Figure 7

Models for the origin of p1-ww[4Co63]. Various models may help explain the evolution of p1-ww[4Co63]. Notice that the same color code is used here as in Figure 3, which illustrates schematic alignment of p1 and p2 alleles. (A) Expansion and contraction of the p locus generates P1-wr[B73] and p1-ww[4Co63], respectively. A simplified representation of the P1-wr[B73] cluster is shown. Unequal crossing over between p2/p1[B73] (or p2) and p1/p2[B73] could have caused the deletion of the internal P1-wr[B73] repeats. Such a recombination event could have occurred any time during the evolution of the cluster, independent of the P1-wr copy number, retroelement insertions at the 3' end and the deletion at the p2/P1-wr junction sequence. (B) Similarly, alignment along the retrotransposon cluster and crossover between P1-rr and P1-wr[B73] could have generated the p1-ww[4Co63] structure. (C) A misalignment at the repeat sequences of P1-rw- like alleles, which contained the simple P1-wr[B73] distal enhancer region, and unequal crossover could have led to a duplication or deletion event giving rise to p1-ww[4Co63]. However, this model does not account for the Shadowspawn retroelement in p1-ww[4Co63].