2. The law of gene free combination.

Mendel's law was published by the Austrian geneticist Grigo Mendel in 1865, which gave birth to the famous genetic law. He revealed two basic laws of genetics-separation phenomenon and free combination law, which are collectively called Mendel's genetic law.

1. Overview

Before Gregor Johann Mendel, there was no clear scientific explanation for the genetic phenomenon of children like parents. At that time, the popular fusion theory or mixed theory explained this phenomenon as: "some kind of liquid" mixed in the mother's egg and the father's sperm was the reason why the child inherited the characteristics of both parents. In contrast, Mendel's self-supporting particle theory predicts that it is a unitary granular substance, which determines the nature of parents. Due to the limitation of the technical level at that time, Mendel could not fully explain what the particles were here. We know that particles here are genetic factors. It can be said that Mendel laid a framework for the future theory of genetic factors, and this discovery is of historic significance.

Unfortunately, before Mendel's death, this discovery did not get enough attention. But it is not completely buried, such as1mid-9th century, William? Hawke, Albert? Brownbury, Ivan? Hyde Juma Hausen? Bailey and others mentioned Mendel's law in their respective papers. In addition, the Encyclopedia Britannica 188 1 has introduced Mendel's research.

1900, Hugo de Vries of the Netherlands, Karl Collens of Germany and erich von Chemak of Austria discovered this law again. After investigating the previous literature, I finally found Mendel's paper. And named this law "Mendel's Law". Collins named this law, and Mendel himself did not call it "the law".

2. Theory and application value

Theoretically, the law of free combination provides an important theoretical basis for explaining the biodiversity in nature. There are many reasons for biological variation, but the free combination of genes is an important reason for the diversity of biological characters. For example, a pair of biological hybrids with 20 pairs of alleles (these 20 pairs of alleles are located on 20 pairs of homologous chromosomes respectively) has 2 20 =1048576 possible phenotypes in F2. This can explain why there are so many kinds of creatures in the world.

Separation phenomenon also helps to better understand why close relatives can't get married. Because some genetic diseases are controlled by recessive genetic factors, these genetic diseases rarely appear under normal circumstances, but in the case of consanguineous marriage (such as cousin marriage), they may inherit the same disease-causing genes from their ancestors, thus greatly increasing the chances of offspring getting sick. Therefore, it is necessary to prohibit consanguineous marriage, which has been clearly stipulated in China's marriage law.

An important application of Mendel's genetic law in practice is plant cross breeding. In the practice of cross breeding, we can purposefully combine the excellent characters of two or more varieties, and then continue to purify and select through selfing, so as to get new varieties that meet the ideal requirements. For example, there are two varieties of tomatoes: one is resistant to yellow meat and the other is susceptible to red meat. It is necessary to cultivate a new variety with genetic stability, disease resistance and red meat. You can cross these two varieties of tomatoes, and a new variety with both disease resistance and red meat will appear in F2. Breeding it as a seed, after selection and cultivation, you can get the new tomato variety with genetic stability you need.

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What is the content of Mendel's genetic law?

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What is Mendel's law of heredity?

Isolation of 1. gene. 2. The law of gene free combination. Mendel's law was published by the Austrian geneticist Grigo Mendel in 1865, which gave birth to the famous genetic law. He revealed two basic laws of genetics-separation phenomenon and free combination law, which are collectively called Mendel's genetic law. 1. Overview Before Gregor Johann Mendel, there was no clear scientific explanation for the genetic phenomenon of children like their parents. At that time, the popular fusion theory or mixed theory explained this phenomenon as: "some kind of liquid" in the mother's egg and the father's sperm was the reason why the child inherited the characteristics of both parents. In contrast, Mendel's self-supporting particle theory predicts that it is a unitary granular substance, which determines the nature of parents. Due to the limitation of the technical level at that time, Mendel could not fully explain what the particles were here. We know that particles here are genetic factors. It can be said that Mendel laid a framework for the future theory of genetic factors, and this discovery is of historic significance. Unfortunately, before Mendel's death, this discovery did not get enough attention. But it is not completely buried, such as1mid-9th century, William? Hawke, Albert? Brownbury, Ivan? Hyde Juma Hausen? Bailey and others mentioned Mendel's law in their respective papers. In addition, the Encyclopedia Britannica 188 1 has introduced Mendel's research. 1900, Hugo de Vries of the Netherlands, Karl Collens of Germany and erich von Chemak of Austria discovered this law again. After investigating the previous literature, I finally found Mendel's paper. And named this law "Mendel's Law". Collins named this law, and Mendel himself did not call it "the law". 2. Theoretically speaking, the law of free combination provides an important theoretical basis for explaining the biodiversity in nature. There are many reasons for biological variation, but the free combination of genes is an important reason for the diversity of biological characters. For example, a pair of biological hybrids with 20 pairs of alleles (these 20 pairs of alleles are located on 20 pairs of homologous chromosomes respectively) has 2 20 =1048576 possible phenotypes in F2. This can explain why there are so many kinds of creatures in the world. Separation phenomenon also helps to better understand why close relatives can't get married. Because some genetic diseases are controlled by recessive genetic factors, these genetic diseases rarely appear under normal circumstances, but in the case of consanguineous marriage (such as cousin marriage), they may inherit the same disease-causing genes from their ancestors, thus greatly increasing the chances of offspring getting sick. Therefore, it is necessary to prohibit consanguineous marriage, which has been clearly stipulated in China's marriage law. An important application of Mendel's genetic law in practice is plant cross breeding. In the practice of cross breeding, we can purposefully combine the excellent characters of two or more varieties, and then continue to purify and select through selfing, so as to get new varieties that meet the ideal requirements. For example, there are two varieties of tomatoes: one is resistant to yellow meat and the other is susceptible to red meat. It is necessary to cultivate a new variety with genetic stability, disease resistance and red meat. You can cross these two varieties of tomatoes, and a new variety with both disease resistance and red meat will appear in F2. Breeding it as a seed, after selection and cultivation, you can get the new tomato variety with genetic stability you need.

