CARYOTYPES, CHROMOSOMES SURNUMERAIRES, PARTHENOGENESE RUDIMENTAIRE ET POLYPLOIDIE CHEZ DEUX ESPECES DU GENRE PHRONIMA (CRUSTACES, AMPHIPODES)

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Abstract
The diploid number of Phronima sedentaria and P. atlantica is 30, all the chromosomes are metacentric or submetacentric; the caryotypes of these two species are compared with those of other Amphipods. Some individuals of each species have a supernumerary chromosome. This element, found in both sexes, remains as an univalent at meiosis and goes earlier to one pole. In some cases nonfertilized ova undergo segmentation; this rudimentary parthenogenesis stops quickly and is partly related to polyploidization.
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