Robertsonian polymorphism between RYHyb25 and RYHyb29. (a) Linkage groups RYHyb25 and RYHyb29 represent acrocentric chromosomes in Female 1 and Male 2 while RYHyb25_29, a metacentric chromosome, represents a fusion between the two acrocentric chromosomes in Male 1 and Female 2. Chromosome (Omy), linkage group (RT), and putative centromere (c) location for each locus mapped in Guyomard et al. (2006) is indicated. Map distances are in centiMorgans. (b) Possible diploid chromosome constitutions for the Omy25 and Omy29 Robertsonian polymorphism in the rainbow trout (RBT) parent stock (acrocentric, 2 N = 60; heterozygous, 2 N = 59; or metacentric 2 N = 58) and the Yellowstone cutthroat trout (YCT) homologues (YCT25 and YCT29). RBT chromosomes are in white and YCT chromosomes are in black. (c) Inferred diploid chromosomal constitutions for F1 hybrid parents. YCT crossed by RBT with either the acrocentric or heterozygous polymorphism would yield RYHyb25 and RYHyb29 in Female 1 and Male 2, and YCT crossed by RBT with either the metacentric or heterozygous polymorphism would yield RYHyb25_29 in Male 1 and Female 2.