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Abstract: Let? C be the regularity of the Hilbert function of a projective curveC inP K n over an algebraically closed fieldK andß 1,...,ß n-1 be degrees for which there exists a complete intersection of type (ß 1,...,ß n-1) containing properlyC. Then the Castelnuovo-Mumford regularity ofC is bounded above by max {? C + 1,ß 1 +...+ß n-1-(n-1)}. We investigate the sharpness of the above bound, which is achieved by curves algebraically linked to ones having degenerate general hyperplane section.

AbstractGenotoxic effect as tested of chronic exposure to three different concentrations of Chromium (III) on polytene chromosomes of larvae of Chironomus riparius(syn. Chironomus thummi) from the embryonic stage to the IV larval instar for two successive generations. In chromosomes AB, CD, EF and G significant differences of chromosome aberrations were found between exposed and control larvae as well as changes in functional activity (induction of novel puffs not corresponding to those induced during normal larval development in arms A, B, C and E, telomeric and centromeric decondensations especially at telomeres of chromosome G and arm C.). No significant differences were found between the effects of the three treatments nor between the two generations. In chromosome G the Balbiani Ring system (where some permanently active regions are involved in transcription of salivary proteins) appeared as a model for studying the response of the genome to Cr (III) treatment. In approximately one-third of the cells of the exposed larvae, the activity of the Balbiani rings BRc and BRb was reversed. In 10% of the cells of both generations of treated larvae, deletion or collapse of BRc was observed. Pomponlike G chromosomes were present in 6% of the cells. This type of chromoosme appeared either in a very decondesed or in a highly condensed state. In 5 % of the treated larvae the apical region of the chromosome G folded back so that the nucleolar organizer region appeared as if it was at the end of the chromosome. These structural and functional chromosomal changes are interpreted as a reaction of the genome to stressful rearing conditions.

AbstractVariation in DNA content was densitometrically analyzed in three sections (E; A4f-g; E; A5d-g; F; B3h) of the chromosome EF of IV instar larvae of Chironomus riparius(syn: C. thummi) Meigen 1804 from a heavy metal polluted Piedmont station (Santena, near Turin). The three sections are known to be composed by AT rich repetitive DNA. Preparations of salivary gland polytenic chromosomes were Feulgen stained and densitometric analysis of digital images of the three sections was performed. DNA density values of each of the three sections fell into several Poisson distributed classes. To explain variation of repetitive DNA content in the three regions, two hypotheses have been considered: during embryonic development, prior to the polytenization process, either somatic mispairing could have occurred with subsequent unequal chromatid exchanges or saltatory replication with subsequent increase of DNA content after breakage of a chromatid. Results support the hypothesis of unequal chromatid exchange as the cause of repetitive DNA size variation.

Differences in karyotypic structure are compared with reported isozyme differences in three Mediterranean species of Patella. In addition, the karyotypic structure of Patella is discussed in terms of the karyotypic variability of Archaeogastropoda. Both P. lusitanica and P. caerulea have a haploid complement of n=9 (6 metacentric, 1 submetacentric, 1 subtelocentric, 1 telocentric chromosome in P. lusitanica and 6 metacentric, 1 submetacentric, 2 telocentric chromosome in P. caerulea). P. aspera, although regarded as morphologically more closely related to P. caerulea, has a haploid complement of only n=8 (7 metacentric and 1 submetacentric chromosomes).