139hybrids studied. B–D associations occur somewhat more often than A–B associa-
tions in hybrids with rye, Ae. longisima , Ae sharonensis , or Ae. speltoides (Naranjo
1992 ; Naranjo and Maestra 1995 ; Maestra and Naranjo 1997 , 1998 ) but not in
hybrids with the allotetraploid Ae. geniculata (Cifuentes and Benavente 2009b ).
A recent genome assembly analysis of bread wheat and fi ve diploid related species
supports that both at the base-pair level as well as in gene content, the A and B
genome lineages are more similar to the D genome lineage than they are to each
other. The D genome is suggested to be originated from the A and B genomes
Fig. 6.1 Metaphase I pairing in Giemsa stained cells of hexaploid wheat. ( a ) Wild type wheat with
21 bivalents. ( b ) ph1b mutant wheat with four multivalents ( asterisks ) and 13 bivalents
6 The Mode and Regulation of Chromosome Pairing...