Genotype-dependent effect of B-chromosomes on chiasma frequency in Eyprepocnemis plorans (Acrididae: Orthoptera)

In order to analyze the effect of B-chromosomes on chiasma frequency, the offspring of different females of the grasshopper Eyprepocnemis plorans have been studied. From the comparison between individuals of the different families having a given number of B's and between individuals with different numbers of B-chromosomes within the same family, it can be concluded that the effect of the genetic background on chiasma frequency is greater than that produced by the presence of B's, and that there is a between-families variation in the effect of B-chromosomes which, in addition, is negatively correlated with the chiasma frequency of related individuals without B's. This genotype-dependent effect of B-chromosomes is discussed.     

The relation between pairing preference and chiasma frequency in tetrasomics of rye.

The association pattern of marked tetrasomes of Secale chromosome 1R at meiotic first metaphase was analyzed. Two of the four chromosomes were identical with terminal C-bands at both arms; the other two were also identical but lacked C-bands and were homologous or homeologous with the first two. Four different types of heterozygotes for 1R were studied: (i). autotetraploid hybrids between genetic variants within Secale cereale subsp. cereale, (ii). tetraploid hybrids between subspecies of Secale cereale, (iii). tetraploid hybrids between species of Secale, and (iv). autotetrasomes of S. cereale in a wheat background. Earlier observations that heterozygous associations (banded with unbanded) had consistently higher chiasma frequencies than homozygous associations were extended and confirmed. To analyze this phenomenon more closely, the possible relations between this correlation and several other meiotic phenomena were studied. For this analysis, three genetically different autotetraploid hybrids within S. cereale were selected that differed with respect to the relation between pairing type and chiasma frequency. Special attention was given to different patterns of interference and other meiotic phenomena in the two chromosome arms of chromosome 1R. No relations between such phenomena and the relation between pairing type and chiasma frequency could be established. A hypothesis is formulated assuming that long-distance homologue attraction is concentrated in a limited number of sites and that in different genotypes, different patterns of active sites are present. Moderately weak attraction sites can pair with strong homologous sites under favorable genetic conditions, but two weak sites cannot. Then, heterozygotes have more effective pairing initiation and consequently chiasma formation than homozygotes. Under less favorable conditions, only strong sites are effective, and then, homozygotes pair better, but the chiasma frequency is lower. A model of the forces involved in homologue attraction is presented.     

The effect of Actinomycin-D on chiasma frequency in Vicia faba

The effect of Actinomycin-D was studied on chiasma frequency in Vicia faba (var. Weibull's Akerabona). A significant decrease in chiasma frequency over control was observed in all cases irrespective of the time of fixation and chemical concentration. However, the maximum decrease was found in the material fixed after a recovery period of 24 hours. The decrease in chiasma frequency showed a linear relationship with time of recovery. Besides reduction in the chiasma frequency, cells showing complete failure of homologous pairing were also observed. These findings are discussed in the light of actinomycin-D action.     

Interchromosome effects on chiasma frequencies in rye

In interchange heterozygotes and interchange trisomics of rye (Secale cereale) correlations between multivalents and bivalents in respect of number of chromosome arm pairs bound at MI, were studied. No significant positive correlations were observed. Significant negative correlations, indicating interchromosome effects, were found only in cell populations that approached anaphase. The effects seem to be generated by non-random loss of chiasmata from chromosome ends. The absence of demonstrable real interchromosome effects on chiasma formation in the material studied may be explained by positive correlations (due to between-cells variation) counteracting possible negative correlations. Another explanation may be found in the fact that intra-chromosome interference, that might be one of the ways through which interchromosome effects act, does not come to expression with the methods of observations used.     

B chromosome frequency in yugoslav rye populations

Cytologická analysa 25 populací ?ita z Jugoslavie, které byly vybrány ve Slovinsku, Srbsku a Makedonii, ukázala, ?e ve v?ech analysovaných populacích (100 %) se vyskytovaly B-chromosomy. Po?et p?ítomných B-chromosom? byl nízký, od 1 do 3, p?i ?em? pr?mě rný po?et na jednu rostlinu se pohyboval v rozmezí od 0,13 do 0,97. Pr?měrná ?etnost ?itných rostlin s B-chromosomy byla pro Jugoslavii 27, 10%. ?etnost rostlin s B-chromosomy a pr?měrný po?et chromosom? této kategorie, vzta?ený na jednu rostlinu, byly zna?ně vět?í v aridní oblasti Makedonie ne? v humidní oblasti Slovinska. Rozdíly byly reálné a významné, jak to bylo proká záno biometricky. P?i hodnocení údaj? jiných autor? o populacíoh primitivních asijských ?it bylo zji?těno, ?e frekvence B-chromosom? je ni??í v populacích z oblastí, ozna?ovanýeh jako centra p?vodu tohoto rostlinného druhu (Blízký Východ, Malá Asie) a postupně se jejich frekvence zna?ně zvy?uje s postupem ve směru na vychod (Zabajkali, Korea) i ve směru na západ (Balkánský poloostrov, Jugoslavie). Diskutují se mo?né p?í?iny zvy?ování ?etnosti B-chromosom? v populacich vně center p?vodu ?ita a je zd?razněn význam jejich studia v západoevropských populaeí eh primitivních forem ?ita.     

