Principal of Inheritance and Variations ; Class 12th Notes + important digrams+ NEET Important question and Weightage Full Explanation is Here

 1. Introduction 

  • Genetics = study of heredity and variation
  • Heredity = Transfer of traits from parents to there offsprings 
  • Variation = Difference among individuals
This chapter explains how traits pass and why variations occur 

First we discuss about this chapter Weightage 
Expected questions : 4-5 questions every year
Marks : 16 - 20 marks we discuss about NEET important questions in last section so don't skip 

2. Important Terminology 

  • Gene - unit of inheritance 
  • Allele - Alternative form of gene
  • Homozygous - Same allele (TT, tt)
  • Heterozygous - Different allele (Tt)
  • Phenotype - Physical apperance 
  • Genotype - Genetic makeup

3. Mendel Experiment 

Diagram : Mendel pea Plant Traits 


You will get Digrams in this Telegram channel so don't forget to join

Scientist: Gregor mendel (Father of Genetics)
Plant used : Pisum sativum (pea plant)

Why Mendel choose pea plant ?
  • Short Life cycle
  • Easily crossed pollinated 
  • Clear Contracting traits 

4. Mendel's Law ( very important )

1. Law of Dominance 

  • Dominant Allele expresses
  • Recessive Hidden

2. Law of segregation (most important)

  • Alleles Seperate during gametes formation

3. Law of indipendent assortment 

  • Genes Assort independently

5. Monohybrid Cross 

Digram : Monohybrid Cross 
Digram link below 👇 

Cross :TT × tt

Results : 
  • Phenotypic ratio - 3:1
  • Genotypic ratio - 1:2:1

6. Dihybrid Cross

Digram: Dihybrid Cross 

Cross :Two traits 

Result : 
  • Ratio - 9:3:31
  • Proves independent assortment 

7. Deviations from Mendel 

  1. Incomplete Dominance 
  • Intermediate phenotype
Example: Red + white = pink

     2. Codominance 
  • Both alleles Express
Example : ABO blood group 

    3. Multiple Alleles 
  • More then 2 alleles 
Example : Blood Group 

8. Chromosomal Theory 

  • Proposed by Sutton and Boveri
  • Genes location on Chromosomes
  • Meiosis explains Inheritance 

9. Linkage and Recombination

https://t.me/padhohamesha/76 

Linkage - Genes inherited together 

Recombination - New gene combination 

Occurs in prophase l

10. Sex determination 


Male - XY
Female - XX

Father decide sex

11. Mutation 

  • Sudden change in DNA
  • Types : Point mutations 
  • Chromosomal mutation
  • Example : sickle cell anemia

12. Genetic Disorder

  • Mendelian disorder

  1. Haemophilia 
  2. Thalassemia
  3. Phenylketonuria 
  • Chromosomal disorder
  1. Down syndrome (Trisomy 21)
  2. Klinefelter syndrome (xxy)

Neet Important question 

  • Mendel law 💯 
  • Monohybrid and Dihybrid ratio
  • Incomplete Dominance vs codominance 
  • Blood group inheritance 
  • Chromosomal Theory 
  • Linkage and Recombination 
  • Sex determination 
  • Genetic Disorder 
4-5 Questions Guarented 💯











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