Gregor John Mendel is considered as the father of the genetic. He worked on pea plant and selected seven pairs of contrasting characters in the pea plant. Gregor John Mendel performed the following two hybridization experiments in pea plants:
Monohybrid cross When the cross is made between a single pair of contrasting character trait, it is known as monohybrid cross. For monohybrid cross Mendel selected a tall (TT) and a dwarf (tt) of garden pea Pisum sativum . When Mendel crossed these pants, all the offsprings were tall. The initial cross between two varieties is known as parental or P1 generation and their offsprings are called first filial generation or F1 generation. This process of obtaining new plants (hybrid) is called hybridization. When these plants are allowed to self-pollination , the tall and dwarf plants are produced in the ratio of 3:1 (75% tall and 25% dwarf). The offsprings of F1 generation form F2 or second filial generation. The succeeding generation of this cross is called F3 generation.
All the offsprings of F1 generation would be tall. Although it contains both the gene of tallness (T) and dwarfness (t) but only the characters of tallness would be expressed in F1 generation. The character which was expressed in F1 generation was called as the dominant character by Mendel. Likewise, the character of dwarfness which would not be expressed in F1 generation was called as the recessive character.
These tall plants of F1 generation was allowed to self-fertilization (self-pollination). The tall and dwarf plants produced in the ratio of 3:1. It means F2 generation consisted of three types of plants:
On the basis of experiment, Mendel found that although the genes for tallness and dwarfness remain together in F1 generation they would be segregated in F2 and subsequent generations without mixing. Thus, he concluded that the genes of one trait do not affect the genes of another trait. Mendel also found that the gametes of F1 offsprings will always be pure. Mendel called it as the purity of gametes.
Dihybrid cross When a cross is made between two pairs of contrasting character traits, it is known as dihybrid cross. For dihybrid cross, Mendel selected garden pea having two pairs of contrasting characters:
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When these plants are cross-pollinated in F1 generation, they produced hybrid plant (RrYy) with round and yellow seeds, because of the presence of dominant genes "R" and "Y". When these plants (F1) were allowed to self-pollination, following four types of progenies were formed in F2 generation in the ratio of 9:3:3:1.
Laws of inheritance or Mendelism On the basis of monohybrid cross Mendel formulated two laws ( law of dominance and law of segregation) and on the basis of the dihybrid cross, Mendel formulated the law of independent assortment. The three laws are as follows:
Biological significance of Mendel's Law The significance of Mendelism are as follows:
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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