New HindIII, RsaI and TaqI restriction fragment length polymorphisms (RFLPs) within the haemopoietic cell kinase gene in chromosome band 20ql 1.2 are described. These RFLPs provide a useful marker for linkage analysis in proximal 20q. Source~description. priCK contains a 2.1-kb insert from the haemopoietic cell kinase (HCK) oncogene cloned into pUC18. Double digestion with EcoRI and PstI releases insert fragments of approximately 1.0, 0.8 and 0.2 kb. Polymorphisms. A 800-bp probe from the 5" half of priCK detects HindIII and RsaI restriction fragment length polymorphisms (RFLPs), whereas a 1000-bp probe from the Correspondence to: P. E. Hollings 3" half of priCK detects a TaqI RFLP at this locus. Each RFLP comprises two alleles (Fig. l) whose sizes are: HindIII, A1 (27.0 kb), A2 (21.0 and 6.3 kb); RsaI, B1 (2.0 kb), B2 (1.3 and 0.7 kb); TaqI, A1 (1.4 kb), A2 (1.2 kb).
Enzymes not detecting polymorphisms at this locus in a panel of 10 unrelated Caucasians included BamHI, BglII, EcoRI, MspI and PstI.
Frequencies. These are given in Table 1.
Each RFLP conformed to Hardy-Weinberg equilibria (P > 0.05). The population sampled consisted of unrelated Caucasians.
Chromosomal localization, priCK has been assigned to chromosome region 20qll.2-q12 by radioactive in situ hybridization to metaphase chromosomes (Quintrell et al.