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Chromosome Pairing, Structural Hybridity, and Fragments in Rosa

1933; University of Chicago Press; Volume: 94; Issue: 3 Linguagem: Inglês

10.1086/334327

1940-1205

Eileen Whitehead Erlanson,

Plant Reproductive Biology

1. Multiple pairing of chromosomes due to reduplication and reciprocal translocation of segments has been found in diploid roses belonging to the species complexes Rosa multiflora, R. blanda, R. woodsii, and R. pisocarpa. Gametes with eight chromosomes are sometimes produced, but no diploid has been found possessing a reduplicated whole chromosome. 2. A plant of R. pyrifera Rydb. (group of R. woodsii), previously reported to have 2n = 16, has a small unequal pair which are really reduplicated homologous fragments of approximately half a chromosome. They pair with each other and with two different pairs. 3. Both fragments fail to pair in a proportion of cases. The larger, f', consists of two segments, homologous with two different pairs. This reduces its pairing frequency (in agreement with the chiasma theory of chromosome pairing) to less than that of the shorter fragment, f. The plant is 4x for one short segment and 3x for another. This is the only example of fragments yet found in Rosa. 4. Multivalent associations of chromosomes are frequent among tetraploid roses, but are relatively rare in hexaploids and octoploids. 5. Triploids with a high proportion of trivalents at diakinesis and first metaphase have been found in diploid cultures of R. blanda, R. macounii (group of R. woodsii), and R. pisocarpa. These probably originated from unreduced gametes and arose without hybridization. 6. The unbalanced tetraploid R. villosa (section Caninae) shows a high chiasma frequency among 14 chromosomes and a very low frequency among the other 14, which usually occur as univalents. In 75 per cent of the nuclei examined, from one to four of the latter were paired terminally with each other or with one of the regular pairs. Trivalents were found in eight nuclei out of 20. Failure of pairing of the chromosomes is probably due to differential precocity in prophase development, not to hybridization. 7. The chiasma frequency of the fourteen regularly pairing chromosomes in R. villosa is 3.2 chiasmata per bivalent at early diakinesis, and terminalization is almost complete at first metaphase. 8. The types of structural change and the different kinds of polyploids found in Rosa are described. The exceptional types of pairing found are in conformity with the chiasma theory of pairing and are in three instances such as would be predicted on that theory.