STATISTICAL EVALUATION OF LENGTH MEASUREMENTS ON BARLEY CHROMOSOMES WITH A PROPOSAL FOR A NEW NOMENCLATURE FOR SYMBOLS AND POSITIONS OF CYTOLOGICAL MARKERS

In 100 cells of an intergeneric Hordeum x Psathyrostachys hybrid, statistical evaluations were performed on length measurements of barley chromosomes and chromosome arms recognized by their Giemsa C-banding patterns for reliable identification. In 10 cells, we included the results of distance measurements between cytological markers and/or C-bands. Both actual and relative chromosome lengths as well as distances between cytological markers were distributed non-normally. Logarithmically transformed lengths proved to be normally distributed and were used to establish desirable statistical properties of mean values and confidence limits. No barley chromosome could be identified by length alone. Mean values of the logarithmically transformed distances between chromosome ends, constrictions, and Giemsa C-bands were back-transformed and used to construct an idiogram. The generally used nomenclature for chromosome markers and their positions based on C- or N-banding patterns was found arbitrary and inadequate. Instead, we propose a new, more general, informative and simple system for designating chromosome arms and cytological markers. It would be used as follows: (i) one chromosome arm with a specific banding pattern is designated the 'plus' arm and is depicted upwards in the idiogram; the other arm is designated the 'minus' arm; (ii) total genome length is defined as "one GeNome" (symbolized GN); (iii) distances on the idiogram are given in milliGeNomes (mGN), i.e., thousandths of a GN; (iv) the centromere is given the position 0; and (v) cytological markers on the 'plus' and 'minus' arms are designated by their positive and negative distances in mGN from the 0-position, respectively.