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heredity and evolution class 10 notes

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We and our parents have the resemblance towards our generation and that is the same case with animals which we’re going to explain in chapter 9 Heredity and Evolution of class 10th.

Have you ever thought that a dog always gives birth to a dog and a banyan tree seed only produces a banyan tree and why certain species can live in places like Antarctica, why kangaroos are restricted to Australia only. So, students here are the answer to some of your questions related to Heredity and Evolution class 10th level.

In this blog, we are going to explain all the basic terms related to Heredity and Evolution in brief.


The process by which the character is being passed from first generation to another generation is called heredity.

Terms Related to Heredity:

1. Sexual reproduction: the process of reproduction in which two parents are involved. It leads to variations in the population because parents involve two different families.

2. Asexual reproduction: the process of reproduction in which single parent is involved and the offspring’s (child) are exact copies of their parents.

Accumulation of variation during sexual reproduction

Sexual reproduction involves two parents, in case of humans from two different families. This mode of reproduction involves DNA fusion which leads to accumulation of variation, but in asexual reproduction single parent is involved, DNA comes from that single parent only which does not involve any kind of variation.

Historical Aspects of Heredity

Rules of inheritance Mendel’s contribution

The rules of inheritance especially in humans include both mother and father contribution to the reproduction, both contribute equal amounts of DNA. Although traits are influenced by many of the things Mendel’s has done the contribution in this field the century ago because of his work he secured a special place in the field of genetics So, students must study his experiment which is very important in Heredity and Evolution class 10.

Mendel used Pisum sativum (pea) for his experiment; he studied seven pairs of contrasting traits in this plant. He has chosen the characters, which are easily differentiable on seeing. He was the first who has incorporated math into the field of biology (which made his work stand on a different level). He had done his experiment over 7 years and then checked the percentage of persistence of character in his generations of pea plants.

heredity and evolution class 10
The characters which as chosen by Mendel for his experiment

In his experiment, he took one character first that is “height”, he selected a completely tall plant as male parent and dwarf (short) plant as the female parent. He made a pollination between then he observed all the offspring in the f1 generation were tall (that means only one of the parental traits has been expressed).

Then for the next generation he has done the self-pollination between the first generation offspring’s then he saw 3/4th of the plants were tall but 1/4th of them were small that means one of the characters which was not expressed in the first generation was not expressed now that character has expressed itself.

(This cross is known as monohybrid cross because in this only one character is studied)

class 10 heredity and evolution
Genes, they are known as unit of inheritance

Genotype is known as the genotype and phenotype is known as the physical appearance

Genotype ratio in monohybrid cross for f1 (first generation) - 1:1:1:1

Phenotype ratio in monohybrid cross for f1 (first generation) - 1:1:1:1

For second generation phenotype ratio: 1:2:1

For second generation genotype ratio: 3:1

There are cross in which more than two characters were considered by Mendel’s then these are known as dihybrid cross.

heredity and evolution class 10 ncert solutions

This cross is very important in 10th class, chapter 9 heredity and evolution.

This cross is very important in 10th class, chapter 9 heredity and evolution.

Mendel’s Law

(i) Law of dominance: It states that in a pair of alleles only one pair is dominant over the other.

(ii) Law of segregation It states that traits get segregated completely during the formation of gametes.

(iii) Law of assortment: It states that traits get independently assorted during the formation of gametes

Sex determination

a) It is the process of determining the sex by the genetic constitution of an individual.

b) In human beings this process is known as XY sex determination method.

c) The male consists of XY pair of sex chromosome.

d) The female contains XX pair of sex chromosome.

e) The sperm (male) are of two types X and Y.

f) The ovum is only of one type X.

g) The ovum or egg (female) on fusion with X type of sperm leads to the formation of the female and with Y chromosome leads to the formation of male.

So, students as we have seen the historical aspect of genetics, but other than this there are many more things which also need to be considered from the notes point of view of Heredity and Evolution class 10th

When Mendel published his work there was one more thing which was so popular in that era and that was “Evolution”, now let’s begin our journey on “evolution” and this is another interesting and important concept of Heredity and Evolution class 10th.


Genetic variation

The difference at the molecular level (DNA) that leads to diversity in the gene pool that is known as genetic variation. These differences lead to different molecular and physical characteristics in the individual.

Natural selection

1) This is one of the most renowned phenomena in the field of evolution.

2) “Charles Darwin” has given the concept of evolution. He is known as the father of evolution.

3) He has travelled across the world through the ship H.M.S beagle and then he put forward the concept of evolution.

4) In his book “on origin of species” he has given the concept of evolution in detail.

