On the Cytology of Umbonia crassicornis (Amyot and Serville) (Homoptera: Membracidae: Hoplophorioninae)

Karyotype of the Membracid Umbonia crassicornis is 9 II + XO; 2n = 20 in female, 2n = 19 in male. It is presumably a fusion derivative from the basic Membracid 10 II + XO Accordingly, one of the autosomal pairs of U. crassicornis is notably large. All chromosomes are metacentric; and, except for the X chromosome, euchromatic. In the male, chiasma frequency is only 9.40 per nucleus. Chiasmata are confined to distal halves of the arms. Such a karyotype forms a conservative recombination apparatus that may have helped the species in its rapid adaptation to the Puerto Rican habitat, which presumably does not differ much from the habitat of the mother population.

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POSTREDUCTION OF THE X-CHROMOSOME AND COMPLETE CHIASMA INTERFERENCE IN THE LAMPYRIDAE (COLEOPTERA)

Canadian Journal of Zoology ◽

10.1139/z53-017 ◽

1953 ◽

Vol 31 (3) ◽

pp. 179-192 ◽

Cited By ~ 5

Author(s):

Stanley G. Smith ◽

Doreen E. Maxwell

Keyword(s):

X Chromosome ◽

Chiasma Frequency ◽

Early Prophase ◽

Single Individual ◽

Length Frequency ◽

Autosomal Bivalents ◽

The Family ◽

Frequency Relationship ◽

Five Tribes ◽

Chiasma Interference

Five species representing four genera in three of the five tribes comprising the Lampyridae of North America, the only genera known cytologically, have nine pairs of autosomes and an XX (♂): XO (♀) sex-determining mechanism. A single individual of one species, Pyractomena angulata, carried supernumerary chromosomes, which varied in number in different cells from zero to four. The X-chromosome of males is strongly, positively heteropycnotic during early prophase; the X-bivalent of females is indistinguishable from the autosomal bivalents at pachytene. The complements of the five species are indistinguishable but within the complement there are considerable differences both in size and in the position of the centromeres. In all five species the chiasma frequency per cell is without exception nine: univalents not being encountered, the recombination index for the family, as known cytologically, stands uniformly at 81. Chiasma interference, being complete, must therefore extend across the centromere. The supernumeraries, which approximate one-half the size of the smallest regular autosome, have a chiasma frequency of ca. 0.25 per chromosome, or one-half that of the smallest autosome. They thus demonstrate that, contrary to the evidence provided by the regular complement, a length-frequency relationship exists among the latter but is masked by the totality of chiasma interference. As in other beetles, the centromeres are localized, but the lampyrids are unique in having postreductional division of the X in males. Other insect groups with postreduction have, or are reputed to have, diffuse centromeres: one, the Odonata, is invariably postreductional.

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