In plants Crossing two genetically different plants produces a
hybrid seed. This can happen naturally, and includes hybrids between species (for example,
peppermint is a
sterile F1 hybrid of
watermint and
spearmint). In
agronomy, the term
F1 hybrid is usually reserved for agricultural
cultivars derived from two-parent cultivars. These F1 hybrids are usually created by means of controlled
pollination, sometimes by
hand pollination. For
annual plants such as tomato and
maize, F1 hybrids must be produced each season. For mass production of F1 hybrids with uniform phenotype, the parent plants must have predictable genetic effects on the offspring.
Inbreeding and selection for uniformity for multiple generations ensures that the parent lines are almost homozygous. The divergence between the (two) parent lines promotes improved growth and yield characteristics in offspring through the phenomenon of
heterosis ("hybrid vigour" or "combining ability"). Two
populations of breeding stock with desired characteristics are subjected to inbreeding until the homozygosity of the population exceeds a certain level, usually 90% or more. Typically, this requires more than 10 generations. Thereafter, the two strains must be crossed, while avoiding
self-fertilization. Normally, this is done with plants by deactivating or removing male flowers from one population, taking advantage of time differences between male and female flowering, or hand pollinating. In 1960, 99% of all
corn, 95% of
sugar beet, 80% of
spinach, 80% of
sunflowers, 62% of
broccoli, and 60% of
onions planted in the United States were F1 hybrids. Beans and peas are not commercially hybridized because they are
automatic pollinators, and hand pollination is prohibitively expensive.
F2 hybrids F2 hybrids, the result of self or cross-pollination of F1s, lack the consistency of F1s, though they may retain some desirable traits and can be produced more cheaply because hand pollination or other interventions are not required. Some seed companies offer F2 seed at less cost, particularly in
bedding plants, where consistency is less critical.
In animals F1 crosses in animals can be between two inbred lines or between two closely related species or subspecies. In fish such as
cichlids, the term F1 cross is used for crosses between two different wild-caught individuals that are assumed to be from different genetic lines.
Mules are F1 hybrids between
horses (mares) and
donkeys (jacks); the opposite sex cross results in
hinnies. However, such offspring are almost always sterile. Today, certain domesticated–wild hybrid breeds, such as the
Bengal cat and the
Savannah cat, are classified by their filial generation number. An F1 hybrid Savannah cat is the result of reproduction between an African Serval cat and a domestic cat. As explained in the International Journal of Fauna and Biological Studies, there are four reasons for species hybridizations: • Small population size •
Habitat fragmentation and species introduction • Anthropogenic hybridization • Visual, chemical, and acoustic interferences Small population size can be caused by inadequate or obliterated natural habitats that lead to species escaping to other habitats and as a result, this may lead to lesser mate availability and can cause breeding between distinct species. Habitat fragmentation and species introduction can be man-made or caused by mother nature such as deforestation,
desertification, eutrophication, urbanization, water oil extraction causing changes in the ecosystem that leads to animal migration or evading new surroundings. Third, is anthropogenic hybridization, which is "artificial or human-led hybridization" is supported for researchers to study "reproductive compatibility between species". Lastly, visual, chemical, and acoustic interferences cues are what causes species to signal sexual cues by differentiating between the same and opposite-sex leading to hybridization. == Advantages ==