A CRISPR construct called P{white-eraser} may be used to eliminate the miniwhite marker from transgenes through simple crosses. As shown in the figure below, P{white-eraser} has four components.

1. The GFP gene driven by 3xP3 regulatory sequences to enable one to track P{white-eraser} in crosses by GFP expression in the eye.
2. The Cas9 gene expressed ubiquitously under the control of Act5C regulatory sequences.
3. Sequences encoding guide RNAs directed at miniwhite expressed ubiquitously under the control of U6 regulatory sequences.
4. A repair template with homology arms corresponding to miniwhite that enables a 3xP3-DsRed cassette to be inserted into miniwhite.

As shown in the figure, two results may be obtained when P{white-eraser} is combined with miniwhite-marked transgenes in crosses.

1. If homology-directed repair occurs, the 3xP3-DsRed cassette is inserted into miniwhite.
2. If nonhomologous end joining occurs, a mutation (shown as mini-w*) is generated in miniwhite, but the 3xP3-DsRed cassette is not inserted.

P{white-eraser} and its use were described in Liu et al. (2020) “Rapid Release of Ca[2+] from endoplasmic reticulum mediated by Na[+]/Ca[2+] exchange” The Journal of Neuroscience 40: 3152–3164.