UBC Theses and Dissertations
Spread of P elements in drosophila melanogaster Meister, Gerald Alan
Several experiments suggest that P elements spread in mixed P-M populations. These experiments monitored the spread of the ability of flies to induce and to suppress gonadal dysgenesis. Such experiments, based on physiological phenotypes and providing no molecular data, are unable to distinguish between the "dispersal" and "copy number accumulation" aspects of P element spread. This thesis describes several experiments undertaken to gain a fuller understanding of the various components of P element spread. The invasion of P elements in natural populations of Drosophila melanogaster was modelled by establishing laboratory populations with 0.5% and 5% P genomes. Two replicate populations at each frequency were monitored over twenty generations. The percentage of genomes that contained P elements was followed by single fly ovary blots at each generation for all populations. The distribution of P elements among individual flies was monitored by single fly Southern blots at even numbered generations from 6 to 20 for the two populations initiated with 5% P genomes. This analysis of the molecular dispersal of P elements is compared to the spread of the physiological phenotypes demonstrated by a collaborating lab. Our results show that the frequency of flies containing P elements increased each generation. The number of P elements within individual genomes decreased initially, but then increased to equal or surpass the number of elements in the parental P strain. Finally, the distribution of P elements within the genomes of individuals from later generations varied considerably, and this pattern differed from the original P strain. These results suggest that the interaction between the assortment and recombination of chromosomal segments, and some form of multiplicative transposition could result in the rapid spread of P elements in natural populations.
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