PubMed Health⌕ Search

Biomedical subjects

R N Nankivell

Publications and source records attributed to R N Nankivell.

3 recordsLinked to original sources
PubMed1976

Karyotype differences in the crenaticeps-group of Atractomorpha (Orthoptera, Acridoidea, Pyrgomorphidae).

The four known species of the crenaticeps-group of the genus Atractomorpha have 2n (male)=18+X0. All members of the complement are rod-chromosomes and the smallest autosome (no. 9) is megameric. The four species have similar amounts of euchromatin but differ markedly in the amount of heterochromatin present in their genomes. In A. similis, A. crenaticeps and the unnamed species, "Species-1", there are distinct proximal segments of heterochromatin in the eight large autosomes. In A. similis these chromosomes also have prominent distal segments of heterochromatin. The fourth species, A. australis, has no visible heterochromatin in its eight large autosomes except for a small segment at the proximal end of autosome 4. In all four species, the heterochromatic segments influence chiasma frequency and chiasma position. Moreover the overall chiasma frequency is lowest in A. similis with most heterochromatin and highest in A. australis with least heterochromatin.

Animals↗
PubMed1976

Telomeric satellite DNA functions in regulating recombination.

Molecular and cytogenetical analyses of three sibling species of Australian grasshopper, Atractomorpha australis, A. species-1 and A. similis, resolves one of the long standing problems of highly repeated DNA. In this system satellite DNA functions in regulating the level and position of recombination, irrespective of whether the repeated DNA is located in telomeric or centric regions. Even though the three species do not differ in their euchromatic genome sizes, their relative DNA contents are 1.00/1.10/1.41, the difference in genome size being due solely to visible centric or telomeric blocks of heterochromatin. Antibiotic analytical and preparative ultracentrifugation, in situ hybridization and renaturation kinetic analyses reveal that a large cryptic satellite of A. similis constitutes the heterochromatic telomeric blocks of nearly all autosomes and that the DNA of this satellite is highly repeated. Comparison of these grasshopper data with published literature of heterochromatic rearrangements in Drosophila and with heterochromatin distribution and recombination patterns in diploid plant species reveals that in every case heterochromatin is implicated in some form of alteration in the meiotic recombination system.

Animals↗