Maria Luiza Beçak

Cytological evidence of constant tetraploidy in the bisexual South American frog Odontophrynus americanus

Odontophrynus americanus has 2n=44 chromosomes in somatic and gonad cells which can be ordered in 11 groups of homologues. In spermatocytes I they form mostly ring quadrivalents. In metaphase II 22 dyads are present. There is no indication of abnormalities in ♂ and ♀ gonad development.

CLOSE KARYOLOGICAL KINSHIP BETWEEN THE REPTILIAN SUBORDER SERPENTES AND THE CLASS AVES.

SummaryIn contrast to the situation found in two classes of warm-blooded vertebrates, mammals and birds, the class Reptilia is not uniform with regard to total genetic content; rather, it contains two distinct categories. The close cytological kinship between snakes and birds was revealed. Both are almost identical in total genetic content, which is about 50 per cent that of placental mammals. Both have microchromosomes, as well as Z-chromosomes very similar in absolute size, comprising nearly 10 per cent of the homogametic haploid (AZ) set. This leads to the implication that snakes and birds originated from the same lineage, and that their Z-chromosomes have not changed substantially since the Jurassic period of the Mesozoic era, about 180 million years ago.Within the reptilian suborder Serpentes, the step-by-step differentiation from the primitive ZW pair to the grossly heteromorphic ZW pair could be observed. In the ancient family Boidae, the sex chromosomes were still homomorphic to each other. In the family Colubridae, the beginning of heteromorphism was manifested in two ways. In some species, a pericentric inversion on the W caused it to differ from the Z; in others, duplication of the W occurred. In the family Crotalidae, the W had apparently achieved its very specialized status; it was a distinctly smaller element.

Cytotaxonomy and chromosomal evolution in Serpentes

The karyotypes of 15 species of snakes are described: Lachesis muta noctivaga , Micrurus lemniscatus carvalhoi , Philodryas aestivus aestivus , &l

Polyploidy and mechanisms of karyotypic diversification in Amphibia

Polyploid species were described in amphibians of the family Ceratophrydidae (Procoela). Tetraploid (4N = 44) and octoploid (8N = 104) karyotypes resulted apparently by duplication of ancestral genome

Evolution by polyploidy in Amphibia: new insights

Polyploidy is an important mechanism of evolution in lower vertebrates, resulting in gene duplication and loci duplication evolving to diploidization. In polyploid anurans DNA is increased, but RNA and protein synthesis is kept at the same levels as in their diploid counterparts. Recent cytogenetic findings in Odontophrynus americanus show: (1) amphiplasty and asynchrony of the cell division cycle in 4n and (2) intra- and interindividual alterations of chromosome 4 morphology in 4n and 2n through breaks at secondary constrictions and at/or around the centromeres, followed by the appearance of changes of centromeres position, dicentrics, bisatellited chromosomes, precocious sister-chromatid segregation, and loss or unequal segregation of the chromosomes. This genome instability suggests the presence of chromosomal aberrations with chromodomain alterations at the centromeres affecting the mechanisms ensuring normal segregation of the chromatids in anaphase of mitosis and meiosis. Cell division asynchrony and chromosome abnormalities, novel findings in polyploids, are discussed respectively in function of gene activity and putative translocations producing polymorphisms in nucleolus organizers and secondary constrictions.

Coturnix coturnix japonica

The materials for the karyograms were prepared from feather pulp and embryonic tissue of coturnix quail secured through the courtesy of Dr. Hans Abplanalp, University of California, Davis. This colony originated from Japan. This species is one of the few among the birds so far described that have metacentric or submetacentric chromosomes recognizable to about chromosome size twenty.

Further studies on polyploid amphibians (Ceratophrydidae)

Meiosis and sex-ratio of artificial interspecific triploid hybrids (3n=33) produced by mating of Odontophrynus cultripes males (2n=22) with O.americanus females (4n=44) are described. — Metaphases I from the triploids show pairing of homologues in configurations of trivalents, bivalents and univalents. Metaphases II revealed a variation of chromosome numbers in the range of 11 to 22. Buploid gametes with 11, 22 and 33 dyads were also found. The latter (3n) arose by pre-meiotic duplication of the chromosomes and/or by absence of meiotic reduction. — Sex-ratio of 1∶1 males to females in one sample of the triploid interspecific hybrids was obtained.

A diploid population of the polyploid amphibianOdontophrynus americanus and an artificial intraspecific triploid hybrid

La ocurrencia de poliploidia ha sido relatada en anuros de la familia Ceratophrydidae incluyendo la especie tetraploideO. americanus (4n=44). En una área geográfica distinta, sin embargo, fue observada una población diploide deO. americanus (2n=22). Fueron obtenidos híbridos intraespecíficos triploides (3n=33) por cruzamiento de ejemplares diploides y tetraploides deO. americanus.

Karyotypic Studies of two Species of South American Snakes (Boa constrictor amarali and Bothrops jararaca)

Karyotypic studies have been made of two species of South American snakes, Boa constrictor amarali and Bothrops jararaca . Both have 36 chromosomes; 16 macrochromo

Diploidization inEleutherodactylus (Leptodactylidae-amphibia)

El contenido de DNA deE. binotatus (2n=22) es cerca de cuatro veces mayor que el deE. guentheri (2n=22) yE. parvus (2n=22). Ese aumento drástico podría ser resultado de duplicationes intersticiales y/o poliploidía, con translocaciones múltiples.