In this particular experiment, the focus was on eye color mutations, resulting from mutations on the genes affecting pigmentation. .
Several tests can be used to differentiate the different eye mutant stocks of fruit flies according to phenotype and genotype. Generally, the first objective is to determine the mode of inheritance of the mutant. By examining the first and second filial generations (F1 and F2), this can be done relatively easily. The results of these genetic crosses can aid in the determination of the number of genes involved in the mutation, and whether the mutation is autosomal or sex-linked, and recessive or dominant. These characteristics are in conjunction with two principles that Gregor Mendel proposed in the 1800's, defining patterns of segregation of gametes and inheritance of progeny. Mendel's first law, the Principle of Segregation, states that members of each pair of alleles of a gene separate when gametes are produced in meiosis. Mendel's second law, the Law of Independent Assortment, predicts that pairs of alleles will separate independently from each other during gamete formation. .
To classify D. melanogaster into phenotypic groups based on sex, a dissecting microscope can be used. Males and females are distinguished on the basis of three basic differences- genitalia, coloring, and examination of the front legs. Heavy dark bristles surround the male genitalia, while the female genitalia have none. The coloring of the abdomen of the males differs from the females in that there is a heavily pigmented tip on the posterior, as opposed to the transverse stripes found on the female. Lastly, only in males can one see the presence of sex combs on the fore legs (Carolina Drosophila Manual, Carolina Biological Supply Company.) .
While the classification of sex is rather basic, classifying an unknown mutant stock is somewhat more complicated. One method is to determine on which of the fly's four chromosomes the individual fly mutation occurs.