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Biomedical subjects

P G Fontana

Publications and source records attributed to P G Fontana.

6 recordsLinked to original sources
PubMed1976

Improved resolution of the meiotic chromsomes in both sexes of Euxoa species and their hybrids (Lepidoptera: noctuidae).

An air drying and Giemsa staining technique produces consistently good quality cytological preparations when applied to different species of Euxoa (Lepidoptera: Noctuidae) and, in particular, it allows an imporved resolution of the meiotic chromosomes in both sexes. All species so far investigated have a basic haploid chromosome complement of n (male) = 31(XX): n(female) = (XY). A single chiasma per individual bivalent is clearly visible in the male sex. Some chiasmata are formed in interstitial positions, but, by metaphase I, they have all undergone complete terminalization while the bivalents orient axially on the first division spindle. Direct evidence for lack of chiasma formation in the 31 hormorphic bivalents in the female sex is reported for the first time for species of Noctuidae. Evidence in favor of an XY system in the female sex is discussed. Preliminary studies of the meiotic divisions in hybrid material reveal the presence of cryptic structural differences between certain taxa, and will help to elucidate taxonomic problems within this complex genus.

Animals↗
PubMed1975

The B-chromosome system of Tettigidea lateralis (Say). II. New karyomorphs, patterns of pycnosity and giemsa-banding.

Additional samples from a discrete population of the pygmy grasshopper Tettigidea lateralis, at the periphery of the species range, have shown that the frequency of the B-chromosomes has remained stable over a two year period (30-35%), and that there is not significant difference for this metric in the two sexes. The intensity of the preferential movement of the B with the X at male first meiotic division has also remained constant in time and homogenous in different individuals. Hence it is possible that this distortional effect plays a role in the equilibrium frequency of the B in the population. The B's may possess special adaptive properties under ecologically marginal conditions, since in a number of more 'central' demes they occur at much lowere frequencies (7-9%). -Unique morphological and/or behavioral variants of the standard B were encountered in addition to distinct cases of spontaneous fragmentation of A elements. The meiotic behavior and chromatic expression of these centric fragments provide evidence on the possible origin and evolution of supernumeraries. A modified. Giemsa staining technique has been used to identify regions of centromeric (C-) hererochromatin in mitotic and meiotic chromosomes. The C-banding pattern of the X and the allocyclically similar B is compared. It suggested that the B may have originated from the X by deletion of centromeric heterochromatin. This may have affected the centromere "strength" of the nascent B leading to its preferential movement with the X at anaphase I.

Adaptation, Biological↗