Genetic stochasticity refers to changes in the genetic composition of a population unrelated to systematic forces (selection, inbreeding, or migration), i.e., genetic drift. It can have a large impact on the genetic structure of populations, both by reducing the amount of diversity retained within populations and by increasing the chance that deleterious recessive alleles may be expressed. The loss of diversity could limit a population's ability to respond adaptively to future environmental changes. In addition, the increased frequency with which deleterious recessive alleles are expressed (because of increased homozygosity) could reduce the viability and reproductive capacity of individuals. I am generally skeptical about the extent to which genetic stochasticity poses a threat to most endangered species of animals or plants, for reasons we'll discuss in some detail later. For now, suffice it to say that most frequently I suspect the lack of genetic diversity in endangered species is a symptom of their endangerment, not a cause.