A heterozygous female will always display the dominant wild-type gene if present. The uncertainty of female genotype is cleared by the acquisition of an F0 stock which is homozygous dominant or recessive. Determining Sex Aside from determining eye colour, recognising the sex of D. melanogaster was paramount to this experiment. This can be accomplished by observation of the unconscious flies through the dissecting microscope. Males are distinguishable by the presence of heavy dark bristles surrounding the male genitalia, bristles not present on the females.
Examination of the front legs provided another distinction, as males carry a sex comb which females do not. Size and shape cannot be used to determine sex as both vary depending on age. The abdomen of an older male will be darker than that of an older female; however abdominal colour also varies with age, making it an unreliable method of sexing. Life Cycle Observed throughout the experiment were four life stages of D. melanogaster. Eggs hatch a day after being laid by the female, and are in 1st instar larval form. Over the next 6 days, the larvae would molt to the 2nd and 3rd instar.
The cuticle of the 3rd instar hardens into a pupa, and after 6 days in the puparium, metamorphosis is complete and the adult fly forces its way through the anterior end of the puparium. Older males would attempt to mate with very young females; therefore it was important to be vigilant in removing all adult flies prior to the emergence of the newest generation. This was done at one week intervals. The flies were raised in vials with a commercially available medium supplying all nutrients, with a new medium prepared for each new generation. Handling D. elanogaster First and foremost in the handling of Drosophila melanogaster was to ensure that the specimens were not exposed to condensation at any time, as this is fatal to the flies. Transportation, examination and counting were all accomplished with the flies unconscious, a reaction triggered by cold temperatures. Vials containing the specimens were put on ice for five minutes, and during examination under a microscope, the sorting plate was placed over a petri dish filled with ice. Once unconscious, flies were sucked into vials with an aspirator.
Care was taken at all times to be gentle with the specimens, and a sable paintbrush was used to move the specimens around to avoid damage, however those that were damaged were discarded into a supplied oil jar (morgue). Experimental Procedure For the small population group, a population of four males and four females was established, two of each eye colour per sex. All eight flies were placed in the culture vial still unconscious after sexing (care must be taken to keep the vial on its side until all specimens are conscious, or the flies will become stuck to the medium), and the culture vials stored at room temperature for a week.
For the large population group, an initial population of 40 was established. This population consisted of 20 males and 20 females, 10 of each eye colour per sex. The same procedure was followed as with the small population. After a one week period, the initial population was removed from the two vials, the eight parents from the small population and the 40 parents from the large population. One week after the removal of the parents, the first data was recorded. Eight flies (four male, four female) were randomly removed from the small population, and 40 flies (20 male, 20 female) were randomly removed from the large population.