NCERT Class 10 Science Chapter 9 Notes Heredity And Evolution- Download PDF Notes

Have you ever wondered why you look like your parents or how new species come to exist? The NCERT Class 10 Science Chapter 8 Notes Heredity help you get these answers in a simple way. These notes cover how traits are passed down, what genes do, and how evolution happens over time. With easy language, neat diagrams, and short points, you can go through NCERT Notes without feeling confused or stressed.

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1. Download NCERT Notes for Class 10 Chapter 8 PDF
2. NCERT Notes for Class 10 Chapter 8
3. Chapter 8 Previous Year Questions and Answers
4. Chapter-Wise NCERT Class 10 Notes Science

These NCERT Notes for Class 10 Science explain Mendel’s experiments, dominant and recessive traits, and Darwin’s ideas in a step-by-step style. There are diagram suggestions and small answer-writing tips added, so students know what to include in exams. Everything follows the NCERT book, so no important topic is missed. These NCERT Notes of Class 10 will help them get your basics clear about heredity and evolution, and give them the confidence to handle related questions easily.

Also read,

• NCERT Solutions for Class 10 Science Chapter 8 Heredity

Download NCERT Notes for Class 10 Chapter 8 PDF

This chapter helps you understand how traits are passed from parents to offspring and why we look similar or different from our family members. The notes are written in a simple way to make revision faster and easier. You can now download the NCERT Class 10 Science Chapter 8 Notes Heredity PDF for clear and quick exam preparation.

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NCERT Notes for Class 10 Chapter 8

It is amazing to think that the colour of your eyes or the shape of your nose is linked to traits passed down for generations. NCERT Class 10 Science Chapter 8 explains Heredity, showing how traits move from parents to children and how species slowly change over time. This chapter also discusses how variations help organisms survive in changing environments. Understanding these ideas builds a strong base for biology and future genetics studies. Heredity explains how traits are passed from parents to their children. Evolution explains how living things change slowly over time. Together, these concepts help us understand the variety of living beings around us and how they adapt to survive.

Accumulation of Variation During Reproduction

Reproduction results in the formation of new individuals that resemble their parents but also possess certain differences, which are known as variations.

• In asexual reproduction, variation is minimal since only a single parent is involved. The progeny will show minor differences arising mainly due to small inaccuracies during DNA copying.
• In sexual reproduction, two parents contribute genetic material, resulting in greater variations. These variations are produced due to the combination of genetic material from both parents.

Over successive generations, the accumulation of these variations supports the survival of individuals better adapted to changing environments. This accumulation is an important factor in the process of evolution.

Heredity

Heredity refers to the transfer of characters and traits from one generation to the next. It ensures the maintenance of the basic structural design of a species while also introducing differences within populations.

Inherited Traits

An inherited trait is any characteristic passed from parents to offspring, such as eye colour or height. A child inherits half of its genetic material from the mother and half from the father. Therefore, each trait is controlled by two copies of genes, one from each parent.

Mendel’s Work and Experiments

Gregor Johann Mendel conducted experiments on garden pea plants to study the pattern of inheritance. For example, when he crossed tall and short pea plants:

• All plants in the first generation (F1) were tall.
• In the second generation (F2), three-fourths were tall and one-fourth were short.
• From this, Mendel concluded that tallness is a dominant trait, while shortness is a recessive trait.
• Mendel further experimented with pairs of traits, such as seed shape and seed colour. He observed that these traits are inherited independently from each other. This observation is known as the Law of Independent Assortment.

Genes and Chromosomes

Genes are sections of DNA which carry information for specific traits. They control the synthesis of proteins in cells, which in turn determine the features of an organism. Genes are located on thread-like structures known as chromosomes present in the cell nucleus.

• Humans have 23 pairs of chromosomes (a total of 46).
• During the formation of germ cells (sperm and eggs), the chromosome number is reduced to half.
• At fertilisation, the normal number of chromosomes is restored.
• This mechanism ensures the stability of hereditary material over generations.

Expression of Traits

Genes guide the formation of specific proteins, which produce hormones or enzymes controlling particular traits. For example, the gene for plant height influences the production of growth hormones. If the gene functions properly, normal growth takes place. If the gene changes, the hormone may be less effective, leading to a shorter plant. Thus, genes directly control the expression of traits.

Sex Determination in Humans

Sex determination refers to the process by which the sex of a child is decided. In humans:

• Females have two X chromosomes (XX).
• Males have one X and one Y chromosome (XY).
• A child always receives an X chromosome from the mother. From the father, the child may receive either an X chromosome (resulting in a girl, XX) or a Y chromosome (resulting in a boy, XY). Hence, the sex of the child is determined by the type of chromosome contributed by the father.

Evolution

Evolution is the gradual process through which living organisms change over time to form new species.

• Variations present in a population help some individuals survive better in a changing environment.
• Natural selection allows favourable variations to be passed on to the next generation.
• Unfavourable variations are gradually removed.
• Over a long time, this leads to the development of new species adapted to their environment. Evidence of evolution can be obtained through the study of fossils, comparative anatomy, and embryology.

Important Definitions

• Heredity: Transfer of traits from parents to offspring
• Variation: Difference between individuals of the same species
• Gene: Unit of inheritance, part of DNA
• Chromosome: A Structure carrying genes in the nucleus
• Dominant trait: Trait expressed with only one gene copy
• Recessive trait: Trait expressed only with two gene copies
• Evolution: Gradual change in living organisms over time
• Natural selection: The Process where the best-suited variations survive

Points to Remember

• Variations arise during reproduction and can be inherited.
• Dominant traits appear in the first generation, while recessive traits reappear in the second.
• Sex is determined genetically in humans by X and Y chromosomes.
• Evolution is supported by scientific evidence.
• These processes ensure both stability and diversity in living organisms.

Subject-Wise NCERT Solutions

• NCERT Solution
• NCERT Solutions for Class 10 Maths
• NCERT Solutions for Class 10 Science

Chapter 8 Previous Year Questions and Answers

Some of the questions which have come in past years from the chapter are given below:

Question 1. Changes accumulated and cause organisms to get divide into sub-populations can be due to

Option 1. Evolution

Option 2. Natural selection

Option 3. Genetic drift

Option 4. (1), (2) and (3)

Answer :

Speciation is derived from evolution. Over the generations, the genetic drift accumulates different changes in each subpopulation. Also, natural selection may operate differently in these geographic locations.

Hence, the correct options are (4) (1), (2) and (3)

Question 2. Speciation is

Option 1. Origin of the new population

Option 2. Origin of a new individual

Option 3. Origin of existing species

Option 4. Origin of new species

Answer :

The origin of new species from the existing ones is referred to as Speciation.

Hence, the correct option is (4) Origin of new species

Question 3.

Read the following statement and select the correct option

Humans have travelled back and forth to

1. separate from each other

2. Mix with each other

3. Live their best lives

Option 1. 2, 3

Option 2. 1 , 2 , 3

Option 3. Only 1

Option 4. Only 2

Answer :

Humans travelled forward and backwards, sometimes separating and sometimes coming back to mix. Like all other species on the planet, they had come into being as an accident of evolution and were trying to live their lives the best they could.

Hence, the correct option is (2) 1 , 2 , 3

Chapter-Wise NCERT Class 10 Notes Science

Given below are the chapter-wise links of class 10 notes: