After generating all the Dp(1;Y)BSC chromosomes as described in FBrf0212582, we calculated the minimal euchromatic coverage of the X chromosome provided by these duplications as 97.0%. There are three remaining small gaps in duplication coverage: 1. Between the proximal end of Dp(1;Y)BSC74 and other duplications derived from In(1)BSC3 and the distal end of Dp(1;Y)BSC158. The maximum possible extent of this unduplicated portion of the X chromosome is 3E4, X:3583172 to 3F9, X:3843899 (Release 5). 2. Between the proximal end of Dp(1;Y)BSC325 and other duplications derived from In(1)BSC32 and the distal end of Dp(1;Y)BSC185. The maximum possible extent of this unduplicated portion of the X chromosome is 11E8, X:13178324 to 12A9, X:13518037 (Release 5). 3. Between the proximal end of Dp(1;Y)BSC231 and other duplications derived from In(1)BSC27 and the distal end of Dp(1;Y)BSC223. The maximum possible extent of this unduplicated portion of the X chromosome is 13C5, X:15392986 to 13D3, X:15464027 (Release 5). We used 22420000 as the total number of base pairs in X euchromatin in our calculation.