Ocham’s razor
The principle that the least complicated explanation (most parsimonious hypothesis) generally should be accepted to explain the data at hand.

offsite conservation
See ex situ conservation.

outbreeding depression
The relative reduction in the fitness of hybrids compared to parental types.

outlier loci
Loci that may be under selection (or linked to loci under selection) that are detected because they fall outside the range of expected variation for a given summary statistic (e.g., extremely high or low FST compared to most “neutral” loci in a sample).

overdominance
See heterozygous advantage.

overlapping generations
A breeding system where sexual maturity does not occur at a specific age, or where individuals breed more than once, causing individuals from different brood years to interbreed in a given year.