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What is Mendel's law of heredity?

The phenomenon of gene separation is one of the three laws of genetics (the other two are the law of gene free combination and the law of gene linkage exchange). It was discovered by Austrian geneticist Mendel (1822 ~ 1844) through pea hybridization experiment. The contents are as follows: the first generation offspring produced by the parents P 1 (including gene pair aa) and P2 (including gene pair AA) with relative traits only show P1; The second generation offspring have both P 1 and P2 traits, and the ratio of P 1 to P2 traits is 3: 1. The law of free combination of genes, or the law of independent distribution of genes, is one of the three laws of genetics (the other two are the law of gene separation and gene chain exchange). It was discovered by Austrian geneticist G.J. Mendel (1822- 1844) through pea hybridization test. The contents are as follows: the alleles of genes on non-homologous chromosomes that determine different pairs of traits are separated when forming gametes, and different pairs of genes (non-alleles) do not interfere with each other and combine independently. Mendel found that the gene segregation ratio was 9:3:3: 1 when he did two pairs of hybridization experiments of relative traits. The essence of gene linkage exchange law is that when meiosis forms gametes, different genes located on the same chromosome are often linked together to enter gametes; When meiosis forms tetrads, alleles on homologous chromosomes are sometimes exchanged with the exchange of non-sister chromatids, leading to gene recombination. It should be noted that the law of gene linkage exchange is not contradictory to the law of gene free combination, but a genetic law that occurs in different situations: two pairs (or more pairs) of genes located on non-homologous chromosomes are passed on to future generations according to the law of free combination, while two pairs (or more pairs) of genes located on homologous chromosomes are passed on to future generations according to the law of linkage exchange.

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The content of Mendel's genetic law

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Details of Mendel's law of heredity

In the process of meiosis, the paired genetic factors that determine a trait in the hybrid are separated from each other and do not interfere with each other, so that only one of the paired genetic factors exists in the gamete, thus producing two types of gametes with the same number and passing them on to the offspring independently. This is separation of mendelian law. When parents with two (or more) pairs of relative traits cross, when F 1 produces gametes, at the same time of allele separation, non-alleles on non-homologous chromosomes show free combination, which is the essence of the law of free combination. That is to say, the separation and combination of one pair of alleles and another pair of alleles do not interfere with each other, and they are assigned to gametes independently.

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What are the contents of the three laws of heredity?

Separation of mendelian law Mendel's Free Binding Chain and Exchange Law separation of mendelian law is one of Mendel's genetic laws. Mendel judged that there were a pair of alleles of relative traits in the individuals of the first generation hybrid (F 1), but they still kept their individuality, separated from each other during gamete formation and entered a gamete cell respectively. Separation is the most fundamental phenomenon in Mendel's law. Generally speaking, in a homozygote, two genes from parents occupying the same gene position on the same chromosome will never fuse but still maintain their individuality. However, in the process of gamete formation, the genes will separate, resulting in the separation of the second generation (F2) and the recurrent (B 1) traits. In heterozygote cells, they are located on a pair of homologous chromosomes and have certain independence. When an organism undergoes meiosis to form a gamete, the alleles will separate with the separation, enter two gametes respectively, and be passed on to the offspring independently with the gametes. Mendel's law of free combination is the best in a large number of plant hybridization experiments that Mendel has engaged in. After eight years' unremitting efforts (1856- 1864), the paper "Plant Hybridization Experiment" was finally published in 1865, which put forward the argument that genetic unit is genetic factor (called gene in modern genetics) and revealed two basic laws of genetics-separation phenomenon and the law of free combination. The discovery and presentation of these two important laws laid a solid foundation for the birth and development of genetics, which is also an important scientific research achievement that Mendel will leave behind. The Law of Chain Interchange 19 10, Morgan of Columbia University (1866- 1945) and several of his students started the genetic research on Drosophila. Drosophila Morgan is a small insect, which is common in fruit stalls in summer. It has a pair of small red eyes. When Morgan experimented with fruit flies for the first year, they found a male white-eyed fruit fly, which was spontaneously mutated by red-eyed fruit flies. When male Drosophila melanogaster mates with female Drosophila melanogaster, the offspring are all red-eyed Drosophila melanogaster, indicating that the red color of eyes is dominant to the white color. When F 1 red-eyed male Drosophila melanogaster mates with female Drosophila melanogaster, the ratio of red eye to white eye in F2 generation is still 3: 1, but there is no male-female relationship, and all white-eyed Drosophila melanogaster are male, which shows that because white eyes are related to gender, it is called sex linkage. Color blindness and hemophilia in humans are also X-linked.

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