Self fertilization or autogamy is a reproductive strategy used by some species of plants. Autogamous plants tend to have fewer flowers and the flowers themselves tend to be smaller with smaller reproductive structures than those of plants that reproduce sexually. The flowers also have fewer ovules and less pollen. Self fertilization has advantages and disadvantages. If a species reproduces exclusively through autogamy, genotypes are replicated with little change. Sometimes, it is advantageous for a plant to produce offspring as similar to itself a possible in order to remain adapted to the niche it is established in. In addition, in extreme or marginal habitats, autogamy is a means through which reproduction can always occur even when crossing between plants is infeasible. One major disadvantage of self pollination is that, because many genes are homozygous with two of the same alles, there is a higher frequency of deleterious traits that only are expressed when the plant gets two recessive copies of an alle. Some strands of a plant that self pollinates may become sterile and surviving lines often have reduced vigor and fertility.