NCERT Class 12 Biology Principles of Inheritance and Variation Notes (Handwritten Notes & PDF Download)

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NCERT Class 12 Biology Principles of Inheritance and Variation Handwritten Notes

Next Chapter: Molecular Basis of Inheritance
Previous Chapter: Reproductive Health

Other Subjects:
Class 12 Physics Notes
Class 12 Chemistry Notes

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Key Points: Principles of Inheritance and Variation Notes PDF

Genetics – It is a branch of biology which deals with Study of heredity and Variation.

Gregor John Mendel is known as Father of genetics.

Heredity – The study of transfer of character from one generation to another (next) generation is known as variations.

Inheritance – The process of transfer of character from one generation to next generation is known as inheritance.

Gregor John Mendel

Born on 22 july 1822 (Austria).
Mendel conducted experiments on Garden pea – (Pisum sativum) for 7 years 1856-1863. Mendel Published it in 1865 – by title named as “Experiment of plant Hybridisation”.
Death 1884 ,Mendel principles Mediscoved in 1900.

Reason of Mendel’s Success:

1. Mendel choose a right plant (Pisum sativum) far his experiment. Reason for Selection of pea plant
   • Short life span and easy to cultivate.
   • Large number of contrasting traits and large number of off springs produced.
   • Bisexual flower with self pollination.
   • Artificial hybridisation and cross – pollination can be performed.
2. He studied only two or one character at a time.
3. He kept statistical record. He was first to use statics and mathematics logic in biology.
4. Experiment had large sampling size. He confirmed his inferences on successive generation.

Law of Independent Assortment : When two pairs of traits are combined in a hybrid segregation of one pair of character is independent of other pair of character.

Allele of one gene is independently assarted (mixed) with allele of other gene during gamete formation. Due to it new phenotype form (round green, and wrinkled yellow) beside parental phenotype (round yellow and wrinkled green)

Chromosomal Machanism:

In this method sex of an offspring is determined by chromosome.

• Autosomes: These chromosomes are involved in any other function except for sex determination.
• Allosomes : These are involve in sex determination. These are different in male and female. This is also known as sex – chromosome or Heterosome.

Genetic disorders: Disorder due to changes or mutations in genetic material
. These disorders are birth and passed from parents to the next generation.

Thalassemia

• It is an autosomal – linked recessive blood disease.
• This defect arises due to mutation or deletion in the gene responsible for α and β chain formation in Haemoglobin.
• Due to it no synthesis of the Globin chain or a reduced rate of synthesis of the globin chain (α and β chain).

Phenylketonuria:

• Autosomal recessive trait.
• In born error in metabolism.

The affected individual lacks phenylalanine hydroxylase enzyme. This enzyme converts phenylalanine into tyrosine.

In this disease due to lack of enzyme phenylalanine accumulated and convents into phenylpyruvic acid and other derivatives.

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