was used to ‘knock out’ the flies when the time came to observe and sort the flies. When the flies became immobilized they would be placed onto the viewing plate...
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