Metaphase I orientation of Robertsonian trivalents in the water-hyacinth Cornops aquaticum (Acrididae: Orthoptera).

COLOMBO, P.C.

GENETICS AND MOLECULAR BIOLOGY

Sociedade Brasileira de Genetica.

Lugar: Ribeirao Preto, SP, Brasil.; Año: 2009 vol. 32 p. 91 - 95

1415-4757

Trivalents resulting from polymorphic Robertsonian rearrangements must have a regular orientation if the polymorphisms are to be maintained. It has been argued that redistribution of proximal and interstitial chiasmata to more distal positions is necessary for a convergent orientation, the only one that produces viable gametes. Cornops aquaticum is a South-American grasshopper that lives and feed on water-hyacinths, and has three polymorphic Robertsonian rearrangements in its southernmost distribution area in Central Argentina and Uruguay. The orientation of trivalents in metaphase I, the formation of abnormal spermatids and the frequency and position of chiasmata in the trivalents was analysed in a polymorphic population of C. aquaticum. In this study we observed a correlation between the number of trivalents with the frequency of abnormal spermatids; additionally, the number of chiasmata, especially proximal and interstitial ones, was strongly correlated with the with the frequency of the linear orientation. Therefore we confirmed our previous assumption, based on other evidence, that chiasma redistribution in fusion carriers is essential to the maintenance of the polymorphism