Drive-selection equilibrium: homopolymer evolution in the Drosophila gene mastermind

Area of Science:

• Evolutionary genetics
• Molecular evolution
• Population genetics

Background:

• The Drosophila mastermind (mam) gene contains highly repetitive homopolymer domains.
• Length variation in these homopolymers is attributed to nucleotide misalignment during DNA replication or repair, leading to slippage mutations.

Purpose of the Study:

• To statistically test the hypothesis that conserved amino acid distances between charge clusters in the mam gene arose by chance.
• To investigate the interplay between molecular drive and natural selection in repetitive DNA sequences.

Main Methods:

• Interspecific sequence comparison of the Drosophila mastermind (mam) gene.
• Statistical analysis to test the null hypothesis of random amino acid distance similarity.
• Development of a model for drive-selection equilibrium in homopolymers.

Main Results:

• Extensive length variation was observed in homopolymer domains of the mam gene across Drosophila species.
• Statistical tests suggest that the observed similarity in amino acid distance between conserved charge clusters is unlikely to be due to chance.
• Evidence indicates a balance between length variability driven by molecular drive and length conservation imposed by natural selection.

Conclusions:

• The mam gene exemplifies the coexistence of length variability and conservation driven by molecular drive and natural selection, respectively.
• The findings extend theories of drive-selection interaction to homopolymer sequences.
• Homopolymer domains contribute significantly to genetic variation in natural populations due to their flexibility and variability.