8. Dioxin (in the human diet!) and ethidium bromide (used in labs to see DNA using UV light) are classified as because they insert themselves in between adjacent DNA bases. 9. UV light can cause two adjacent pyrimidines to form a (Fig 18.21). 10. Study Figure 18.26. What is the difference between black, green and red grapes relative to expression of genes that produce anthocyanin pigments? Possible answers: retrotransposon prevents pigment expression; partial removal of retrotransposon allows partial pigment expression; absence of retrotransposon allows normal pigment expression. a. Black: b. Green : c. Red:.