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Genetic erosion (also known as genetic depletion) is a process in which the gene pool of a species diminishes, often accelerated by human activities. The term is sometimes used in a narrow sense, such as when describing the loss of particular alleles or genes, as well as being used more broadly, as when referring to the loss of a phenotype or whole species.

Low genetic diversity in a population, as a result of inbreeding and genetic drift, can increase the likelihood of a species going extinct. Small populations are more susceptible to genetic erosion than larger populations.

Many species benefit from a human-assisted breeding program to keep their population viable, thereby avoiding extinction over long time-frames.

Loss of agricultural biodiversity
Genetic erosion in agriculture and livestock is the loss of biological genetic diversity, including individual genes or recombinants of genes or gene complexes. Researchers were concerned with the loss of landraces as early as 1914. Genetic erosion has been quantified as absolute loss of a genetic unit, loss of richness, and reduction in evenness. Depending on the method of quantification, hybridization between landraces and modern cultivars can be considered genetic erosion of local resources. Genetic erosion is most prevalent in Europe and North America, where uniformity of modern cultivars is most common. De novo genetic diversity through modern breeding is generally considered to not slow the process of genetic erosion of crops. In the case of Animal Genetic Resources for Food and Agriculture, major causes of genetic erosion are reported to include indiscriminate cross-breeding, increased use of exotic breeds, neglect of certain breeds because of a lack of profitability or competitiveness, and the effects of diseases and disease management. In plants, vegetables were found to have a higher rate of genetic erosion than other crop categories, and in animals, a larger percent of mammal breeds have already gone extinct compared to avians.

Prevention and Safeguards
Modern policies of zoo associations and zoos around the world have begun putting dramatically increased emphasis on keeping and breeding wild-sourced species and subspecies of animals in their registered endangered species breeding programs. These specimens are intended to have a chance to be reintroduced and survive back in the wild. The main objectives of zoos today have changed, and greater resources are being invested in breeding species and subspecies for then ultimate purpose of assisting conservation efforts in the wild. Zoos do this by maintaining extremely detailed scientific breeding records (i.e. studbooks)) and by loaning their wild animals to other zoos around the country (and often globally) for breeding, to safeguard against inbreeding by attempting to maximize genetic diversity however possible.

Costly (and sometimes controversial) ex-situ conservation techniques aim to increase the genetic biodiversity on our planet, as well as the diversity in local gene pools. by guarding against genetic erosion. Modern concepts like seedbanks, sperm banks, and tissue banks have become much more commonplace and valuable. Sperm, eggs, and embryos can now be frozen and kept in banks, which are sometimes called "Modern Noah's Arks" or "Frozen Zoos". Cryopreservation techniques are used to freeze these living materials and keep them alive in perpetuity by storing them submerged in liquid nitrogen tanks at very low temperatures. Thus, preserved materials can then be used for artificial insemination, in vitro fertilization, embryo transfer, and cloning methodologies to protect diversity in the gene pool of critically endangered species.

Recently, strategies for finding an integrated approach to in situ and ex situ conservation techniques have been given considerable attention, and progress is being made.