Deletion at the endogenous Crk locus (should result in deletion of almost the entire open reading frame, from 48bp 5' of the ATG start codon to 121bp 5' of the TAA stop codon, based on the homology repair template used). A Disc\RFPDsRed(T1).3xP3.cHa marker has been inserted in place of the deleted sequence; since there is essentially no recombination on the fourth chromosome, this means that the CrkdsRed chromosome can serve as a 4th chromosome balancer, as it is both recessive lethal (due to CrkdsRed) and causes a dominant scorable phenotype (due to the Disc\RFPDsRed(T1).3xP3.cHa marker).