In order to compare the population dynamics of P elements in the sibling species D. melanogaster and D. simulans, three sets of studies were performed. In a series of comparative mixed population experiments, P-M mixed populations of D. melanogaster evolved into P or Q populations, depending on the strength of the P strains used as the original parental strains. However, no mixed populations of D. simulans evolved into P populations; even when the strongest P strains of D. simulans were used, all mixed populations evolved into Q or M' populations. Using an excision assay system, excision frequencies in a variety of strains of D. melanogaster and D. simulans were measured. On average, excision frequencies of P elements from plasmids were significantly lower in D. simulans than in D. melanogaster. In addition, there were no statistically significant correlations between GD sterility and excision frequencies. Using single neomycin -marked P elements, transposition frequencies of P elements were compared in D. melanogaster and D. simulans. As with excision frequencies, transposition frequencies were lower in D. simulans than in D. melanogaster. In addition, the position of the original insertion site had a strong effect on transposition frequency. All of these three experiments showed significantly lower average activity of P elements in D. simulans than in D. melanogaster. This consistency suggests that the three sets of results were influenced either directly and/or indirectly by common factors, such as host-encoded factors. Therefore, differences in the activity of P elements in these two species may be influenced by different host-encoded factors. The absence of P elements in natural populations of D. simulans may also be explained by the presence of different host factors.

The dynamics and changes in the pattern of the interstate migration system in India during the post-Independence period are explored. Three major perspectives, namely (i) the demographic effectiveness of net migration in changing the regional and ethnic balance of population distribution, (ii) the principal components or regional subsystems of in- and out-migration based on similarities in the origin and destination areas of migrants, and (iii) the shift-share components of the change in net migration are adopted to provide insight into the changing structure of interstate population movements in India. The major findings are compared with those of other similar studies done in the context of developed countries. The post-Independence development policies have had a significant impact in diffusing the highly polarized pre-Independence pattern of interstate migration in India.

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