CBSE Class 10 Science Revision Notes Chapter 9

CBSE Class 10 Science Revision Notes Chapter 9 – Heredity and Evolution:

Class 10 is one of the crucial standards in the educational journey of a student. It is extremely crucial for students to study and prepare for their board examinations with dedication and focus. Students have to cover all the subjects with thorough practice and revision. One of the important subjects, Science, does require extra guidance and time to revise the course entirely. Students find it challenging to complete the course in one go. Hence, Extramarks has come up with a comprehensive way to help students thoroughly revise and practise all the chapters. 

Students can now find CBSE Class 10 Science Revision Notes Chapter 9 on Extramarks. The experts have prepared these revision notes after following CBSE and NCERT guidelines. Apart from these revision notes, students can also have access to Formula, Important Question, CBSE Sample Papers, CBSE Previous Year Question Papers, CBSE Extra Questions, etc.

CBSE Class 10 Science Revision Notes for the Year 2022-23

Sign Up and get complete access to CBSE Class 10 Science Chapterwise Revision Notes for the following chapters:

CBSE Class 10 Science Revision Notes
Sr No. Chapters
1 Chapter 1 – Chemical Reactions and Equations
2 Chapter 2 – Acids, Bases and Salts
3 Chapter 3 – Metals and Non-metals
4 Chapter 4 – Carbon and Its Compounds
5 Chapter 5 – Periodic Classification of Elements
6 Chapter 6 – Life Processes
7 Chapter 7 – Control and Coordination
8 Chapter 8 – How do Organisms Reproduce?
9 Chapter 9 – Heredity and Evolution
10 Chapter 10 – Light Reflection and Refraction
11 Chapter 11 – Human Eye and Colourful World
12 Chapter 12 – Electricity
13 Chapter 13 – Magnetic Effects of Electric Current
14 Chapter 14 – Sources of Energy
15 Chapter 15 – Our Environment
16 Chapter 16 – Management of Natural Resources

CBSE Class 10 Science Chapter 9 – Heredity and Evolution Revision Notes

Access Class 10 Science Chapter 9 – Heredity and Evolution:

Accumulation of Variation During Reproduction:

  • Due to the process of DNA copying during reproduction, children resemble their parents but also differ from them in various ways.
  • These differences are visible in asexual reproduction, as in plants, but there are more variations and diversity in sexual reproduction, which involves the fusion of two different gametes. 
  • This results in the variations seen in each generation.
  • Individuals may benefit or suffer from these differences, and they may or may not be able to adapt to the shifting environmental conditions. The bacteria that can endure higher temperatures, for instance, would endure the heat waves.
  • Because of environmental factors, these variations accumulate over generations in the evolutionary process, leading to the formation of new species and are equally important for their survival.



Traits are passed down through generations through heredity. Genes are functional units of heredity that pass down traits from parents to offspring. This is in charge of maintaining generational variations and thus the evolution of species over time.

Inherited Traits:

  • Traits are characteristics that are inherited from one’s parents, such as eye colour or skin colour in humans. If both parents have brown and black eyes, the offspring may inherit either brown or black eyes or a combination of the two. This depends on the set of genes responsible for that trait. 
  • The traits that are inherited in this manner are known as inherited traits, and they are the source of population variation, although everyone has a similar basic feature.

Rules for the Inheritance of Traits- Mendel’s Contributions:

  • Because both the mother and the father contribute equally to the features a kid develops, there are specific rules for the inheritance of these traits in humans.
  • Mendel discovered throughout his pea experiment that certain factors known as genes controlled the traits.
  • Alleles are pairs of genes that contribute to a particular phenotype.
  • Dominant traits are those that can be observed and express themselves in every imaginable way in an organism.
  • Recessive refers to a trait that does not develop when a dominant allele is present.
  • Phenotype refers to the morphological expression of a single trait. For instance, consider the plant’s tall or short, rounded or wrinkled seeds.
  • The genotype is the genetic makeup or the pair of alleles for a particular trait. Example: Tt or t tot TT.

How do These Traits Get Expressed?

  • The proteins are created by the DNA in the cell.
  • In many of the biochemical processes that result in the development of a trait, the proteins that are subsequently synthesised are crucial, and they are regulated by particular enzymes.
  • The traits must exist individually if they are to be acquired from each parent independently.
  • Each cell has two sets of chromosomes, one from each parent, and as a result, each gene set is present as a distinct, independent unit.
  • The number of chromosomes and hence the DNA tend to be restored when these two germ cells come together.

Sex Determination:

  • The methods used by various species to determine sex vary significantly.
  • It can depend on the temperature at which the fertilised eggs are stored, as is the case with several reptiles.
  • A pair of 22 chromosomes typically consists of one chromosome from each parent. Most traits are generally determined by these.
  • In humans, men have XY chromosomes and women have XX chromosomes.
  • Which sex chromosome pair is inherited from the father determines the child’s sex.
  • In the event that it is X, the pair becomes XX and the child is a girl; in the event that Y is inherited, the pair becomes XY and the child is a boy.


