Figure 1.—

Genetic cross and screen for Y, rDNA deletions. In generation 0, females harboring a heat-shock-inducible I-CreI nuclease are mated to males with a recently isogenized yellow⁺-marked Y chromosome. Males were heat-shocked as larvae and crossed to a common yellow white stock en masse in generation 1. Collecting individual males in generation 2 allowed us to sample independent I-CreI-induced rDNA events of the Y chromosomes. Males were crossed to both fresh yellow white females to establish a stock and to C(1)DX females, whose compound-X chromosome lacks rDNA, to determine if damage to the rDNA had occurred. Damage could be assessed as an altered female-to-male ratio (at an extreme, 0:1) or as bobbed female phenotypes (in generation 3). In every subsequent generation, males were backcrossed to the maternal genotype (yellow white) to maintain the stock and C(1)DX females to retest the rDNA array. Genetic nomenclature: hs-I-CreI is P{v^+t1.8=hs-I-CreI.R}2A, v¹; y w is y¹ w^67c23; Y10 is y⁺Yw⁺, Dp(1;Y) y⁺, P{w⁺=RSw}10A, or y⁺Yw⁻, Dp(1;Y) y⁺, P{w⁻=RSw⁻}10B; and C(1)DX is C(1)DX, y¹ f¹ bb⁰.