Revision Notes on Inheritance and Variation Me | Allen Crash Course - Latest

Revision Notes on Inheritance and Variation


Mendel’s Law of Inheritance

(1) Mendelism means experiments performed by Mendel on genetics.

(2) Mendel’s experiment involved 4 steps as selection, hybridization, selfing and calculations. His results led to the formation of laws of genetics later.

(3) Mendel performed monohybrid and dihybrid crosses and gave three principles of inheritance.

(4) Mendel’s three principles of inheritance are:
(i) Law of dominance
(ii) Law of segregation or law of purity of gametes
(iii) Law of independent assortment

(5) Law of Dominance: The dominant characters are expressed when factors are in heterozygous condition.

(6) The recessive characters are only expressed in homozygous conditions. The characters never blend in heterozygous condition. A recessive character that was not expressed in heterozygous condition may be expressed again when it becomes homozygous.

(7) Law/Principle of segregation states that when a pair of contrasting factor or gene is brought together in a hybrid, these factors do not blend or mix up but simply associate themselves and remain together and separate at the time of gamete formation.

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(8) Principle of independent assortment states that genes of different characters located in different pairs of chromosomes are independent of one another in this segregation during gamete formation.

(9) Test Cross: A cross between F1 hybrid (Aa) and its homozygous recessive parent (aa) is called Test Cross. This cross is called test cross because it helps to find out whether the given dominant phenotype is homozygous or heterozygous.

(10) Monohybrid cross: When we consider the inheritance of one character at a time in a cross, this is called monohybrid cross.

(11) Dihybrid Cross: A cross made to study the inheritance of two pairs of contrasting traits.

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