Chaolan Fan,Ming Hao,Zhenyu Jia, Christian Neri, Xue Chen, Wenshuai Chen, Dengcai Liu, Adam J. Lukaszewski
Allopolyploid wheat (Triticum aestivumL.) carries three pairs of homoeologous genomes but its meiotic pairing is diploid‐like. This is the effect of thePh(pairing homoeologous) system which restricts chromosome pairing to strictly homologous.Ph1is the locus with the strongest effect. DisablingPh1permits pairing between homoeologues and is routinely used in chromosome engineering to introgress alien variation into breeding stocks. Whereas the efficiency ofPh1and the general pattern of homoeologous crossovers in its absence are quite well known from numerous studies, other characteristics of such crossovers remain unknown. This study analyzed the crossover points in four sets of theph1b‐induced recombinants between wheat homologues as well as between three wheat and rye homoeologous chromosome arms, and compared them to crossovers between homologues in a reference wheat population. The results show thePh1locus also controls crossing over of homologues, and the general patterns of homologous (withPh1) and homoeologous (withph1b) crossing over are the same. In all intervals analyzed, homoeologous crossovers fell within the range of frequency distribution of homologous crossovers among individual families of the reference population. No specific DNA sequence characteristics were identified that could be recognized by thePh1locus; the only difference between homologous and homoeologous crossing over appears to be in frequency. It is concluded that thePh1locus likely recognizes DNA sequence similarity; crossing over is permitted between very similar sequences. In the absence ofPh1dissimilarities are ignored, in a proportion to the level of the sequence divergence.