Through processes known as selective breeding and hybridization, farmers and other plant breeders create crops that have many desirable characteristics and few undesirable ones. For the most part, the desired outcomes of these procedures are either an increased yield or better quality crops. Some of the characteristics that are bred for are: bigger flower blooms, better taste, richer color and increased tolerance to heat, cold or drought.

Selective breeding uses plants that exhibit the most desirable traits to pollinate for seed. The future crops that are produced from this seed are in some way better than the original plant. Hybridization is the process by which a breeder combines desirable traits from two or more varieties to produce a plant that will be self-pollinated. This plant is superior to its parents in many respects.

Cross-pollination occurs when the egg cell in a flower of one plant is fertilized by the sperm cell from another plant of the same species. This leads to a more varied offspring than that which results from self-pollination because it has a mixture of the traits of both of its parents. It ensures that a beneficial gene that occurs in a single plant will be transferred to numerous offspring in a relatively short amount of time. Plants that are cross-pollinated also generally produce more and better seeds. They are also more likely to be able to adapt to changes in their environment whereas self-pollinated plants can not because they may contain traits that make them more successful in resisting climate changes or new predatory insects. Cross-pollination can occur naturally in numerous ways. Pollen from one flower can be transferred to another on the feet of insects such as bees, by the wind, or through birds or other animals. Many plants are equipped with mechanisms designed to encourage cross-pollination and discourage self-pollination.

Traits can be either dominant or recessive. A dominant allele will mask the effects of a recessive allele if the two are paired together on a gene. This means that if the dominant trait in a certain species of plant is large leaves and the recessive trait is small leaves, a plant having one dominant gene and one recessive gene will still have large leaves. In this example, the only way that the plant could have small leaves is if it inherited two recessive genes, one from each of its parents. Plant breeders want to cross plants in order to produce offspring with superior traits. This is accomplished by keeping a careful record of parent-offspring relationships and in each successive generation crossing only the plants that have the desired trait.

The above-mentioned techniques can be used to produce better crops. For example, in the 1960s during the "Green Revolution," new strains of wheat and rice were developed that produce increased yields when fertilized. The plants were selectively bred to be shorter, have smaller root systems and smaller leaves. These respond better to the fertilizer than the traditional varieties which grew too tall when fertilized and fell over in the wind and rain.

As a result of these techniques, a larger number of plants can be grown in the same area thus increasing the wheat and rice yield of the region. On a certain type of tomato species, the Lycopersicon hirsutum, the normal yearly improvement for the traits of yield, soluble solids content, and fruit color is approximately 1% per year. Other plants are selectively chosen for their ability to survive on less water and are planted in areas prone to drought. Still others are selected because they can withstand more extreme temperatures than traditional varieties. These crops can be planted in regions that have more extreme climates thus increasing the area of potential farmland in the world.

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