Fig. 1. Effects of Ph1 on chromosome pairing at meiosis in bread wheat haploids (2n = 3x = 21; ABD genomes). Pollen mother cells (PMCs) with and without Ph1 are shown. (A) PMC with Ph1 showing 1 rod II and 19 I. Such a superficial pairing in the presence of Ph1 has been called "chromosome dating." (B) PMC of a ph1b-haploid showing 6 II (3 ring and 3 rod bivalents) + 9 I. Note extensive homoeologous pairing because of the absence of Ph1. Interestingly, one gene can make such a difference. (Fig. 1B from Jauhar et al., 1991).