Cytogenetics of a Crown Rust‐Resistant Hexaploid Oat with 42 + 2 Fragment Chromosomes¹

Abstract

Twenty‐two bivalents were observed in X117 oat (Avena sativa L.), a isogenic line resistant to crown rust (Puccinia coronata Cda. avenae Fraser and Led.), and with 42 + 2 fragment chromosomes. The homologous fragment chromosomes are either telocentric or acrocentric. Transmission through the egg, calculated from the backcross data, was 18.2%. A dominant gene, Pc‐15, conferring resistance to races 264 and 290 of crown rust of oats is located on each of the fragments.

B Chromosome Polymorphism in Maize Landraces: Adaptivevs. Demographic Hypothesis of Clinal Variation

“…Some effects of the B chromosomes appear to be attributable to the products of their genes, as is the case with genes controlling resistance to rust in the B chromosomes of Avena sativa (Dherawattana and Sadanaga 1973) and with the genes conferring resistance to antibiotics in the B chromosomes of the fungus Nectria haematococca (Miao et al 1991). Maize B chromosomes are highly repetitive in nature and share the vast majority of their sequences with the regular complement (Peacock et al 1981;Lin 2003, 2004).…”

Cancer Karyotypes: Survival of the Fittest

“…The mechanism responsible for maintaining B-chromosomes in the karyotype is still debated (Camacho et al, 2000), but it is clear that, at least in some cases, B-chromosomes can act heterotically (i.e., enhance fitness) and confer an adaptive advantage to the individual carrying them compared to individuals whose karyotype lacks B-chromosomes, much like aneuploidy in yeast grown under stressful conditions. For instance, Avena sativa with B-chromosomes shows resistance to rust (Dherawattana and Sadanaga, 1973) and the fungus Nectria haematococca with B-chromosomes is resistant to antibiotics (Miao et al, 1991a,b). Similarly, the plant Allium schoenoprasum with B-chromosomes displays higher survival rates in natural environments than A. schoenoprasum without B-chromosomes (Holmes and Bougourd, 1989), due to the ability of B-chromosomes to enhance the germination rate in drought conditions (Plowman and Bougourd, 1994).…”

The B-chromosome polymorphism of the grasshopper Eyprepocnemis plorans in North Africa: II. Parasitic and neutralized B1 chromosomes

“…The heterotic model (White, 1973), however, argues that B chromosomes lacking drive may be maintained because of their beneficial effects on the fitness of individuals carrying small number of Bs. Some B chromosomes are good candidates to be heterotic since they have an obvious beneficial effect on carrier fitness (eg, Nectria haematococca (Miao et al, 1991a, b) and Avena sativa (Dherawattana and Sadanaga, 1973)), but their population dynamics has been analysed only in Allium schoeno- Correspondence: Dr M Bakkali, Departamento de Genética, Facultad de Ciencias, Universidad de Granada, 18071, Granada, Spain. E-mail: mbakkaliȰugr prasum, where Bs lack drive and are beneficial in increasing viability from seed to seedling (Holmes and Bougourd, 1989;Plowman and Bougourd, 1994).…”