A Study Of Inheritable Traits in Fruit Flies
The Drosophila melanogaster, more commonly known as the fruit fly, is a popular species used in genetic experiments. In fact, Thomas Hunt Morgan began using Drosophila in the early 1900's to study genes and their relation to certain chromosomes(Biology 263). Scientists have located over 500 genes on the four chromosomes in the fly. There are many advantages in using Drosophila for these types of studies. Drosophila melanogaster can lay hundreds of eggs after just one mating, and have a generation time of two weeks at 21°C(Genetics: Drosophila Crosses 9). Another reason for using fruit flies is that they mature rather quickly and don't require very much space. Drosophila melanogaster has a life cycle of four specific stages. The first stage is the egg, which is about . 5mm long. In the 24 hours when the fly is in the egg stage, numerous cleavage nuclei form. Next, the egg hatches to reveal the larva. During this stage, growth and molting occur. Once growth is complete, the Drosophila enter the pupal stage, where it develops into an adult through metamorphosis. Upon reaching adulthood, the flies are ready to mate and produce the next generation of Drosophila melanogaster.
During this experiment, monohybrid and dihybrid crosses were conducted with Drosophila melanogaster. Our objective was to examine the inheritance from one generation to the next. We collected the data from the crosses and analyzed them in relation to the expected results.
MATERIALS AND METHODS
For the monohybrid cross in this experiment, we used an F1 generation, which resulted from the mating of a male homozygous wild-type eyed fly with a female homozygous sepia eyed fly. Males and females are distinguished by differences in body shape and size. Males have a darker and rounder abdomen in comparison to females, which are more pointed. Another difference occurs on the forelegs of the fliesmales have a small bump called sex combs. At week 0, after being anaesthitized by fly-nap, three males and three females were identified under a dissecting microscope and placed in a plastic vial with a foam stopper at the end. The vial remained on it's side until the flies regained consciousness so that they didn't get trapped by the culture medium at the bottom. We allowed the Drosophila to incubate and reproduce for a week. After one week, the vial contains many larva in addition to the F1 generation flies. Next, we removed the F1 generation flies to prevent breeding between the two generations. Acting as Dr. Kevorkian, we gave the F1 generation a lethal dose of the seemingly harmless anesthesia, fly-nap. A trumpet solo of "Taps" played in our minds as we said goodbye and placed them in the fly morgue. We allowed the F2 larval generation to incubate for two weeks. The experiment called for one week of incubation, but Easter fell during that week which interfered with our lab time. After the two weeks, the F2 flies were also terminally anaesthetized. Only, before saying goodbye, we separated the flies according to sex and eye color(wild-type,red or mutant, sepia), recording the results in Table 1. The same method was used it the dihybrid cross, except, instead of one trait, two traits were observed. The traits were eye-color(wild-type, red or mutant, sepia) and wing formation(wild-type, full or mutant, vestigial). The F1 generation for the dihybrid cross came from a cross between a male homozygous wild-type for eyes and wings, and a female homozygous for sepia eyes and vestigial wings. The results of this cross were recorded and appear in Table 2.
The monohybrid cross of Drosophila melanogaster produced 25,893 flies for all of the sections combined. Of those flies, 75.9% had wild-type(red) eyes, and 24.1% had mutant(sepia eyes). Overall, more females were produced than males.
TABLE 1: F1 Generation Monohybrid Cross of Drosophila melanogaster (+se x...
References: Campbell, Neil A., Biology: Fourth Edition. Menlo Park: Benjamin/Cummings,
1996. "Genetics: Drosophila Crosses." Lab Handouts, General Biology Lab, 1996.
"So What 's a Monohybrid Cross Anyway?" Lab Handouts, General Biology Lab, 1996.
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