Elongated (E) and Five (F) are linked genes in a housefly that are 24 cM apart. The E allele produces elongated wings, which is dominant to the e allele that produces small wings. The F allele produces five stripes on the back of the fly, which is dominant to the f allele that produces four stripes. In a testcross of the progeny resulting from the cross EEFF × eeff, what proportion of the offspring should have elongated wings and five stripes?

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.