A genetic study on penetrance and expressivity for Bar gene in Drosophila melanogaster

Drosophila melanogaster (fruit fly) is commonly used as a model organism because it has significant properties such as short life cycle, abundance in genetic variations, relative inexpensiveness, and small body size. The Mendelian trait, eye shape, was chosen in the study. The bar eye (Bar) shape was compared to the round eye shape. A cross (bar × round) and its reciprocal cross (round × bar), the corresponding F1 and F2 generations were created according to the mating maps. The goodness of fit test for the observed data against the theoretical genotypic ratios was analyzed using χ2 statistical test. The results showed that the observed values for Bar gene in male and female of both crosses fit the theoretical genotypic ratios because the χ2 values were much smaller than the critical χ2 value (3.84) at 5% significant level. For Bar gene, the penetrance was complete in male of both crosses. This was due to the hemizygous status. However, the incomplete penetrance and variable expressivities were observed in female of both crosses. In bar × round, when Bar was in homozygous status, the penetrance was 53.0%. In the heterozygotic status, the varied expressivities were 53.0% of bar eye and 47.0% of dent eye, respectively. In round × bar, the Bar gene in homozygous status demonstrated 0.0% penetrance. The expressivities displayed 0.0% of bar eye and 100.0% of dent eye, correspondingly. The allelic interaction was the cause for the incomplete penetrance and different expressivities of the gene. The finding provided a foundation for studying the interaction between Bar gene and other genes.