genetic drift & genome architecture

Lynch M 2007 The origins of genome architecture. Sinauer. ISBN:9780878934843

• if the population size is sufficiently small, the noise associated with random gamete sampling can completely overwhelm weak selective forces
• this idea has long been appreciated in the field of molecular evolution (Kimura 1983; Ohta 1997)
• although small population size promotes the accumulation of mutations that are mildly deleterious in the short term, the resultant alterations to gene and genomic architecture can provide a potential setting for secondary adaptive changes that are unattainable in large populations
• central to this argument is a general reduction in the efficiency of selection across the transitions from prokaryotes to unicellular/origocellular eukaryotes to multicellular species, which results from the confluence of three factors:
• a decrease in population size
• a decrease in the amount of recombination between functionally relevant genomic sites
• an increase in the deleterious mutation rate
• (p. 70)