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

Download NCERT Notes for Class 10 Science Chapter 8 PDF

This chapter helps to understand how traits are passed from parents to offspring and why we look similar or different. Students can download the NCERT notes for class 10 Science chapter 8 PDF to do offline study. Every time studying the chapter from the textbook takes a lot of time. That’s why the notes are the best study material. The NCERT Notes for Class 10 Science are written in a simple way to make revision faster and easier.

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Heredity Class 10 Notes

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. Heredity Class 10 Notes 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.

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 of 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.

Important Definitions - Class 10 Science Chapter 8 Notes

Given below are a few important definitions from the heredity chapter. Understanding these basics will help students revise quickly and solve exam questions with ease.

• 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

Points to Remember - Class 10 Science Chapter 8 Notes

This section highlights the main points to remember from the heredity chapter. Going through these points will help in quick revision and better understanding of the concepts.

• 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.

• Traits are controlled by genes present on chromosomes.

• Each offspring inherits one set of genes from the mother and one set from the father.

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 up in past years from the chapter are given below. Students can also check the Class 10 Science Chapter 8 Notes for a better understanding.

Question 1. Changes accumulated and cause organisms to 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: