Class 12 Biology Chapter 4 Principles of Inheritance and Variation Notes (Short and Handwritten Notes PDF)

Hi students,

If you are a class 12 student and looking for a nice and simple notes for chapter 4 “Principles of Inheritance and Variation” of Biology, then you are at the right place. This chapter is very important for board exams, and our notes will make your preparation extremely easy.

These notes are specially created by analyzing NCERT latest syllabus and last 10 years board exam question papers.

In this article, we have given complete notes of Class 12 Biology Chapter 4 Principles of Inheritance and Variation Health (NCERT Class 12 Biology). In this note, every point is written in easy language so that you can understand this lesson easily. This note is based on NCERT. That is, this note is useful for all those children who study NCERT in English medium.

Here we have given the Notes in PDF format which you can download so that you can print it and save your time. To download, click on the given Download PDF link.

Principles of Inheritance and Variation Notes PDF Download

Important topics covered in the notes

• Mendel’s Laws of Inheritance
  • Reasons for Mendel’s success.
  • Inheritance of One Gene (Monohybrid Cross).
  • Law of Dominance.
  • Law of Segregation.
• Inheritance of One Gene
• Deviations from Mendelism:
  • Incomplete Dominance.
  • Co-dominance.
  • Multiple Alleles (e.g., ABO blood grouping in humans).
• Inheritance of Two Genes
  • Dihybrid Cross.
  • Law of Independent Assortment.
• Chromosomal Theory of Inheritance
  • Contributions of Sutton and Boveri.
  • Experimental verification by Thomas Hunt Morgan on Drosophila.
  • Linkage and Recombination.
• Sex Determination
  • Mechanisms of sex determination in different organisms (Humans, Birds, Insects).
  • Sex determination in Humans.
• Mutation
  • Gene mutations and Chromosomal aberrations.
• Genetic Disorders
• Pedigree Analysis
• Mendelian Disorders:
  • Haemophilia
  • Sickle-cell Anaemia
  • Phenylketonuria
  • Thalassemia
• Chromosomal Disorders:

Principles of Inheritance and Variation Notes – lesson summary

1. Genetics-It is the branch of biology which deals with inheritance and variations of characters from parents to offspring.
2. inheritance: It is the process of passing characters from parent to progeny. It is the basis of heredity.
3. Variation-It is the degree by which progeny differs from parents. Variations can be in terms of physiology, morphology and behavioral characteristics
4. Mendel’s Law Of Inheritance: Mendel conducted hybridization experiments on garden peas for seven years (1856-1863). On the basis of experiments.
5. Gene: It is the unit of inheritance. It contains information that is required to express a particular trait in an organism.
6. Law of Dominance: The dominant allele masks the effect of recessive allele. It explains the expression of only one of the parental characters
7. Law of Segregation: It states that every individual possess two alleles of a gene and these alleles segregate from each other during gamete formation (at the time of meiosis).
8. inheritance of two Gene: Mendel also worked with two characters on pea plants.
   • Phenotypic Ratio- Round yellow : round green : wrinkled yellow : wrinkled green
9. Mendelian Disorders: Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.
10. Linkage And Recombination: Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex linked.

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