Law of inheritance, Mendalian Inheritance, Terminology related to Mendelism


Terminology related to Mendelism

Mendel noticed two different expressions of a trait – Example: Tall and dwarf. Traits are expressed in different ways due to the fact that a
gene can exist in alternate forms (versions) for the same trait is called alleles.If an individual has two identical alleles of a gene, it is called as homozygous(TT). An individual with two different alleles is called heterozygous(Tt). Mendels non-true breeding plants are heterozygous, called as hybrids. When the gene has two alleles the dominant allele is symbolized with capital letter and the
recessive with small letter. When both alleles are recessive the individual is called homozygous
recessive (tt) dwarf pea plants. An individual with two dominant alleles is called homozygous dominant (TT) tall pea plants. One dominant allele and one recessive allele (Tt) denotes non- true breeding tall pea plants heterozygous tall.

Mendelian inheritance – Mendel’s Laws of Heredity

Mendel proposed two rules based on his observations on monohybrid cross, today these rules are called laws of inheritance The first law is The Law of Dominance and the second law is The Law of Segregation.These scientific laws play an important role in the history of evolution.The Law of Dominance: The characters are controlled by discrete units called factors which occur in pairs. In a dissimilar pair of factors one member of the pair is dominant and the other is recessive. This law gives an explanation to the monohybrid cross(a) the expression of only one of the parental characters in F1 generation and(b) the expression of both in the F2 generation. It also explains the proportion of 3:1 obtained at the F2

The Law of Segregation (Law of Purity of gametes):

Alleles do not show any blending, both characters are seen as such in the F2 generation although one of the characters is not seen in the F1 generation. During the formation of gametes, the factors or alleles of a pair separate and segregate from each other such that each gamete receives only one of the two factors. A homozygous parent produces similar gametes and a heterozygous parent produces two kinds of gametes each having one allele with equal proportion. Gametes are never hybrid.

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