Recent advances in cytology

A comparative cytological and morphological study of mesostoma ehrenbergii ehrenbergii and mesostoma ehrenbergii wardii

Cytological Studies in Some Species of Panicum

Chiasma frequency and position are good estimators of genetic recombination in a population. Darlington proposed a recombination index that consisted of the sum of the haploid number (n) and the average chiasma number per nucleus (x); this index (n+x) represents the average number of elements that segregate independently, so that the number of possible gametes equals 2(n+x). Here a more accurate approach is intended by proposing an index that takes into account: (a) the proportional length of chromosomes and (b) the accurate position of chiasmata. The development of simulation programs and the study of real cases (v.gr. Leptysma argentina) demonstrated that the index of Darlington (a special case of Ir and I′r) is always an overestimation of the recombination level of a population. Hence indexes Ir and I′r are proposed for organisms that allow a reasonably accurate measurement of chiasma distribution.

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A new index for estimating genetic recombination from chiasma distribution data

Mechanisms of two F1 hybrids (D46A × DTP-4 and D46A × Dminghui63) of autotetraploid rice (2n = 4x = 48) showing extremely high pollen fertility 87.40% and 85.97%, respectively, seed set 82.00% and 79.00%, respectively and extremely high level of heterosis were analyzed cytologically. The chromosome pairing of D46A × DTP-4 and D46A × Dminghui63 was normal at metaphase I(MI), and had almost no I or III, with an average of 0.020I +14.36 II 6.44rod+7.91ring) +0.01III + 4.80 IV + 0.01VIII and 0.06 I + 17.67 II (11.01rod + 6.67ring)] + 0.06 III +3.10IV+0.01VI, respectively. The most frequent chromosome configurations were 10II+7IV and 12II+bIV. The bivalent frequency was less frequent in hybrids than that in restoring parents, and the same results were gained from univalents, trivalent and multivalents. However, the quadrivalent frequency was significantly higher in hybrids than that in restoring parents at MI. The other meiotic phases progressed normally, except for low percentages of PMCs with lagging chromosomes at AI and low percentages of PMCs with micronuclei at telophaseI (TI) and telophaseII (TII). PMCs with lagging chromosomes at AI and PMCs with micronuclei at TI and TII showed negative correlation between pollen fertility and seed set. Above 90% of the PMCs could form normal microspores, which resulted in the production of viable pollen grains, abnormal microspores were observed including penta-fission and hexa-fission. Based on these results we suggest that the two F1 hybrids had better behaviors of chromosome pairing and genetic stability than autotetraploid rice and other autotetraploid plants ever studied.

Recent advances in cytology

Citations

A comparative cytological and morphological study of mesostoma ehrenbergii ehrenbergii and mesostoma ehrenbergii wardii

Cytological Studies in Some Species of Panicum

A new index for estimating genetic recombination from chiasma distribution data

Cytogenetic studies on two F1 hybrids of autotetraploid rice varieties showing extremely high level of heterosis

Cytotaxonomy of Commelinaceae: chromosome numbers of some African and Asiatic species

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