Inheritance is the acquiring of genetic characteristics or traits from parents by their offspring. In 1860, Gregor Mendel unlocked the mystery of genetics. He cultivated pea plants and observed their pattern of inheritance from one generation to next generation. His investigation led to the discovery of three laws of inheritance, famously known as Mendel’s Laws of Inheritance. In this section, two laws of inheritance, namely, Law of dominance and Law of segregation are discussed.
Law of Inheritance
Law of Dominance, Law of Segregation and Law of Independent Assortment are the three laws of inheritance. These laws come into existence by experiments on pea plants in a variety of contrasting traits. Mendel started his investigation with monohybrid cross.
A monohybrid cross is a cross between two monohybrid traits (TT and tt). Here plants which have the same characters but differ in only one character were crossed. For monohybrid cross, Mendel began with a pair of pea plants with two contrasting traits i.e., one tall and another dwarf. The cross-pollination of tall and dwarf plants resulted in tall plants and offspring were called F1 progeny.He continued his experiment with self-pollination of F1 progeny plants. This resulted in both tall and short plants in the ratio of 3:1. Mendel observed that traits which were absent in F1 generation had reappeared in F2 generation. These observations led to the formulation of Law of Dominance and Law of Segregation.
Law of Dominance
Law of dominance is known as the first law of inheritance. Each character is controlled by distinct units called factors, which occur in pairs. If the pairs are heterozygous, one will always dominate the other.
Law of dominance explains that in a monohybrid cross between a pair of contrasting traits, only one parental character will be expressed in F1 generation and both are expressed in F2 generation in the ratio 3:1. The one which expressed in F1 generation is called dominant trait and the one which is suppressed is called recessive trait. In simple words, the law of dominance states that recessive traits are always dominated or masked by dominant trait.
Law of Segregation
Law of segregation is the second law of inheritance. Law of segregation states that the pair of alleles segregates from each other during meiosis (gamete formation) so that only one allele will be present in each gamete. In a monohybrid cross, both the alleles are expressed in the F2 generation without any blending. Thus, the law of segregation is based on the fact that each gamete contains only one allele.
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