Traditional Culture Encyclopedia - Traditional festivals - What are the concepts of selfing, orthogonality, backcrossing and test crossing in biology?
What are the concepts of selfing, orthogonality, backcrossing and test crossing in biology?
Self-pollination: the same plant has cross-pollination (including self-pollination and cross-pollination of the same plant).
Test crossing: F 1 or other organisms mating with invisible individuals can be used to determine the genotype or inheritance mode of the tested individuals.
1, two different genotypes, orthogonal and backcross, hybridize with B. If A is the male parent and B is the female parent, then B is the male parent and A is the female parent. Conversely, if B is the male parent and A is the female parent, then A is the male parent and B is the female parent. In practice, reciprocal crossing is often used to judge whether the inheritance mode of a character is nuclear inheritance or cytoplasmic inheritance. In nuclear inheritance, reciprocal crossing can also be used to judge whether it is autosomal inheritance or sex inheritance. When two parents cross with relative traits, if the offspring of orthogonal and backcross have the same traits, the traits belong to nuclear inheritance and are controlled by alleles on autosomes. For example, when high-stem peas cross with short-stem peas, both orthogonal and backcross F 1 are high-stem; If the results of orthogonal and backcross are different, the ratio of male and female offspring traits is not all 1: 1. If it shows the characteristics of cross inheritance, it belongs to nuclear inheritance and is controlled by alleles on the X chromosome. If flies backcross with Drosophila melanogaster.
2. The definition of test crossing was put forward by Mendel when he was verifying whether his explanation of trait segregation was correct. In order to determine whether F 1 is heterozygote or homozygote, F 1 is crossed with recessive homozygote, which is called test crossing. But sometimes even if an individual is known to be heterozygote, the mating between heterozygote and recessive homozygote is also called test crossing. At the same time, in the textbook, Mendel asked F 1 to test cross with double recessive individuals when verifying the explanation of two pairs of character recombination phenomena. When studying two pairs of relative traits, many students mistakenly think that it is called test crossing only when the parent combination is double heterozygosity and double recessive. In fact, any genetic law first originates from the observation of a pair of relative characters. When observing the genetic laws of two pairs of traits, we always observe them separately first, so as long as each pair of traits is a test cross, the whole combination is a test cross.
3. Self-pollination is the main mating mode of plants that are closed-pollinated, self-pollinated or pollinated by the same plant, such as peas and corn. The mating between dioecious plants with the same genotype is also called self-mating, but the mating between animals with the same genotype is generally not called self-mating, usually called free mating. In practice, self-crossing is mainly used to identify whether the inheritance of a pair of relative traits follows the phenomenon of gene separation, and can also be used to identify the genotype of a dominant plant. If individuals self-cross, if there are enough offspring, then the offspring will be heterozygous, and if there is no trait segregation, then the offspring will be homozygous. At the same time, in cross breeding, continuous selfing is the main method to obtain stable genetic purebred.
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