Drosophila melanogaster is a species of fruit fly. Scientists have studied the inheritance patterns of many genetic traits in fruit flies. To carry out genetic crosses with fruit flies: - a specimen tube is prepared with food for the fruit flies, as shown in Fig. 1.2 - adult male and female fruit flies are added to the specimen tube to allow mating to take place - the specimen tube is kept in warm conditions for several days - the eggs laid by female fruit flies develop into pupae - adults are removed from the specimen tube before pupae mature into adult fruit flies - offspring emerge as adult flies $$\(10-15\)$$ days after eggs are laid. One of the genetic traits studied in fruit flies is eye colour．The normal（wild type）eye colour of D．melanogaster is red． Eye colour in D．melanogaster is controlled by several genes，including two genes that are located on separate chromosomes， $$\(\mathbf{A} / \mathbf{a}\)$$ and $$\(\mathbf{D} / \mathbf{d}\)$$ ． －Allele A is dominant to allele a． －Allele D is dominant to allele d． （a）A student was provided with two populations of fruit fly： －brown－eyed fruit flies with genotype AAdd －scarlet－eyed fruit flies with genotype aaDD． In each population，males and females were provided in separate specimen tubes． The student decided to carry out two genetic crosses． The first cross used fruit flies from the initial populations to produce offspring that are heterozygous for each of the two genes（double heterozygotes）． The second cross used the double heterozygotes produced from the first cross． To carry out the genetic crosses，the student was provided with standard laboratory equipment and： －specimen tubes containing food －a chemical to anaesthetise the flies－this chemical，when given at a particular dose， makes the flies immobile for more than 30 minutes －small brushes for sorting immobile flies without harming them． （i）Identify a hazard in this investigation and state a risk associated with the hazard and state one precaution that the student should take． . . ［1］ (ii) Describe a method the student could use to carry out: - the first cross using fruit flies from the initial two populations to produce double heterozygotes (genotype AaDd) - the second cross using the double heterozygotes produced from the first cross - an analysis of the offspring phenotype ratio from the second cross. The description of your method should be set out in a logical way and be detailed enough for another person to follow. The method should include a description of how offspring phenotypes would be identified. . . . . . . . . . . . . . . . . . . . . (iii) Predict the ratio of offspring phenotypes from the cross between parents that are heterozygous for the two genes (AaDd). You may use this space for any working. ratio phenotypes

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