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Biomedical subjects

T Lamb

Publications and source records attributed to T Lamb.

28 records · Page 2Linked to original sources
PubMed1991

Genetic damage in a population of slider turtles (Trachemys scripta) inhabiting a radioactive reservoir.

Turtles inhabiting a radioactive reservoir appear to experience genetic damage due to environmental exposure to low concentrations of long-lived radionuclides. Total body burdens for the 50 reservoir turtles examined in the survey ranged from 164.7-4679.3 Bq for cesium-137 and from 462.6-5098.3 Bq for strontium-90. Flow cytometric (FCM) assays of red blood cell nuclei demonstrated significantly greater variation in DNA content for the reservoir turtles than for turtles from a nearby, non-radioactive site. Furthermore, two of the reservoir turtles possessed FCM profiles that are indicative of aneuploid mosaicism. These data strongly suggest that exposure to low-level radiation may involve a sensitive genetic response in a natural population.

Animals↗
PubMed1991

The role of steroids in reproduction in female elasmobranchs and reptiles.

Adequate evidence exists to suggest the importance of temporal changes in steroid hormone ratios in the normal reproductive/vitellogenin cycle in oviparous and viviparous elasmobranchs and reptiles. In oviparous species, where the cycle is relatively short, secretion of gonadal hormones is synchronous; thus inhibitory actions of progesterone (P) on hepatic or reproductive tract functions would be offset by stimulatory actions of estradiol (E), resulting in appropriate vitellogenin secretion and reproductive tract development. In viviparous species, temporal asynchrony of E and P secretion occurs, and the actions of the individual hormones can be more easily dissected out. Thus, during gestation, where P is the dominant hormone, antagonistic or stimulatory actions of E may be prevented, and the inhibitory action of P on vitellogenesis dominant. Hence vitellogenesis is limited to the follicular phase and eggs are retained. Although the elasmobranch and reptilian species discussed here do not form a continuum through phylogenesis, but rather are extant forms of a particular line of evolution, it is possible to extrapolate from these observations to the probable endocrine interactions in a species as viviparity evolves from oviparity. The theoretical intermediate stage would involve; (a) egg retention, (b) extension of the luteal phase and increased P secretion and (c) resulting in E/P asynchrony and potential expression of "independent" P action, egg retention and yolk suppression.

Animals↗
PubMed1989

DNA fingerprints from hypervariable mitochondrial genotypes.

Conventional surveys of restriction-fragment polymorphisms in mitochondrial DNA of menhaden fish (Brevoortia tyrannus/patronus complex) and chuckwalla lizards (Sauromalus obesus) revealed exceptionally high levels of genetic variation, attributable to differences in mtDNA size as well as in restriction sites. The observed probabilities that any two randomly drawn individuals differed detectably in mtDNA genotype were 0.998 and 0.983 in the two species, respectively. Thus, the variable gel profiles provided unique mtDNA "fingerprints" for most conspecific animals assayed. mtDNA fingerprints differ from nuclear DNA fingerprints in several empirical respects and should find special application in the genetic assessment of maternity.

Animals↗
PubMed1986

Directional introgression of mitochondrial DNA in a hybrid population of tree frogs: The influence of mating behavior.

A total of 305 individuals from a hybrid population of North American tree frogs was characterized for allozyme and mitochondrial DNA (mtDNA) genotype. Species-specific mating behaviors had suggested the potential for directional hybridization, in which matings between Hyla cinerea males and Hyla gratiosa females numerically predominate over the reciprocal combination. Such directional bias leads to predictions about expected distributions of the female-transmitted mtDNA markers in F(1), backcross, and later-generation hybrids. These predictions were fully confirmed by the observed distributions of mtDNA genotypes among these allozymically inferred hybrid classes. Results exemplify the significance of stereotyped mating behaviors in determining the genetic architecture of a hybrid population.

Journal Article↗
PubMedDate not supplied

Size polymorphism and heteroplasmy in the mitochondrial DNA of lower vertebrates.

The mitochondrial DNA of the bowfin fish and each of two species of treefrogs displays large-scale size variation. Within each species, mitochondrial genomes span more than a 700 base pair range, and the size polymorphism is localized to one portion of the genome. In addition, about 5 percent of the total 357 individuals surveyed were observed to carry two size classes of mtDNA. These findings are among the few documented instances of extensive within-species mtDNA size polymorphism and individual heteroplasmy, and constitute exceptions to previously reached generalizations about the molecular basis of mtDNA variation.

Animals↗