R. Giraldez

Chromosome C-banding patterns in Spanish Acridoidea

The karyotypes of 47 Spanish acridold grasshoppers have been analyzed by means of C-banding in both mitotic and meiotic cells. The most frequent location of C-heterochromatin occurs in centromeric and telomeric regions whereas interstitial C-bands are very scarce. No clear relationship between similarities in C-banding patterns and taxonomic proximity has been found. Negatively heteropycnotic regions are described; their uniform location and distribution suggest that they could represent a functional chromosome structure as nucleolar organizers.

The effect of C-heterochromatin in chiasma terminalisation in Chorthippus biguttulus L. (Acrididae, Orthoptera)

Using the Giemsa C-banding procedure, a polymorphism in chromosome banding pattern has been found in a spanish population of Chorthippus biguttulus. The variation in C-banding pattern shown by bivalent M 6 allowed to study the effect of C-heterochromatin on chiasma terminalisation. The results indicate that interstitial heterochromatin acts as a barrier preventing chiasmata to pass. Anaphase separation seems to be normal but could be slightly delayed. A similar role for telomeric C-heterochromatin is suggested.

Chiasma interference and centromere co-orientation in a spontaneous translocation heterozygote of Euchorthippus pulvinatus gallicus (Acrididae; Orthoptera)

The meiosis of an individual of the species Euchorthippus pulvinatus gallicus heterozygous for a reciprocal translocation involving chromosomes 3 and 6 has been analysed using the Giemsa C-banding technique. It is concluded that: (i) Chiasma interference in the quadrivalent seems to act only at the arm level. There is no interference across the translocation break point. No interchromosomal chiasma interference could be demonstrated, (ii) The results concerning the co-orientation of the quadrivalent suggest that the length of the chromosomal segments between two adjacent centromeres at metaphase I is related with their orientation behaviour.

Metaphase I bonds, crossing-over frequency, and genetic length of specific chromosome arms of rye

Using a Giemsa C-banding procedure three chromosome pairs (3, 6 and 7) have been identified in meiosis of the F1 of a cross between two rye inbred lines. Two of these chromosome pairs (3 and 7) were heterozygous for a prominent telomeric heterochromatic band. The comparison between the frequencies of the different meiotic configurations at metaphase I, anaphase I and metaphase II presented by these two chromosome pairs has allowed the estimation of the chiasma frequency and the genetic length of the chromosome arms 3 short and 7 long.

C-heterochromatin polymorphism and variation in chiasma localization in Euchorthippus pulvinatus gallicus (Acrididae, Orthoptera)

Eight populations of the grasshopper Euchorthippus pulvinatus gallicus have been analyzed by means of C-banding. Chromosome pairs M6, M7 and S8 show both quantitative and qualitative variation in their C-heterochromatin. There are at least four different types of M6, three of M7 and two of S8. Differences in the frequencies of these chromosome types have been found between populations. Within a given population the frequencies of the different M7 and S8 chromosomes fit a Hardy-Weinberg distribution and they remain constant within and between generations. The possible adaptative role of supernumerary heterochromatin as leading to a redistribution of chiasmata in the heterochromatin carrier chromosomes is discussed.

B-chromosome polymorphism and interchromosomal chiasma interference in Eyprepocnemis plorans (Acrididae; Orthoptera)

Using the C-banding technique, the morphology and meiotic behaviour of four different types of B-chromosomes present in several populations of Eyprepocnemis plorans have been studied. The possible relationship between these four types is discussed. The analysis of chiasma frequency in A and B-chromosomes suggests the existence of interchromosomal interference and demonstrates that the chiasma frequency of B-s depends on the genetic background of the individual carrying them.

Cytological evidence for preferences of identical over homologous but not-identical meiotic pairing.

A spontaneous tetraploid/diploid chimera involving meiotic cells of a male individual of Euchorthippus pulvinatus gallicus was heterozygous for the C-banding pattern in chromosome pair 8. This allowed the study of the possible existence of competition in meiotic pairing between identical and homologous but not-identical chromosomes. The results suggest the existence of such a competition. An excess of bivalents formed by identical chromosomes was observed. It is suggested that during the pairing process slight specificity or activity differences between chromosomes with a high degree of resemblance would be responsible for the pairing preferences found.

Metaphase I bound arms and crossing over frequency in rye

Using a Giemsa C-banding procedure it has been possible to identify at meiosis three chromosome pairs of a local Spanish rye cultivar. Two of these chromosomes (3 and 5) were heterozygous for an interstitial C-band in the long arm and the other (chromosome 7) was heterozygous for a telomeric C-band, also in the long arm. From the frequency of being bound at metaphase I and the frequency of recombined chromatids at anaphase I in the arms considered, estimates of actual chiasma frequencies have been derived. The results have been compared with those obtained in a Fl between two inbred lines. It is concluded that: (i) Although the frequency of bound arms analyzed was similar in all cases, the chiasma frequency was higher in the cultivar than in the Fl plants. Cultivar plants showed a variation in chiasma frequency for the bivalent arms studied which was correlated with the frequency of bound arms per cell, indicating that the estimation for chiasma frequency by means of bound arm frequency has an error that increases with increasing number of bound arms per cell, (ii) Evidence of chiasma terminalization has not been found, (iii) It is suggested that the different rye chromosomes have different chiasma localization patterns, which, in turn, are related with the chiasma frequency.

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.

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 Bs 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 Bs, 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 Bs. This genotype-dependent effect of B-chromosomes is discussed.