Evaluating forensic biology results given source level propositions

The evaluation of forensic evidence can occur at any level within the hierarchy of propositions depending on the question being asked and the amount and type of information that is taken into account within the evaluation. Commonly DNA evidence is reported given propositions that deal with the sub-source level in the hierarchy, which deals only with the possibility that a nominated individual is a source of DNA in a trace (or contributor to the DNA in the case of a mixed DNA trace). We explore the use of information obtained from examinations, presumptive and discriminating tests for body fluids, DNA concentrations and some case circumstances within a Bayesian network in order to provide assistance to the Courts that have to consider propositions at source level. We use a scenario in which the presence of blood is of interest as an exemplar and consider how DNA profiling results and the potential for laboratory error can be taken into account. We finish with examples of how the results of these reports could be presented in court using either numerical values or verbal descriptions of the results.

Genetic variation and evolutionary divergence within and among populations, species, and genera of the Cambarinae

Seven crayfish species from three genera of the subfamily Cambarinae were electrophoretically examined for genetic variation at a total of twenty-six loci. Polymorphism was detected primarily at three loci: Ao-2, Lap, and Pgi. The average heterozygosities over-all loci for each species were found to be very low when compared to most other invertebrate species that have been examined electrophoretically. With the exception of Cambarus bartoni, the interpopulation genetic identities are high within any given species. The average interspecific identities are somewhat lower and the average intergeneric identities are lower still. Populations, species and genera conform to the expected taxonomic progression. The two samples of ~ bartoni show high genetic similarity at only 50 percent of the loci compared. Locus by locus identity comparisons among species yield U-shaped distributions of genetic identities. Construction of a phylogenetic dendrogram using species mean genetic distances values shows that species grouping is in agreement with morphological taxonomy with the exception of the high similarity between Orconectespropinquus and Procambarus pictus. This high similarity suggests the possibility of a regulatory change between the two species. It appears that the low heterozygosities, high interpopulation genetic identities, and taxonomic mispositioning can all be explained on the basis of low mutation rates.

Seasonal variation in the reproductive biology of the ring -billed gull (Larus delawarensis)

The reproductive biology of the Ring-billed Gull (Larus delawarensis) was studied on Gull Island, Presqu'ile Provincial Park, Ontario, in 1976 and 1977. Early started clutches (comprising the majority of clutches on Gull Island) in 1977 produced more chicks per nest (2.20 ± 0.09) than late started clutches (0.86 ± 0.13) as a result of reductions in mean clutch size, hatching success and fledging success with date of clutch initiation. Seasonal changes in mean clutch size, hatching success and fledging success also resulted in early clutches, initiated at the peak of clutch starts, producing more chicks per nest (2.34 ± 0.11) than either pre-peak (2.13 ± 0.20) or post-peak (1.82 ± 0.29) clutches. Possible reasons for these trends, including the observed predominance of immature plumaged, breeding gulls in late started areas, are discussed. Clutches were deserted at night for varying lengths of time from at least 15 April until 10 May, 1977. It is suggested that this nocturnal desertion behaviour resulted in the enhancement of inter- and intra-clutch hatching synchrony in early started areas and further, that this may in part explain the existence of the behaviour in terms of its adaptive significance.