Drosophila Melanogaster

Introduction

The purpose of the experiment that has been conducted is to breed Drosophila melanogaster for specific traits. We used a dihybrid cross where the traits were sex linked. The cross is considered dihybrid due to the fact that we are crossing two different traits. The traits used for this dihybrid cross experiment are white eyes (w) and vestigial wings (vg). The white eyes are the sex linked trait. These traits were taken and crossed with wild type D. melanogaster.

The experiment that we ran was to be completed by April 20, 2006. There are three other people that I worked with in this experiment, Melissa Broadway, Kelli Hand, and Erin Hill. Kelli and I did a cross that involved wild type/vestigial winged males and white eye/wild type females (fig. 1, 3, 4). Melissa and Erin did the reciprocal cross, which is white eye/wild type males and wild type/vestigial winged females (fig.2, 5, 6). When doing this dihybrid cross, Kelli and my results should have yielded a 3:3:1:1 ratio (wild type, white eye/wild type, wild type/vestigial wing, and white eye/vestigial wing) because our cross was sex linked in favor of the white eyes. Melissa and Erin's results were expected to be a ratio of 9:3:3:1, being wild type, wild type eye/vestigial wing, white eye/wild type wing, and white eye/vestigial wing, respectively.

Drosophila melanogaster are the simple breed of fruit flies that have been selected for the experiment. The life cycle of these organisms is not long, only lasting 50 days from birth. The life cycle from birth to adulthood is only 10-14 days. There are four distinct stages in the life cycle of Drosophila melanogaster. The first is being an egg, and this stage lasts for one day. The second stage is being larva and this lasts for six days. There are three sub-levels of this stage being the first-third instar. The third stage is when the D. melanogaster turns into a pupa, which lasts about 3-4 days. The last stage is the adult (imago) stage of the fruit flies' life, lasting up to thirty-seven days.

This fruit fly's diploid number (2n) is only 8 as opposed to the human number, which is 46. The diploid number is the total number of chromosomes found in every somatic cell or non-sex cell. The haploid number (n) is 4. Humans' haploid number is 23. The haploid number is half the total number of chromosomes and is only found in gametic cells, or sex cells.

There are many characteristics that could have been used for this experiment, including different body color such as ebony and yellow, different wing types other than vestigial such as plexus wings or dumpy wings, and different eye color other than white such as brown eyes or sepia eyes. Eye shape and body shape can also be included in this list of characteristics. The characteristics that have been used in our experiment are wild type characteristics mixed with vestigial wings and white eyes. The vestigial wing characteristic is found on chromosome II located at 67.0. The white eye color characteristic is found on a different chromosome, chromosome I, at 1.5.

These organisms were selected for the experiment for a few reasons. One reason being that they are inexpensive and reproduce quickly, usually within the first eight hours out of becoming a pupa, since their life span is not very long. D. melanogaster also yield results that should easily follow Mendel's four postulates, which can be found on the Furman education website.

Male and female flies are fairly easy to tell apart. The males have round and cylindrical abdomen, while the female fly is generally the larger of the two and her abdomen is distended and pointed. The rear portion of the flies helps in distinguishing between the two as well. The males have fused bands and they are dark. It is clear to see that the females have alternating light and dark bands. A huge factor in distinguishing the sex of the fly is that only the males have sex combs, which are located at about the center on the front two legs of the male.

Materials and Methods

The experiment was held in the genetics lab at the University of Texas at San Antonio which provided the proper tools and allowed the proper amount of area to complete the project. There was plenty of sterile counter space to begin the project. To begin the project our group received two vials, one containing the vestigial winged flies and one containing white eyed flies. An important procedure that was to be followed was to keep the flies in the incubator when we were not observing them. To begin breeding the flies we had to make stock vials of each vial given to us.

Culture preparation is simple. First I poured Ð... a scoop of instant Drosophila medium into a clean vial. Remember that we could not fill the vial more than ј with medium. To make the Drosophila medium soften, I then added an equal amount of mold inhibitor solution to it and mixed gently by swirling. To finish preparing the culture to hold life, I added only two grains of baker's yeast, then placed a foam plug on top of the vial and let it set for about five minutes. The culture is ready to hold flies but I must lay it on its side if I am planning on placing unconscious flies in the vial so they do not get their wings stuck in the culture. If this happens, the flies will die. When they regain consciousness, I was able to turn the culture right side up.

To count the flies, they must be observed under a stereoscope. To be able to observe the flies under the stereoscope, I had to anesthetize them. To do this, I transferred the flies into an anesthetization vial. To transfer the flies to the anesthetization vial, I would gently tap the culture vial on a mouse pad, which should be provided in the lab. This will force the flies to the bottom of the culture vial so you are able to quickly remove the foam plug and place the anesthetization vial on top of the culture vial so the flies are able to make their way to the top of the anesthetization vial. I had to make sure to hold the vials firmly together so flies were not allowed to escape. After most of the flies made their way to the top the anesthetization vial, I would then turn the vials over and tap very carefully as to not dislodge the culture medium, which would smash the flies. I then separated the vials again and plugged the anesthetization vial with a foam plug that had a hole in it, and in the hole I would insert a cotton swab that was soaked in Carolina Fly Nap. The time would be watched very carefully after inserting the Fly Nap because it only takes about 30-45 seconds to put the flies to sleep safely. If the Fly Nap was to be left in the vial for too