Law Of Segregation And Dominance

What is a Genetic Inheritance?

Inheritance is the acquiring of genetic characteristics or traits from parents by their offspring.

In the year 1860, Gregor Mendel unlocked the mystery of genetics. He cultivated pea plants and observed their pattern of inheritance from one generation to the next generation. His investigation led to the discovery of three laws of inheritance, famously known as Mendel’s Laws of Inheritance.

What are the Mendel’s Laws of Inheritance ?

The Law of Dominance, Law of Segregation and Law of Independent Assortment are the three Mendel’s laws of inheritance. These laws came into existence by the experiments on pea plants in a variety of differing traits. Mendel started his research with monohybrid cross.

What is monohybrid cross?

A monohybrid cross is a cross between the 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 then 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 the F1 generation had reappeared in the F2 generation. These observations led to the formulation of the Law of Dominance and the Law of Segregation.

monohybrid cross

In this section, let us know in brief about the two laws of inheritance, namely, Law of dominance and Law of segregation.

Law of Dominance

Law of dominance is known as the first law of inheritance. In this law, 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 the F1 generation and both parental characters will be expressed in the F2 generation in the ratio 3:1. The one which expressed in the F1 generation is called the 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 the dominant trait.

Law of Segregation

Law of segregation is the second law of inheritance. This law states that the pair of alleles segregates from each other during meiosiscell division (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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Practise This Question

A cross is made between breeding lines of pea plants with axillary and terminal flowers. If 1240 F2 progeny are obtained, how many of them produce terminal flowers?