Genetic error, sex, and diploidy

Area of Science:

• Evolutionary Biology
• Molecular Biology
• Genetics

Background:

• Haploid cells are efficient replicators, while diploid cells exhibit resistance to DNA damage.
• The evolutionary origins of sexual reproduction and diploidy are explored in the context of DNA repair.
• Natural bacterial transformation is investigated as a model system for studying the evolution of sex.

Purpose of the Study:

• To test the hypothesis that sex and diploidy evolved as a DNA repair system.
• To model the selection dynamics between asexual haploids, sexual haploids, and diploids.
• To experimentally investigate the adaptive response of bacterial transformation to DNA damage.

Main Methods:

• Development of mathematical models simulating competition between different cell types (asexual haploid, sexual haploid, diploid).
• Analysis of parameter space bifurcation diagrams to determine conditions favoring each cell type.
• Experimental study using Bacillus subtilis to assess transformation frequencies in response to DNA damage.

Main Results:

• Mathematical models indicate that haploids thrive in low-damage environments, while diploids excel in high-damage, low-mortality conditions.
• Competitive coexistence between asexual diploids and sexual haploids is possible, with sex potentially increasing from rarity through mating with asexual cells.
• Experiments show that bacterial transformation frequencies adaptively respond to DNA damage when homologous donor DNA is present.

Conclusions:

• Sex and diploidy provide significant advantages in DNA repair, enabling organisms to cope with high mortality and DNA damage.
• Natural bacterial transformation may function as a DNA repair mechanism, with adaptive responses observed under DNA-damaging conditions.
• The study supports the hypothesis that DNA repair is a key factor in the evolution of sex and diploidy.