CBSE Grade-12 Biology | 4. Principles of Inheritance and Variation by Pavan | Learn Smarter
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4. Principles of Inheritance and Variation

The principles of inheritance and variation are explored through Mendel's groundbreaking work on pea plants, establishing foundational laws such as the Law of Dominance and the Law of Segregation. The chapter delves into genetic mechanisms including monohybrid and dihybrid crosses, incomplete dominance, and co-dominance, while also discussing the chromosomal theory of inheritance. It further addresses the complexities of genetic disorders and sex determination.

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Sections

  • 4

    Principles Of Inheritance And Variation

    This section explores the fundamental principles of inheritance as established by Gregor Mendel, including concepts such as dominant and recessive traits, genetic disorders, and the significance of alleles.

    Learning Practice

  • 4.1

    Mendel’s Laws Of Inheritance

    Mendel's work established foundational principles of genetics through his experiments with pea plants, leading to the development of the laws of inheritance regarding dominant and recessive traits.

    Learning Practice

  • 4.2

    Inheritance Of One Gene

    This section discusses the inheritance patterns established by Mendel through his monohybrid crosses, focusing on the principles of dominance and segregation.

    Learning Practice

  • 4.2.1

    Law Of Dominance

    The Law of Dominance states that in a pair of contrasting traits, one trait (dominant) will obscure the expression of the other (recessive) in the phenotype of the offspring.

    Learning Practice

  • 4.2.2

    Law Of Segregation

    The Law of Segregation states that allele pairs segregate during gamete formation, ensuring that each gamete receives only one allele from each pair.

    Learning Practice

  • 4.2.2.1

    Incomplete Dominance

    Incomplete dominance is a form of inheritance where the phenotype of the offspring is a blend of the phenotypes of the parental traits, exemplified by flower color in snapdragons.

    Learning Practice

  • 4.2.2.2

    Co-Dominance

    This section describes the concept of co-dominance and how it differs from complete dominance and incomplete dominance in genetics.

    Learning Practice

  • 4.3

    Inheritance Of Two Genes

    This section explores the inheritance patterns involving two genes, emphasizing the development of Mendel's laws of inheritance and the concept of independent assortment.

    Learning Practice

  • 4.3.1

    Law Of Independent Assortment

    The Law of Independent Assortment states that the segregation of one pair of alleles occurs independently of another pair during the formation of gametes.

    Learning

  • 4.3.2

    Chromosomal Theory Of Inheritance

    The Chromosomal Theory of Inheritance connects the behavior of chromosomes during meiosis with Mendel's laws of inheritance, emphasizing that genes are located on chromosomes.

    Learning Practice

  • 4.3.3

    Linkage And Recombination

    Linkage and recombination are crucial concepts in genetics that explain how genes located on the same chromosome can influence inheritance patterns and why some traits appear to be inherited together.

    Learning Practice

  • 4.4

    Polygenic Inheritance

    Polygenic inheritance involves traits that are controlled by multiple genes and exhibit continuous variation, as seen in human traits like height and skin color.

    Learning Practice

  • 4.5

    Pleiotropy

    Pleiotropy is a genetic phenomenon where a single gene influences multiple phenotypic traits.

    Learning Practice

  • 4.6

    Sex Determination

    This section explores the mechanisms of sex determination in various organisms, focusing on genetic and chromosomal bases.

    Learning Practice

  • 4.6.1

    Sex Determination In Humans

    Sex determination in humans is primarily governed by the XY chromosome system, which involves the genetic contributions from both parents.

    Learning Practice

  • 4.6.2

    Sex Determination In Honey Bee

    Honey bee sex determination is based on chromosome sets: fertilized eggs develop into females, while unfertilized eggs develop into males.

    Learning Practice

  • 4.7

    Mutation

    Mutation involves changes in DNA sequences that can affect an organism's genotype and phenotype, contributing to genetic variation.

    Learning Practice

  • 4.8

    Genetic Disorders

    Genetic disorders arise from mutations, alterations in genes, and chromosomal abnormalities, often studied through pedigree analysis.

    Learning Practice

  • 4.8.1

    Pedigree Analysis

    Pedigree analysis is a method used to trace the inheritance of traits or disorders across generations within a family.

    Learning Practice

  • 4.8.2

    Mendelian Disorders

    Mendelian disorders stem from single gene mutations that follow traditional inheritance patterns.

    Learning Practice

  • 4.8.3

    Chromosomal Disorders

    Chromosomal disorders result from abnormalities in chromosome number or structure, leading to various genetic conditions.

    Learning Practice

References

NCERT Study Material

Class Notes

Memorization

What we have learnt

  • Inheritance is the process ...
  • Mendel's experiments laid t...
  • Genetic disorders can arise...

Final Test

Revision Tests