The B-chromosomes of two species ofCylindrotettix (Leptysminae,Acrididae) |
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Authors: | V A Confalonieri C J Bidau |
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Institution: | (1) Laboratorio de Genética, Depto Ciencias Biológicas, Fac. Cs Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, 1428 Buenos Aires, Argentina;(2) Becaria Conicet, Argentina |
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Abstract: | Twenty-four males ofCylindrotettix obscurus and ten ofC. santarosae (Leptysminae, Acrididae) from Rio Claro, Brazil, were cytologically analysed. Both species are 2n = 23 ♂ (22+XO), all chromosomes
being telocentric except for 4 acrocentric pairs ofC. obscurus. Two different B-chromosomes were found inC. obscurus: (1) a small, mitotically unstable telocentric (BT) and (2) a medium-sized, mitotically stable submetacentric (B1). B1 has a large pericentromeric heterochromatic portion and two distal euchromatic segments where both terminal associations
and interstitial chiasmata are regularly formed producing a ring univalent at prophase I. B1 is almost certainly an iso-chromosome which has undergone a centromeric shift through pericentric inversion or centric transposition
(heterochromatin duplication or deletion could also be the cause of arm inequality). InC. santarosae, a single male carried a small mitotically stable telocentric B-chromosome.
Both B types ofC. obscurus significantly increased the production of abnormal sperm (diploid, tetraploid and micro-spermatids) when compared to 0B individuals
although their effects were differential: BT induced higher frequencies of microspermatids especially in those follicles with odd BT numbers, while in B1 carriers the increase was chiefly due to polyploid spermatids. None of the Bs ofC. obscurus affected cell mean chiasma frequency nor the between-cell variance. The B ofC. santarosae had no effect on abnormal sperm production but it probably increased cell mean chiasma frequency. |
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