Mendel’s Law of Inheritance or Mendelian genetics
Mendel’s
law of hereditary are described in his paper “Experiments on plant
hybridisation” which was published in the fourth volume of Annual proceeding of
Natural History Society of Brunn”
In
1900, Mendel’s paper was simultaneously discovered by three biologists: Hugo de
Vries, Carl Correns and Eric von Tschermark. The discovery of Mendelian
principles leads to the emergence of a new branch of biology known as Genetics.
William Bateson (1905) gave this developing science the name genetics’. Later
Johannsen coined the term gene for the hereditary unit that determines
observable characters.
Mendel’s
Law of Inheritance or Mendelian genetics
It is a set of primary tenets that underlie
much of genetics by G. Mendel In the latter part of 19 th century. He performed
monohybrid and dihybrid crosses and gave three principles of inheritance.
Mendel’s
three principles of Inheritance are:
2. Law of Segregation
3. Law of Independent Assortment
1. Law of Dominance
It
state that when two individuals of a species, differing in a pair of
contrasting characters are crossed, the form of the trait that appears in the
F1 hybrid is dominant and the other form that is not expressed is recessive.
In a
cross between tall and dwarf garden pea plants in the F1 generation only tall
plants are seen. This means that tall form is dominant over dwarf form.
Exceptions
to principle of dominance are incomplete dominance and codominance.
2. Law of Segregation
A
cross involving contrasting expression of one trait is referred to as mono
hybrid cross. For example, in order to learn inheritance of plant height, a
tall pea was crossed with dwarf one; all other traits were ignored here. From
the results of monohybrid crosses Mendel developed the law of segregation.
It
states that hereditary patterns are determined by factors that occur in pairs
in an individual but segregate from each other in the formation of gametes so
that any one gamete receives one or the other of the paired factors. This
principle is also known as the law of purity of gametes.
3. Law
of Independent Assortment
A
cross in which the parents differ in two pairs of alleles is called a Dihybrid cross
(example-tall green x dwarf yellow).
(example-tall green x dwarf yellow).
It
states that in the inheritance of two pairs of contrasting characters, the
factors of each pair of characters segregate independently of the factors of
the other pair of characters.
Importance
of Mendelism are
1. Science of eugenics (development of superior
progeny) is based on mendelism.
2. On the basis Mendelism, different breeds in animals and varieties of plants have been produced.
3. On the basis of Mendelism, heterosis has been utilised in different organism.
2. On the basis Mendelism, different breeds in animals and varieties of plants have been produced.
3. On the basis of Mendelism, heterosis has been utilised in different organism.
Tags:
Genetics Notes
Independent Assortment
Law of Dominance
Law of Segregation
Mendelian Genetics notes
Mendelism
Monohybrid and dihybrid cross