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In your experiments with Drosophila, you found that the wildtype allele that codes for grey adult insects is sometimes mutated, with mutants having a black colour. Similarly, you find that your population has alleles that code for vestigial wings instead of the wildtype normal wings. (Both mutations are recessive.) You want to know whether the two genes for body colour and wings are linked. In your preliminary crosses you have established a large number of individuals that you require for testcrosses.
9a. Which two genotypes will you use for the testcross? (Hint: One of the two genotypes should be a heterozygous dihybrid.) Use the common wildtype notation (e.g., “ar+ tg”) rather than the allele notation (VvZZ). For simplification, disregard the gender. (2)
9b. Indicate the two phenotypes of your testcross. (1)
9c. Indicate the genotypes of the progeny (next generation) of the testcross by drawing a Punnett square. (3)
Assuming a total number of 4400 flies for the progeny generation, what are your expectations for the ratio of genotypes if
9d. the two genes are linked? (1)
9e. the two genes are not linked? (1)
9f. Finally, if the two genes are not linked according to your results, would you expect that they lie on different chromosomes? Explain your answer. (2)
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