Chromosome identification and nomenclature of Sorghum bicolor

Abstract

Linkage group identities and homologies were determined for metaphase chromosomes of Sorghum bicolor (2n = 20) by FISH of landed BACs. Relative lengths of chromosomes in FISH-karyotyped metaphase spreads of the elite inbred BTx623 were used to estimate the molecular size of each chromosome and to establish a size-based nomenclature for sorghum chromosomes (SBI-01-SBI-10) and linkage groups (LG-01 to LG-10). Lengths of arms were determined to orient linkage groups relative to a standard karyotypic layout (short arms at top). The size-based nomenclature for BTx623 represents a reasonable choice as the standard for a unified chromosome nomenclature for use by the sorghum research community.

Figure 1.—

Simultaneous FISH of a 17-BAC cocktail probe to sorghum mitotic metaphase chromosome spread. The patterns of signals enable FISH-based recognition of each chromosome pair and associate specific linkage groups with specific chromosomes. Each letter corresponds to a linkage group (Menz et al. 2002).

Figure 2.—

Correlation between mitotic metaphase chromosomes and linkage groups of sorghum using the map of Menz et al. (2002). Asterisks denote signals from the 17 BACs shown in Figure 1. Chromosomes are numbered according to size and linkage groups are labeled alphabetically. Chromosomes are depicted with the shorter arm in the top position. BAC clones are positioned on the ideogram according to their positions relative to the centromeres. Bar indicates 1.5 μm for metaphase chromosomes and 50 cM for linkage maps.