Relationships between frequency,localization and errors in chiasma formation in desynaptic rye

Four inbred lines of rye (Secale cereale) and the F₁ and F₂ from the cross between two of them have been studied. The results indicate that the genotypes used show variation in chiasma frequency, chiasma error frequency and chiasma localization. Significant correlations between these characters have been found: as chiasma frequency decreases both chiasma error frequency and distal localization increase. These correlations lead us to the assumption that these anomalies are in fact secondary effects of the failure of some preconditions for exchange. It is suggested that one such exchange precondition may be effective pairing.     

An effect of potassium on chiasma frequency and recombination

High and low concentrations of potassium and calcium were combined factorially and applied to the plant,Lolium temulentum. An effect on mean plant chiasma frequency was detected when such plants underwent meiosis at 30°C. Potassium rather than calcium was shown to be the mineral responsible for the observed effects. High concentration of potassium resulted in an increase in mean chiasma frequency. At 20°C little effect of either mineral could be demonstrated, although potassium again was responsible for most of the variation produced.Potassium has also an effect on stability. At 30°C high concentrations of potassium reduce plant variation, whereas at 20°C the converse occurs and an increase in plant variation results. It is suggested that such a difference between the two temperatures supports the conclusion that different genetic systems control the plant means and plant variation.The effect of potassium on chiasma frequency was confirmed inDrosophila melanogaster by studying its effects on recombination in the X chromosome. A striking influence on body size, possibly correlated with recombination, was also observed.The conflict of such results with previous work in which calcium has been shown to be the most important mineral is discussed. The difficulties of arguing a direct role at meiosis for external treatments is emphasised.     

On the influence of decreased chiasma frequency on preferential MI pairing behaviour of rye chromosomes in wheat-rye derivatives

Meiotic behaviour of identical and homologous rye chromosomes was investigated in colchicine-induced duplicated meiocytes obtained from different wheat-rye derivatives. A great reduction in the amount of metaphase I (MI) associations accompanied by a strong tendency for identical over homologous nonidentical preferential MI pairing was found in all of the four rye chromosome arms analysed. Both of these features appear to be associated with a more distal chiasma localization where the presence of an interstitial C-band has allowed two distinct regions within the same chromosome arm to be studied separately. On the other hand, the MI pairing failure observed for the rye chromosomes under analysis does not seem to be an effect of telomeric or interstitial C-heterochromatin.by P.B. Moens     

B-chromosomes in inbred lines of rye (Secale cereale L.)

B chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment is a way of studying the effects of the Bs against a range of different homozygous A chromosome backgrounds. This publication deals with pairing effects of both the As and the Bs, and their interactions, and with pollen mitosis. At meiosis there is a genotypic component to B effects, and they do not appear to act solely through a physical disturbance within the nucleus. In pollen the Bs are always present in more than 50% of the grains regardless of their pairing behaviour during meiosis; this result fits with a parasitic model of the activity of rye Bs.     

B-chromosomes in inbred lines of rye (Secale cereale L.)

B-chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment provides a way to study the effects of the Bs against a range of homozygous A-chromosome backgrounds. This publication deals with vigour and fertility: it shows that the rye Bs fit a parasitic model, and that they interact in their effects with the A-chromosome background genotype.     

A re-examination of chiasma terminalization and chiasma frequency in male mice

The distribution and frequency of chiasmata have been analyzed in male BALB/c mice. Bivalents were classified in terms of the number of interstitial chiasmata (CH) and terminal associations (TA) present as follows; 1CH, 2CH, 1TA, 2TA, 1CH·1TA, 1CH·2TA, 2CH·1TA, 2CH-2TA and 0. We provide evidence that the TA frequently dissociates during 1st meiotic prophase. Consequently six of the observed bivalents may be derived from three basic bivalent types (namely 2CH·2TA, 1CH·2TA and 2TA) by dissociation of the TA according to the following schemas: (1) 2CH·2TA2CH·1TA2CH, (2) 1CH·2TA1CH·1TA1CH, and (3) 2TA1TA0. We also provide evidence that interstitial chiasmata do not move, which implies that a TA can not be formed by chiasma terminalization. The chiasma frequency estimated by assuming that terminal associations do not result from terminalized chiasmata is 17.2±2.4 compared to a value of 25.4±2.2 calculated on the assumption of chiasma terminalization.