My life with Hordeum chromosomes
Ib Linde-Laursen
dept. Agriculture and Ecology, Copenhagen University
The genus Hordeum (Barley) belongs to the tribe Triticeae of the Poaceae. The tribe comprises the cereal crops wheat, barley and rye and many important forage grass species, in all about 350 species. The genus Hordeum includes 32 species and altogether 45 taxa occurring in temperate regions of the world except in Australia. Relatively most species are found in South America. The species have 14, 28 or 42 large chromosomes in somatic cells. The chromosomes, excepting those wearing ‘satellites’ are morphologically so similar within chromosome complements (karyotypes) that they can only be identified reliably using special procedures producing patterns of cross-bands in the chromosomes. In the inbreeding Hordeum vulgare (cultivated barley) use of Giemsa C-banding demonstrates 7 different banding patterns, each pattern occurring in two of barley’s 14 chromosomes, i.e. in one of the 7 pairs. The bands may vary in size and position although not to a degree which renders it impossible to recognize the basic banded karyotype of H. vulgare in barley lines (varieties). Banding patterns may establish the parental origin of their chromosomes. Bands show Mendelian segregation and can be used to assign genes to chromosome regions. Each of the 45 Hordeum taxa has its specific basic banded karyotype, but this may not be so dissimilar relative to those of other taxa that it is possible to distinguish taxa on this basis. Interspecific hybrids among H. vulgare and Hordeum taxa with 28 or 42 chromosomes may show partial or complete elimination of 7 chromosomes, generally those of H. vulgare corresponding to one genome. Based on chromosome elimination patterns a hypothesis is put forward that the chromosomes have an orderly arrangement within the genome. In hybrids with the related Psathyrostachys fragilis (14 chromosomes) and in the interspecific Hordeum hybrids, the H. vulgare chromosomes are on an average lying closer to the cell centre than the chromosomes of the other parent supporting that the two genomes occupy different compartments.
