Artificial selection is selective breeding by humans for desired characteristics. Usually genetic polymorphism exists for different characteristics i.e. each characteristic has distinctly different phenotypes. Farmers, breeders and horticulturalists breed plants and animals by interbreeding individuals with desired characteristics and selecting from the offspring and interbreeding the offspring over many generations.The disadvantage of inbreeding is that organisms that are closely related are likely to have the same harmful recessive alleles and these are selected for as well. Over time genetic disorders accumulate (inbreeding depression). Alleles from gene banks which store biological samples (seeds, eggs, sperm) can be used to increase genetic diversity.