Figure

Plate 2.1. The advances in chromosome staining and in situ hybridisation methods greatly facilitated chromosome manipulation and crop improvement. (A) Conventionally stained T. durum mitotic metaphase chromosomes show similar chromosome size and arm ratios and thus individual chromosome identification is impossible (black age). (B) The same cell after C-banding (Gill and Kimber 1974; Gill et al. 1991), which produces a pattern of dark (heterochromatic) and light (euchromatic) bands along the chromosomes that is chromosome-specific and allows identification of individual chromosomes (black and white age). Note the C-banding identified the wheat–rye whole arm translocation T1RS·1BL (marked by arrows) in this line conferring resistance to leaf, stripe, stem rust, powdery mildew and also has a heterotic effect on grain yield because it also confers a large root mass. (C) Genomic in situ hybridisation (GISH) of the T1RS·1BL durum germplasm using total genomic rye DNA as a probe labelled with rhodamine together with an excess amount of unlabelled genomic wheat DNA; note the rye chromosome arm is detected by red fluorescence (marked by arrowheads), whereas wheat chromosomes are counterstained with DAPI and fluoresce blue (colour age). C-banding and GISH are powerful methods for monitoring alien chromatin in wide hybridisation. (D) C-banding and GISH patterns of radiation-induced terminal and interstitial wheat–rye translocations conferring resistance to Hessian fly, H21: T6BS·6BL-6RL, T4BS·4BL-6RL, Ti4AS·4AL-6RL-4AL documenting the amount and position of introduced rye chromatin in wheat chromosomes. Source: Friebe et al. (1996), fig. 29. (E) Fibre-fluorescence in situ hybridisation (Fibre FISH) images of extrachromosomal circular DNA molecules (eccDNAs) in glyphosate-resistant Amaranthus palmeri; upper insert: linear form of eccDNA; lower insert: dimerised circular form of eccDNA with head-to tail tandem orientation (#1, BAC 01G15; #2, BAC 13C09; #3, BAC 22F22; #4, BAC 23A10; #5, BAC 03A06; #6, BAC 08H14). Source: Koo et al. (2018), fig. 2b, c). Fibre FISH can visualise naked DNA molecules, the above experiment demonstrated novel eccDNA molecules controlling a glyphosate resistant trait. (F) Single-gene FISH patterns using homoeologous group-1 probes to mitotic metaphase chromosomes of Aegilops umbellulata; note that the 1L-3 probe hybridises to a distal region of the group-6 Ae. umbellulata chromosome, indicating the presence of an interchromosomal translocation. Source: Danilova et al. (2014), fig. 4b). Single-gene FISH allows rapid determination of gene synteny, which is the first necessary first step in alien introgression. (G) GISH analysis of introgression library of alien chromatin from chromosome 5Mg (labelled green) of Aegilops geniculata into wheat chromosome 5D (red). (H) Identification of wheat B-genome telocentric chromosomes using multicolor FISH probed with CL191 (red), GAAn (green) and CRWs (white), note that the FISH signals of CL191 were located in telomeric regions of 2BL, 3BL, 7BL and 7BS, whereas the signals for CRWs were located in the centromeric region of all the B-genome telosomes except 1BS and 6BS. Source: Koo et al. (2016), fig. 2b).