Law of Mendel
Gregor John Mendel did genetic research on the pea plant growing in the garden, which we studied under the title Gregor John Mendel and Mendel's Hybridization Experiment. In this hybridization experiment, Mendel removed the stamens from female pea plants and took pollen from the stamen of another plant and put it on the stigma of the flower of the first plant. In this way, an attempt was made to obtain plants with desired characteristics by artificial pollination. After the completion of this experiment, Mendel published the facts related to his research in the form of Mendel's law of inheritance. There are mainly three rules under this, which are as follows –
- Law of Dominance
- Law of Segregation or Law of Purity of Gametes
- Law of Independent Assortment
1. Law of Dominance
In the use of a monohybrid hybridization, when plants with two opposing characteristics of the same character are crossed, the first generation (F 1) exhibits the same character, which is dominant. This is called the Law of Dominance. The quality or factor which appears in this action, or which does not allow the other quality to appear, is called the Dominant factor. While that quality which does not appear, it is called recessive factor.
Example – To confirm Mendel's rule, when hybridization is done between homozygous tall (TT) plant and homozygous dwarf (tt) plant of pea, then as a result of hybridization in the first generation (F 1) The plants obtained were all heterozygous tall (Tt). Which confirms the Law of Dominance. And the trait of tallness was displayed in the F1 generation, which was called the dominant trait. Whereas the trait which was not displayed, that is, the trait of dwarfism was called recessive traits.
It is clear from this that each gene has many pairs of alleles and one of them is dominant and the other is recessive. The dominant trait appears in both homozygous ( T T ) and bizygous ( T t ) conditions. While the recessive trait appears only in the homozygous ( t t ) state.
2. Law of Segregation Or Law of Purity of Gametes
According to Mendel's law, the factors of each gene pair are separated from each other at the time of formation of gametes and go to different gametes and in the formation of zygote, these factors again: They come with others and maintain their existence. In this way, due to the gene or factor maintaining its existence or the purity of the gene, this rule is called the law of purity of gametes.
Example – In Mendel's law of dominance, when self-pollination is allowed to occur in hybrid tall plants obtained from the first generation (F1), the separation of gametes in the second generation (F2) takes place (Law of Segregation). are | In this way plants with different characters are obtained in the F2 generation.
If we see according to the phenotype, three plants are tall, while one plant is dwarf, that is, 75% plants are tall and 25% plants are dwarf. Whose ratio is 3 : 1.
If we see according to genotype, one plant is pure tall, two plants are hybrid tall and one plant is pure dwarf, that is, 25% plants are pure tall, 50% plants are hybrid tall and 25% plants are pure dwarf. Whose ratio is 1 : 2 : 1.
Reasons for Mendel's Success - Genetics3. Law of Independent Assortment
According to Mendel's law, it is based only on dihybrid and multihybrid hybridization. In this, when a pea plant having yellow and round shaped seeds (RRYY) is crossed with a pea plant having green and wrinkled shaped seeds (rryy), then in the first generation (F1) all plants have yellow and round shaped seeds (RrYy). ) are obtained. Due to which it is proved that yellow and round shape are effective symptoms. But when self-fertilization takes place in the second generation (F2), there is a separation of genes and re-conjugation of genes, mainly four types of plants are obtained.
- yellow and spherical seeded plants
- green and wrinkled seed plants
- yellow and wrinkled seed plants
- Green and round-seeded plants
The ratio of 9 : 3 : 3 : 1 is obtained between the above plants.
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