Law of Dominance:

It states that in crossings between organisms (pure for contrasting characters of a pair) only one character of the pair appears in the F generation. In Mendelian termology a character that shows up itself in F1 is the dominant and the white is recessive.

Such pairs of contrasting char­acters are called allelomorphic pairs or allelic pairs and each member of a pair is said to be the allele of the other. It may be mentioned that the gametes do not carry characters as such but they carry some hereditary units, which are responsible for the appearance of characters in the off­spring. These hereditary units have been called factors or determiners.

They are now called genes. In gen­eral, the ability to synthesize an ac­tive enzyme qualifies a gene as a dominant. The presence of domi­nant gene in the diploid cell also usually permits the formation of a specific enzyme at a rate sufficient to allow growth.

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Law of Segregation:

The law of segregation of characters states that when a pair of allels are brought together they segregate without mixing and separate from each other when the hybrid forms gam­etes. According to this law, F, hy­brid tall pea of Mendel’s experi­ment will produce two kinds of gamesters some carrying the factor for tallness, and an equal number carrying the factor for dwarfness, the law is also known as the law of the purity of gametes.

It will be evident that the original tall plant will have two genes for tallness TT, having received one from each of its two parents. Similarly the dwarf plant will each have genes and the gametes of the dwarf parent will have a factor t each.

Their union will form an F, hybrid carrying the factors Tt. This hybrid will be tall because of dominance of ‘T’ and ‘t’ separate from each other and the result is the formation of two kinds of gametes in equal numbers, half carrying the factor T and half carrying the factor t. This is in accordance with Mendel’s law of segregation of characters.