  • A population’s heritable features can change over many generations in a way that can be observed as evolution. As a result of these changes, new species may develop or existing species may alter themselves to better adapt to their surroundings.
  • New species eventually evolve as a result of evolution.
  • Natural selection describes the selection of traits in a population that increase its chances of survival and help it adapt to its surroundings.
  • Mendel was the one who put forth the theory of how qualities are passed down through families.

Acquired and Inherited Traits:

  • An organism does not pass on any traits it develops over its lifespan as a result of environmental factors to its offspring. These characteristics are known as acquired attributes. As an illustration, consider a person’s speech pattern or skill set. Since these modifications do not impact germ cells, they cannot be passed down from one generation to the next.
  • An inherited trait is any characteristic that is genetically inherited or passed down from one generation to the next. The colour of your eyes or skin, for instance.


  • It is a process whereby a new species is created from an existing one as a result of several evolutionary pressures, including genetic drift, population isolation, natural selection, etc. Speciation creates diversity in the ecosystem, and diversity creates the opportunity for evolution. 
  • Genetic Drift: The populations undergo a change in their genes for some traits that are specific to that species due to unprecedented reasons. As a result, they are moved to another population that already exists. 
  • Gene Flow: The transfer of genes from one group to another is referred to as gene flow. Migration or the introduction of organisms to a new population are the causes of this. 
  • Natural Selection: It is the process by which a desirable trait is chosen in a population of a species. 

Evolution and Classification:

  • The traits or specifics of the look or behaviour that are observed for a given form or function constitute the similarities across organisms that enable them to be grouped together.
  • The classification procedure also considers whether the nucleated cells are multicellular or single-celled. This enables the evolution process to produce a hierarchy that aids in the categorisation of groups.
  • Therefore, the closer two species are related, the more traits they have in common.

Tracing Evolutionary Relationships:

  • Organs that are homologous are those whose structures and functions are comparable. Bird wings and mammal forelimbs share structural similarities but have been altered for various purposes.
  • Organs that operate similarly yet have different structures and origins are said to be analogous. Bat wings, bird wings, and insect wings are all utilised for flight, although they are all structurally extremely different.


  • The preserved remains of extinct creatures or plants that died millions of years ago are known as fossils.
  • We can learn more about these animals’ physiology and even anatomy because of their fossils.
  • When an organism dies, it is buried in mud and silt.
  • Petrification is the process by which minerals enter decaying bones and replace the contents cell by cell.
  • The cast of the animal is left behind if bones fully disintegrate.

Evolution by Stages:

  • Evolution is a gradual process that does not take place instantly.
  • The evolution of practically every species we see today has gone through multiple stages.
  • Complexities develop gradually rather than suddenly, and at some points, they may only be of limited use.
  • Evolution by stages is the name given to this progressive evolutionary process.

Evolution Should Not be Equated With Progress:

  • The emergence of a new species does not mean that the old one has vanished or that it is less useful than the new one. It suggests that the alterations in the environment are what led to the evolution of the new species.
  • As a result, evolution cannot be observed for advancement. Every species adapts to its environment and diversifies in order to reproduce and live.
  • Despite being the most advanced species, humans are still simply one of many species that have evolved.

Human Evolution:

  • We know that humans are members of the primate family.
  • Today’s humans share a very strong genetic affinity with chimpanzees and other animals.
  • A more comprehensive picture of human evolution has emerged, even though the precise evolutionary path that separated humans from primates remains a mystery.
  • Dryopithecus, Ramapithecus, Australopithecus, Homo erectus, Homo sapiens neanderthalensis, Cro-Magnon man, and lastly, the Homo sapiens, are some of the predecessors of modern humans.

Heredity And Evolution Notes Science Chapter 9

Topic Covered in Heredity and Evolution Class 10 Notes:

  • Modes of Reproduction
  • Genes
  • Heredity
  • Inherited Traits
  • Rules for the Inheritance of Traits- Mendel’s Contributions:
  • How do These Traits Get Expressed?
  • Sex Determination
  • Evolution
  • Acquired and Inherited Traits
  • Speciation
  • Evolution and Classification
  • Tracing Evolutionary Relationships
  • Fossils
  • Evolution by Stages
  • Evolution Should Not be Equated With Progress
  • Human Evolution

Things to Keep in Mind for Chapter 9 Science Class 10 Notes:

All the topics covered in the notes must be carefully studied by students before exams. Students must also keep a check on the time needed to complete each topic properly so that time can be distributed accordingly for each of the topics. Apart from the above-mentioned notes, students must also know about the three laws given by Gregor Johann Mendel which are:

  • Law of Dominance
  • Law of Segregation
  • Law of Independent Assortment

Notes of Chapter Heredity and Evolution Class 10th:



Class 10 Science Notes Chapter 9 by Extramarks is prepared by the leading experts in the respective area of knowledge and hence there is a minimum chance of error and mistakes. These notes when properly revised alongside solving questions prepare the student best for the given examination. Students can also have access to the notes through the download feature for offline use.

FAQs (Frequently Asked Questions)

1. What is evolution?

The development of plants, animals, etc over many thousand years from simple forms to complex advanced forms.


2. What does the Law of Segregation state?

The law of segregation states that each individual that is a diploid has a pair of alleles (copies) for a particular trait.

3. What is meant by natural selection?

The process through which organisms adapt and change themselves in huge populations is known as natural selection.