Article Abstract:
Analysis of the phenotypic effect of B chromosomes has been carried out over two years in a natural population of Japanese harvestman Metagagrella enuipes (Arachnida: Opiliones). Seasonal dynamics of the B chromosomes and effects of the odd-even condition and number of Bs on the phenotype and on M. tenuipes resistance to parasites were examined. In the B-even harvestmen infection was associated with reduced body size but no such association was seen in B-odd harvestmen. In the B-evens a U-shaped curve existed for number of Bs and the probability of being infected. An invested U was seen for body size and number of Bs. In the B-odd harvestmen there was no such association. Seasonal selection seems to be a major factor in the B-chromosome polymorphism.
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Article Abstract:
Effects of chromosome substitution on temperature-dependent selection in mtDNA transmission have been studied in artificially induced mitochondrial DNA (mtDNA) heteroplasmy in Drosophila. Chromosomes in two strains of D. melanogaster with different temperature dependency in mtDNA transmission were substituted reciprocally with mtDNA of D. mauritiana put in. Results indicate that the temperature-dependent selection in mtDNA transmission is co-operatively regulated by gene products encoded by the X, second and third chromosomes.
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Article Abstract:
Costs associated with nonsusceptibility were studied with the findings that nonsusceptibility of Biomphalaria glabrata to Echinostoma caproni was genetically determined and could be strongly selected for through generations. Analysis of age at maturity among offspring segregating for susceptibility showed that nonsusceptible individuals became mature later than susceptible ones. There is a cost to resistance.
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