F1 hybrid
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F1 hybrids are the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types, the offspring of which produce a new, uniform variety with specific and/or desirable characteristics from either or both parents. In fish breeding, those parents frequently are two closely related fish species, while in plant and animal genetics those parents usually are two inbred lines. Mules are F1 hybrids between horse and donkey. Crossing specific parent plants produces a hybrid seed (plant) by means of controlled pollination. To produce consistent F1 hybrids, the original cross must be repeated each season. As in the original cross, in plants this is usually done through controlled hand-pollination, and explains why F1-seeds are so expensive.
In agronomy the term "F1 hybrids" is usually reserved for agricultural cultivars where the parental types are two inbred and thus almost homozygous lines. Because of the almost pure homozygosity of the parent lines, F1 hybrids have a very high level of heterozygosity. As a result of this, F1 hybrids display improved growth and yield characteristics.
Production of F1 hybrids
In plants
Two populations of breeding stock with desired characteristics are subject to inbreeding until the homozygosity of the population exceeds a certain level, usually 90% or more. Typically this requires more than ten generations. After this happens, both populations must be crossed while avoiding self-fertilization. Normally this happens in plants by deactivating or removing male flowers from one population, taking advantage of time differences between male and female flowering or hand-pollinating[link].In animals
Unlike most plants, commonly bred fish species as well as all mammals and birds are not hermaphrodite, and therefore it is much easier to prevent self-fertilization during an F1 cross. F1 crosses in fish can be between two inbred lines or between two closely related fish species, such as cichlid subspecies.[link]. The cross is usually performed by natural or artificial insemination.Advantages
- Homogeneity and predictability - because of the homozygosity of the parent pure lines, there is next to no genetic variation between individual plants or animals. This makes their phenotype extremely uniform and thus attractive for mechanical operations and makes it easier to fine-tune the management of the population. Once the characteristics of the cross are known, repeating this cross will yield exactly the same result.
- Higher performance - As most non-junk DNA alleles code for different versions of a protein or enzyme, having two different versions of this allele amounts to having two different versions of the enzyme. This will increase the likelihood of having an optimal version of the enzyme present and reduce the likelihood of a genetic defect. This effect is referred to in genetics as the genetic hysteresis effect.
Disadvantages
- The main advantage of F1 hybrids is also their drawback. When F1 cultivars are used for the breeding of a new generation, their offspring will revert to the natural level of heterozygocity and thus will have a depression in yield. Of course, this is a desired characteristic from the point of view of the seed producer.
- Both inbreeding and crossing both lines requires a lot of work, which translates in a much higher seed cost. In general, the higher yield offsets this disadvantage.
- F1 hybrids usually give higher yields than traditional varieties, but only when they are grown using chemical fertilisers, pesticides, fungicides and herbicides. In contrast, traditional varieties usually have a higher natural resistance to disease. Therefore, large inputs of artificial chemicals are not usually necessary in order for them to grow well.
- F1 hybrids are bred to mature all at once. This is of interest for modern farmers, because all are ripen at the same time and can be harvested by machine. Traditional varieties are often more useful to gardeners because they crop over a longer period of time, avoiding gluts and famines.
- F1 hybrids are really clones of a parent plants (all the contrary of a "variety"). That means all offsprings share the same genetic code. This greatly reduces genetic diversity and, as a consequence, poor resistance to future plagues or climatic changes.
References
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