Drosophila melanogaster is a small fruit fly that is often used in research on genetics. Wild fruit flies normally have dark red eyes due to the presence of a brown pigment, ommochrome, and a bright red pigment, drosopterin. Fig. 2.1 shows an adult female fruit fly and an adult male fruit fly. A biologist carried out an investigation to determine the roles of two genes that are involved in the determination of eye colour in adult fruit flies. Both genes have two alleles. Earlier research by other scientists suggested that: - the synthesis of the brown pigment ommochrome depends on the gene $$\(\mathbf{B} / \mathbf{b}\)$$ - the synthesis of the bright red pigment drosopterin depends on the gene $$\(\mathbf{R} / \mathbf{r}\)$$. The biologist obtained the parent fruit flies shown in Table 2.1. The biologist carried out the procedure shown in Fig. 2.2 to cross the parent fruit flies and obtain first generation offspring. Suggest a reason why the biologist removed the parent fruit flies from the specimen tubes on day 7 . ............................................................................................................................................... . ............................................................................................................................................... . ......................................................................................................................................... The biologist wanted to cross the first generation of fruit flies with one another to produce the second generation of fruit flies. The first generation of adult fruit flies in the specimen tubes on day 12 were a mixture of females and males and had not yet mated. The biologist crossed the first generation of fruit flies with one another by: - preparing fresh specimen tubes in which to produce the second generation of fruit flies - using a chemical to anaesthetise the first generation of adult fruit flies so that they were temporarily unable to move - separating the adult female fruit flies and adult male fruit flies - placing four adult female fruit flies and four adult male fruit flies into each of the fresh specimen tubes.

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