© Newbyte Educational Software24Drosophila Genetics Lab © Newbyte Educational Software25Drosophila Genetics LabExp 3 Single Gene Inheritance Name : ___________________________ Date:______________Introduction In this experiment we will examine the inheritance of a single gene which governs body colour in Drosophila melanogaster fruit flies. The gene is found on the third chromosome of our flies and normally results in the fly having an orange body. However, a mutant allele has been found which causes the body to darken. This colour is called ebony and the allele causing the change is called the ebony body allele.As wild body colour is dominant to ebony, a heterozygous fly will possess a wild body phenotype. The symbol used for the wild allele is Eb and the mutant eb. Aim To examine the inheritance of the single mutant gene for ebony body colour, in three generations of Drosophila melanogaster flies.Procedure1. Click on the Reset then Select buttons and select Saved Parents.2. Select Exp03_f.mfp or Exp03_m.mfp. (f & m are the mutant’s sex)3. Drag each of the parents over to the Observation Platform and record their phenotype and genotype in the first table.4. Click the Breed button and record each offspring’s phenotype.5. During recording, drag a male and female offspring into the Hold Jar.6. Empty the Parent/Offspring area after counting 50 - 100 offspring.7. Drag the held flies into the Parent area and breed them before you examine and record them in table 2. They are still offspring until they are bred and so their genotype may not be visible.8. Record the phenotypes of 200 offspring, then answer the questions.WildFemaleEbony BodyFemaleWildMaleEbony BodyMaleResults Record the results observed in the following tables, by placing a stroke in the appropriate column, as each offspring is displayed.Table 1 Parent-Cross ResultsParent DescriptionFemale Phenotype - Genotype -Male “ - “ -Wild Bodied fliesEbony Bodied fliesfemale male female maleTotal = Total = Total = Total =Total Wild flies = Total Ebony flies =Fly ratio Wild : Ebony _______:_______Table 2 Hybrid-Cross (F1 Cross) ResultsHybrid DescriptionFemale Phenotype - Genotype -Male “ - “ -Wild Bodied fliesEbony Bodied fliesTotal Wild flies = Total Ebony flies =Fly ratio Wild : Ebony _______:_______© Newbyte Educational Software26Drosophila Genetics Lab © Newbyte Educational Software27Drosophila Genetics LabDiscussion Questions 1) Complete the following table, which deals with the original parent-cross, between a homozygous wild individual and a homozygous ebony winged individual. Parent Phenotype Genotype Genotypes of gametes Female Male 2) Complete the Punnett Square below for the homozygote-cross (Parent-cross). phenotype:__________________________ genotype :____________________ GAMETE genotypes phenotype: ______________________________genotype: _______________3) By referring to the Punnett Square above, what would you expect the ratio of wild flies to ebony flies to be? _______ : _______ 4) How well does the ratio of wild : ebony bodied flies observed in the experiment compare to the ratio predicted by the Punnett Square? Why?_________________________________________________________________________________________________________________________________________________________________________________5) Why are there usually differences between the number of males and the number of females observed in a random sample of flies?___________________________________________________________6) Complete the following table, which deals with the hybrid-cross, between two heterozygous individuals. Parent Phenotype Genotype Genotypes of gametes Female Male 7) Complete the Punnett Square below for the hybrid-cross(or F1 cross). phenotype:__________________________ genotype :____________________ GAMETE genotypes phenotype: ______________________________genotype: _______________From the Punnett Square above, what is the expected ratio of NORMAL flies to ebony bodied flies? _______ : _______ What are the expected ratios of genotypes? (EbEb : Ebeb : ebeb) _______ : _______ : _______ 8) How well does the ratio of wild : ebony winged flies observed in the experiment compare to the ratio predicted by the Punnett Square?___________________________________________________________9) Why would you expect a difference, between the observed and predicted phenotypic ratios?______________________________________________________________________________________________________________________Additional