Huang L and Gill BS (2001) An RGA-like marker detects all known Lr21 leaf rust resistance gene family members in Aegilops tauschii and wheat Theoretical and Applied Genetics 103:1007-1013.
Fritz A MAS Wheat. Bringing Genomics to the Wheat Fields. Disease resistance. Leaf Rust Resistance. Lr21 MAS Wheat. Marker Assisted Selection in Wheat.
Talbert et al developed an easier to use PCR marker based on the sequence of clone KSUD14. The primers were designated D14-L and D14-R (see ref. TAG-87-789).
When a translocated alien fragment is in a wild-type Ph1 background it no longer recombines with wheat chromatin (or only at very low frequencies). Therefore, the segment is inherited as a whole, so if there is a molecular marker located within the fragment containing the translocated gene, the genetic distance to the gene would be zero, even when the physical distance could be very large.