Class 10 Science Chapter 9 Heredity and Evolution Notes

Greetings to all, Today we are going to upload the Class 10 Science Chapter 9 Heredity and Evolution Notes PDF for the assistance of all the students as well as teachers. CBSE Class 10 students can make their Science exam preparations easier and more effective with the assistance of revision notes provided by Pdf file Notes for CBSE Class 10 Science Chapter 9 – Heredity and Evolution are obtainable here. These notes are entirely according to the revised CBSE syllabus. All the topics and concepts have been discussed briefly and clearly. Students can direct to these notes for quick revision before the exam to give an edge to their practice level and increase their final score.

Heredity And Evolution Short Summary

Heredity and evolution are the transmissions of characters from parents to their children. An inherited trait that children get from their parents is a genetically determined feature that makes humans distinguishable from person to person. One of the most common examples of heredity and evolution is the free or attached ears, which we can see around us in humans.

In the same way, we can find out other examples in the human body and animals, and this chapter is all about the changes that took place and how. Today we will be providing students with in-depth knowledge of heredity and evolution by showing them the importance of different types of reproductions, genes, traits, and many more.

Detailed Table of the Chapter 9 Notes – Heredity And Evolution Class 10 PDF

Sr. No. Particular Description
1. Class 10th
2. Chapter 9
3. Title of the chapter Heredity and Evolution
4. Board CBSE
5 subject Science

Heredity and Evolution Class 10 Handwritten Notes PDF

Sexual reproduction

  1. The mode of reproduction involves two individuals; one male and one female.
  2. They produce sex cells or gametes which fuse to form a new organism.


  1. Gene is the functional unit of heredity.
  2. Every gene controls one or several particular characteristic features in living organisms.

The process by which the features of an organism are passed on from one generation to another is called heredity.

  • The process is done by genes, which define the characters in the organism.

Mendel’s work

  1. Gregor Johann Mendel, known as the ‘Father of Genetics’, was an Austrian Monk who worked on pea plants to understand the concept of heredity.
  2. His work laid the foundation of modern genetics.
  3. He made three basic laws of inheritance – The Law of Dominance, The Law of Segregation, and The Law of Independent Assortment.

Dominant traits

  • In Mendel’s experiment, we see that the tall trait in pea plants tends to express more than the short trait.
  • Therefore, the tall trait of the plant is said to be dominant over the short trait.

Recessive traits
A trait that is not expressed in the presence of a dominant allele is known as recessive.

  • So, recessive character/trait is present in an organism but cannot be seen if a dominant allele exists.

Monohybrid cross

  1. When only one character is considered while crossing two organisms, then such a cross is known as a monohybrid cross.
  2. The ratio of characters, arising out of this cross, at F2 generation is called the monohybrid ratio.
  3. E.g., If a tall plant (TT) is crossed with a dwarf plant (tt), we get 3 tall:1 short plants at the end of the F2 generation.
  4. So, 3:1 is a monohybrid ratio.
  5. Here, the height of the plant is considered at a time.

Dihybrid cross

  1. When two characters are considered while crossing two organisms, then such a cross is known as a dihybrid cross.
  2. The ratio of characters, arising out of this cross, at F2 generation is called the dihybrid ratio.
  3. E.g., If a plant with round and green pea is crossed with a plant with wrinkled and yellow pea,
  4. The first-generation plants would all have round and green pea.
  5. On crossing the same for an F2 generation, we would observe four combinations of characters in the ratio of 9:3:3:1.
  6. Thus, 9:3:3:1 is the dihybrid ratio.

In Biology, inheritance pertains to the transfer of traits from one generation to another.
Laws of Mendel
The Law of Dominance says that a gene has two contrasting alleles and one always expresses itself in the organism.
It is called the dominant gene and it expresses in any possible combination.
Law of Segregation says that traits get segregated completely during the formation of gametes without any mixing of alleles.
Law of Independent Assortment says that the traits can segregate independently of different characters during gamete formation.

Sex determination
  1. The process of determining the sex of an individual, based on the composition of the genetic material is called sex determination.
  2. In different animals, the sex of an embryo is determined by different factors.
  3. In humans, sex determination happens based on the presence or absence of the Y chromosome.
  4. XX is female and XY is male
  5. An ovum always contains an X chromosome.
  6. An ovum, upon fusion with Y containing sperm, gives rise to a male child and upon fusion with X containing sperm gives rise to a girl child.

Traits are characteristic features of an organism, manifested in a physical form that is visible or in a physiological aspect of the organism.

Acquired characters
  1. The traits that are acquired by an organism throughout its lifetime are termed acquired characters.
  2. These characters may or may not get transferred to the next generation.

Inherited characters

  1. The traits that are inherited from the parents are called inherited characters.
  2. These traits always get transferred to the next generation, but depending on the dominance or recessiveness it may or may not be expressed.
  3. Examples are height, skin color, and eye color.

Genetic variations
The differences in the DNA sequences among every organism leading to the diverse gene pool are called genetic variations. These differences lead to different/varied physical characters or biochemical pathways.
Natural selection

  1. It is the phenomenon by which a favorable trait in a population of a species is selected.
  2. Changing natural conditions exert equal pressure on all the existing species.
  3. The species/organisms which are better adapted to the changing conditions survive and reproduce i.e. selected by nature and species/organisms which cannot adapt perish i.e. rejected by nature.

Class 10 Biology Heredity and Evolution Notes PDF NCERT Solutions

Question 1.
What are the different ways in which individuals with a particular trait may increase in a population?
Different ways in which individuals with a particular trait may increase in a population are as follow :

  • If it gives the benefit of survival through natural selection.
  • Due to a sudden increase in a particular trait in a population, i.e., by genetic drift.

Question 2.
Why are traits acquired during the lifetime of an individual not inherited?
The traits acquired during the lifetime are changes in the non-reproductive cells of the organisms and are not capable of being passed on to the next generation.
Question 3.
What factors would lead to the rise of a new species?
The factors that would lead to the rise of a new species are the following :

  1. The geographical isolation of a population is caused by various types of barriers (such as mountain ranges, rivers, and the sea). The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of the population.
  2. Genetic drift is caused by drastic changes in the frequencies of particular genes by chance alone.
  3. Variations are caused in individuals due to natural selection.

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