SATELLITE AND NUCLEOLAR NUMBER IN HYBRIDS BETWEEN RIBES NIGRUM AND R. GROSSULARIA AND IN THEIR BACKCROSSES

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Abstract
Studies of meiosis in allotetraploid blackcurrant-gooseberry hybrids and the relative uniformity of the C2 and C3 generations indicate that most functional gametes contain complete blackcurrant and gooseberry genomes. Backcrosses to 2x and 4x blackcurrants and to 2x and 4x gooseberries are presumed to give plants with 2:1, 3:1, 1:2 and 1:3 blackcurrant: gooseberry genomes respectively. Satellite number at metaphase in root tips of these hybrids and of the 2x F1''S is almost invariably the same as the number of gooseberry genomes present, although two satellite chromosomes occur in both blackcurrant and gooseberry. Presumably the blackcurrant satellite regularly disappears; it reappears when the parental genomes are separated by segregation. At late telophase-early interphase, the number of nucleoli is almost invariably the same as the number of metaphase satellites. Later, smaller additional nucleoli up to the number of blackcurrant genomes are seen in some cells. These facts are consistent with the theory that the larger nucleoli are formed on the gooseberry satellite constrictions and the smaller ones on the blackcurrant satellite constrictions. The vigour of the hybrids is not apparently associated with the functioning of the nucleolar chromosomes. The phylogenetic significance of differential amphiplasty is briefly discussed and its probable widespread occurrence noted.