Selfish genes are regions of DNA that enhance their transmission to subsequent generations, regardless of their impact on the host organism's fitness. Satellite DNA represents a class of selfish genes characterized by highly repetitive, non-coding nucleotide sequences. The 359bp satellite, located on the X-chromosome of Drosophila melanogaster, exemplifies one such sequence. Though its importance was initially downplayed, recent studies have revealed that DNA satellites like the 359bp are not only among the fastest-evolving sequences in eukaryotic genomes but also play critical roles in maintaining or threatening genome integrity. Moreover, satellite-interacting proteins have been shown to coevolve with these sequences to mitigate their potential deleterious effects.

Building on existing knowledge, this research project aims to:

1. Explore the genetic variation within and between D. melanogaster strains across the species globally.
2. Investigate protein-coding genes, particularly helicases, that are under positive selection.

By sequencing the 359bp satellite across ten worldwide D. melanogaster strains and performing multi-sequence alignment, the research employs PhyML to construct a phylogenetic tree, analyzing polymorphism both within and between strains at the 359bp locus. Phylogenetic analysis reveals minimal strain-specific genetic differences in 359bp satellite sequences. Furthermore, by comparing the ratio of synonymous (dS) to non-synonymous (dN) amino acid changes in the helicase protein sequences of D. melanogaster and its closely related species D. simulans, the study identifies several helicase proteins exhibiting signatures of positive selection.