5) According to this the species which have the best tendency to cope up with the changing environment condition are best suitable for the environment and can grow to more generations.


It is the formation of new species from existing new species due to many evolutionary forces like genetic drift, gene migration, natural selection, and genetic flow etc.

Gene flow

Gene flow is the transfer of genes from one generation to another generation.

Genetic drift

Genetic drift is the change in gene population (allele frequency) of an existing allele in the small population.


A population is a community or group of organisms, animals or plants that reproduce and produce viable offspring.


Evolution is the change in species characters over many generations. The modern world of today’s era in all respects is a true story of “evolution”. Due to this process, the individuals which develop are better adapted for the new developed condition of changing environment which comes under chapter 9 Heredity and Evolution of class 10th.

Confirmation of evolution


a. They are very important pieces as evidence of evolution.

b. Animals die and are buried over generations in the sediments where soft tissue dissolves as a mineral in the soil and their hard bones remain in the soil over which sedimentation occurs this process is known as petrification.

c. Fossils give a proof of organism of that era for ex dinosaur, archaeopteryx.

heredity and evolution class 10 important questions

Evolutionary relationships

The Evolutionary relationships of different organisms can be studied by studying the chain of their evolutionary relationships in chapter 9 Heredity and Evolution.

Homologous organs

a. These are those organs which have similar structure and different functions.

b. Wings of birds and forelimbs of mammals. They have similar structures, but they are suited for different functions.

c. These structures get developed due to different adaptive needs.

heredity and evolution notes

Analogous structure

These are the structures of organisms which have different structures, but similar functions.

Homologous organs

A. Wings of bats and birds are structurally different but have similar functions.

B. Leaves of cactus (opuntia) and peepal, both perform the function of photosynthesis, but leaves of cactus (opuntia) are modified into leaves.

Evolution by stage

(i) Evolution is a complex process; it is not something which just happens overnight.

(ii) The world which we see today is the true story of evolution, which is because evolution has occurred over stages.

(iii) Complexities don't evolve overnight; it took a lot of years to come at such a high level of development.

Artificial selection

When a single species develops into different species of the same type, it is known as artificial selection.

E.g. a single ancestor of the cabbage family gives rise to different species of the cabbage family.

heredity and evolution class 10 questions
(Artificial selection in cabbage)

Molecular phylogeny

• The evolutionary relationship study of different organisms is known as molecular phylogeny.

• The evolutionary relationship study of different organisms is known as molecular phylogeny.

Human evolution

heredity and evolution class 10 important questions

1. Humans are known to belong to primates.

2. This concept of belongingness with primate was first said by Darwin is his theory of evolution.

3. The complete resemblances are still under study.

4. Some of the ancestors of humans are discovered from different eras, these are Ramapatheciens, Australopithecines, Homo nidherlandathcions, Homo sapiens.

5. Human evolution traced to Africa and moved into different parts of the world.

We firmly believe that you’ve understood the basics of Heredity and Evolution to the fullest.

Some Important Questions Related to Heredity and Evolution Lesson for 10th Class.

Questions 1. Explain by giving examples of homogenous and homogenous organs?

Answer: Those organs which are similar in infrastructure but have different functions, are called homogenous organs. For example, birds, water - landmarks, others have four legs but their functions are different. On the contrary, those organs which have the same basic structure but work the same in different organisms, are called identical organs. Examples - bats and bird feathers. The wings of bats are formed by the spreading of the skin between the long fingers, but the bird's wings spread from the skin of the entire forearm.

Question 2. How to determine the sex of a child in human beings?

Answer: The sex chromosome determines the sex of the child. In humans, chromosomes determine. A human has 23 pairs of chromosomes. Of which 1 pair belongs to the sex chromosome, the females have the sex chromosomes (xx). But men have sex chromosomes (xy). All children have "x" chromosomes from their mother. But any "X" or "Y" from the father. Thus the chromosome of the father decides whether the child is a son or a daughter.

Question 3. What are fossils? What do they indicate about the process of bio-development?

Answer: The remains of dead organisms, the signs on the rocks or the mold and the imprint of the body which were alive thousands of years ago, such untouched remains are called fossils. These fossils tell us many things about bio-development process like which fossils are new & which is old and which species have become extinct. These fossil evolution can also describe the properties of the various forms and layers of land.

Question 4. What is the importance of fossils in establishing the evolving relationships?

Answer: Fossils are the remains of those creatures which are now extinct. When we compare the structure of fossils of those organisms with the present ones, we get to know how the organisms evolved and also explain the fossil evolutionary order system.

Question 5. What are genes?

Answer: Genes are the smallest genetic units that are the part of the DNA present in chromosomes and transfer traits from one generation to another.

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