Exp 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 Results 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 Results Parent Description Female Phenotype Male Genotype Ebony Bodied flies Wild Bodied flies female male female male 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 Wild Female Ebony Body Female Wild Male Ebony Body Male Total Total Total Wild flies Total Total Total Ebony flies Fly ratio Wild Ebony Table 2 Hybrid Cross F1 Cross Results Hybrid Description Female Phenotype Aim To examine the inheritance of the single mutant gene for ebony body colour in three generations of Drosophila melanogaster flies Male Genotype Wild Bodied flies Ebony Bodied flies Procedure 1 2 3 4 5 6 7 8 24 Click on the Reset then Select buttons and select Saved Parents Select Exp03 f mfp or Exp03 m mfp f m are the mutant s sex Drag each of the parents over to the Observation Platform and record their phenotype and genotype in the first table Click the Breed button and record each offspring s phenotype During recording drag a male and female offspring into the Hold Jar Empty the Parent Offspring area after counting 50 100 offspring 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 Record the phenotypes of 200 offspring then answer the questions Drosophila Genetics Lab Newbyte Educational Software Total Wild flies Total Ebony flies Fly ratio Wild Ebony Newbyte Educational Software Drosophila Genetics Lab 25 Discussion Questions 1 Complete the following table which deals with the original parentcross between a homozygous wild individual and a homozygous ebony winged individual Parent Female Male Phenotype Genotype Genotypes of gametes 6 Complete the following table which deals with the hybrid cross between two heterozygous individuals Parent Female Male Phenotype Genotype Genotypes of gametes 7 Complete the Punnett Square below for the hybrid cross or F1 cross phenotype Female 2 Complete the Punnett Square below for the homozygote cross Parent cross phenotype Female Male GAMETE genotypes genotype Male GAMETE genotypes genotype phenotype genotype phenotype genotype From the Punnett Square above what is the expected ratio of NORMAL flies to ebony bodied flies 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 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 Questions 26 Drosophila Genetics Lab Newbyte Educational Software Newbyte Educational Software Drosophila Genetics Lab 27