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Drosophila

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INTRODUCTION
The fruit fly, Drosophila melanogaster, was used as a model organism to study the law of segregation and the law of independent assortment in Mendelian genetics. Drosophila was chosen as our model organism not only because of its short life cycle and fast breeding time but also because they are easy to maintain and handle in the laboratory. In this experiment a monohybrid cross and a dihybrid cross were performed.
The law of segregation establishes the concept of dominance. The law of segregation states that an individual organism possesses two alleles that can encode a trait and that these alleles separate when gametes are formed and one of the two alleles go into each gamete. The concept of dominance states that when two alleles that encode for a trait are present in an individual only the “dominant” trait will be observed. For a dihybrid cross these statements still hold true but the law of independent assortment can also be observed. This law states that alleles at different loci on a chromosome that encode for different things separate independently of one another.
METHOD
Before beginning the experiment it was important to determine the sexes of the flies using a dissecting microscope and then to predict which phenotypes would be expressed. To distinguish between the sexes it was helpful to observe size, shape, and color of the flies, and to also check for the existence of sex combs. Only male flies have sex combs. Female flies are usually somewhat larger than males and the caudal extremity is striped and tends to look sharp and protruding. The caudal extremity of male flies has a solid black tip at the end and is more round and blunt. For the monohybrid cross, male and female flies that were hybrids and had white eyes were crossed with male and female wild type flies that had red eyes. For the dihybrid cross flies that were displayed the

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