The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution

The effects of a complex series of Robertsonian polymorphisms on chiasma frequency and distribution were analysed in natural populations of the grasshopper Dichroplus pratensis which has a standard karyotype of 2n = 19 (XO♂) telocentrics. Populations are usually polymorphic for one to three of seven...

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Autor principal: Bidau, Claudio Juan
Publicado: 1990
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0018067X_v64_n2_p145_Bidau
http://hdl.handle.net/20.500.12110/paper_0018067X_v64_n2_p145_Bidau
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling paper:paper_0018067X_v64_n2_p145_Bidau2023-06-08T14:39:20Z The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution Bidau, Claudio Juan The effects of a complex series of Robertsonian polymorphisms on chiasma frequency and distribution were analysed in natural populations of the grasshopper Dichroplus pratensis which has a standard karyotype of 2n = 19 (XO♂) telocentrics. Populations are usually polymorphic for one to three of seven distinct fusions between the six large (L_a –L_6) autosomes. The study revealed that: 1. Standard males have an essentially proximal-distal pattern of chiasma distribution. Interstitial chiasmata are less frequent. 2. Fused males have significantly fewer total and proximal chiasmata than standards from the same population but show an increase in interstitial and distal chiasmata. 3. The former is due to the fact that centric fusions, either homozygous or heterozygous, produce a decrease in total chiasma frequency of the involved chromosomes and a redistribution of chiasmata resulting in a sharp reduction of proximal chiasmata and an increase in interstitial and distal ones. In this respect, there are no significant differences between fusion trivalents and corresponding fusion bivalents. The same chromosomes in the basic homozygous state, have a typical standard chiasma pattern. 4. The effects of each fusion are intrachromosomal and although the same chiasma repatterning occurs in all seven fusions, total reduction in chiasma frequency depends on the telocentrics involved since a highly significant positive correlation exists between telocentric length and chiasma frequency. Since all chromosome arms tend to have a minimum of one chiasma, the effects of a fusion are more marked in longer autosomes. 5. Comparisons of populations that differ for number and frequency of fusions, showed a highly significant negative correlation between mean number of different fusions per male (per population) (F) and total chiasma frequency per cell (Xta). The same type of correlation exists between F and proximal Xta and F and between-cell variance of total Xta frequency, while a positive correlation was found between F and mean interstitial chiasmata. 6. According to 5, intrachromosomal recombination within populations decreases as number and frequency of fusions increase. This effect is added to the instant reduction of interchromosomal recombination produced by the combination of two linkage groups into one. These results suggest that redistribution of chiasma patterns is due to a direct effect of the rearrangements. Furthermore, the changes in chiasma patterns are discussed in relation to the maintenance of the polymorphisms since trivalents require the elimination of proximal and interstitial chiasmata for balanced orientation and segregation. This was corroborated by the finding of a population in which three fusions were fixed. Here, proximal and interstitial chiasmata in the fused chromosomes are significantly more frequent than expected. Finally, the modifications of recombination potential are discussed relative to the possible adaptive role of these widespread polymorphisms and to a model of chromosomal evolution for the species. © 1990 The Genetical Society of Great Britain. Fil:Bidau, C.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 1990 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0018067X_v64_n2_p145_Bidau http://hdl.handle.net/20.500.12110/paper_0018067X_v64_n2_p145_Bidau
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
description The effects of a complex series of Robertsonian polymorphisms on chiasma frequency and distribution were analysed in natural populations of the grasshopper Dichroplus pratensis which has a standard karyotype of 2n = 19 (XO♂) telocentrics. Populations are usually polymorphic for one to three of seven distinct fusions between the six large (L_a –L_6) autosomes. The study revealed that: 1. Standard males have an essentially proximal-distal pattern of chiasma distribution. Interstitial chiasmata are less frequent. 2. Fused males have significantly fewer total and proximal chiasmata than standards from the same population but show an increase in interstitial and distal chiasmata. 3. The former is due to the fact that centric fusions, either homozygous or heterozygous, produce a decrease in total chiasma frequency of the involved chromosomes and a redistribution of chiasmata resulting in a sharp reduction of proximal chiasmata and an increase in interstitial and distal ones. In this respect, there are no significant differences between fusion trivalents and corresponding fusion bivalents. The same chromosomes in the basic homozygous state, have a typical standard chiasma pattern. 4. The effects of each fusion are intrachromosomal and although the same chiasma repatterning occurs in all seven fusions, total reduction in chiasma frequency depends on the telocentrics involved since a highly significant positive correlation exists between telocentric length and chiasma frequency. Since all chromosome arms tend to have a minimum of one chiasma, the effects of a fusion are more marked in longer autosomes. 5. Comparisons of populations that differ for number and frequency of fusions, showed a highly significant negative correlation between mean number of different fusions per male (per population) (F) and total chiasma frequency per cell (Xta). The same type of correlation exists between F and proximal Xta and F and between-cell variance of total Xta frequency, while a positive correlation was found between F and mean interstitial chiasmata. 6. According to 5, intrachromosomal recombination within populations decreases as number and frequency of fusions increase. This effect is added to the instant reduction of interchromosomal recombination produced by the combination of two linkage groups into one. These results suggest that redistribution of chiasma patterns is due to a direct effect of the rearrangements. Furthermore, the changes in chiasma patterns are discussed in relation to the maintenance of the polymorphisms since trivalents require the elimination of proximal and interstitial chiasmata for balanced orientation and segregation. This was corroborated by the finding of a population in which three fusions were fixed. Here, proximal and interstitial chiasmata in the fused chromosomes are significantly more frequent than expected. Finally, the modifications of recombination potential are discussed relative to the possible adaptive role of these widespread polymorphisms and to a model of chromosomal evolution for the species. © 1990 The Genetical Society of Great Britain.
author Bidau, Claudio Juan
spellingShingle Bidau, Claudio Juan
The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
author_facet Bidau, Claudio Juan
author_sort Bidau, Claudio Juan
title The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
title_short The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
title_full The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
title_fullStr The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
title_full_unstemmed The complex robertsonian system of dichroplus pratensis (Melanoplinae, acrididae). II. effects of the fusion polymorphisms on chiasma frequency and distribution
title_sort complex robertsonian system of dichroplus pratensis (melanoplinae, acrididae). ii. effects of the fusion polymorphisms on chiasma frequency and distribution
publishDate 1990
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0018067X_v64_n2_p145_Bidau
http://hdl.handle.net/20.500.12110/paper_0018067X_v64_n2_p145_Bidau
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