To study the cross between sepia eyed and red eyed Drosophila melanogaster mutants Introduction: Drosophila melanogaster, referred to by geneticists as the “Queen of genetics”, is a model organism to understand various genetic mechanisms due to its high fecundity, compact genome, easy and economical culture in labs and so on. It consists of three pairs of autosomes and a pair of allosomes. The male flies do not undergo meiotic recombination. The Drosophila genes are named after the phenotype that results when they are mutated.
Drosophila have a pair of compound eyes made of 760 ommatidia, with each containing 8 photoreceptor cells, cornea, pigment cells and support cells. Wild type flies have brick-red eyes which are considered dominant over other eye-colored flies like white, brown, sepia etc. Hypothesis: The cross between the red-eyed (wild type) flies and sepia eyed flies was conducted which can be represented as follows: SS x ss Red eyes v Sepia eyes.
P generation Ss Red eyes F1 generation F1 x F1 Ss x Ss v SS Ss Ss ss Red Red Red Sepia F2 generation The F1 flies are heterozygous dominant and when they are crossed the resulting red and sepia eye colored progeny in the F2 generation theoretically must be in the ratio 3:1 respectively. Results:
The lab experiment of mating of the wild type red eyed flies and sepia eyed mutants conducted resulted in 288 red eyed flies and 101 sepia eyed flies, which are ~ 3:1 in ratio. Discussion: The gene for the sepia eye color is located on the chromosome 3L with the sequence location 3L: 8, 513, 652.. 8, 514, 596(+). This gene codes for proteins and its molecular function includes pyrimidodiazepene synthase activity, glutathione transferase activity, glutathione dehydrogenase activity, transferring sulfur-containing groups, protein homodimerization activity, pteridine synthesis, eye pigment synthetic acitivity and so on.
The mutants for this gene are recognized by their eye color. The F1 flies were red eyed as their recessive nature was not expressed. But in the second filial generation the homozygous recessive progeny resulted. Conclusion: This mating follows the Mendelian principle according to which the paired genes that is, the allelic pairs separate from one another and are distributed to different sex cells.
The wild type gene for red eye color has a dominant effect over the gene for the sepia eye color and the recessive trait is masked in the F1 flies however, this trait reappears in one-fourth of the F2 generation. References Gardener, Simmons and Snustad – Principles of genetics VIII Edition John Wiley and Sons Flybase: a database of Drosophila genes and genomes http://flybase. org/reports/FBgn0086348. html Novitski, E, and S. Blixt. “Mendel, linkage, and synteny” Bioscience 28: 34-35