Heredity Class 10 Notes Science Chapter 9

 Heredity Class 10 Notes CBSE Science Chapter 9

NCERT CBSE Class 10 Revision Notes Science includes Notes from Chapter 9. Heredity subjects from the textbook are included in the revision notes for class.
This chapter note includes topic- or concept-wise explanations for all of the topics provided in the book, such as genetic engineering, heredity, genes, characteristics, variations, law inheritance, and sex determination.
Class 10th Science Notes will help students comprehend the ideas, concepts, and themes covered in all chapters of the NCERT Textbook of Physics.

Heredity Introduction

Heredity Class 10 Notes Pdf Chapter 9 Science Notes

All living organisms give rise to new individuals (offspring) by a process of reproduction.

The offspring produced as a result is similar to their parent but not identical i.e. they also show some differences.

-The mechanism of transmission of character is called Heredity or Inheritance while the differences seen among individuals is called variations Accumulation of Variation during Reproduction


-The differences in the characters (or traits) among the parents and their offspring, the offspring or the individuals of same specs is called as variation.

- Some amount of variation is produced during asexual reproduction while the number of successful variations are maximized by the process of Sexual Reproduction

Importance of Variation

-Depending on the nature of variation, different individuals of a species can have different advantages. E.g: Bacteria that can withstand heat will survive better in a heat wave.

-Main advantage of variation to a species is that it increases the chances of its survival in a changing environment.


The transmission of characters from parents to offspring is called heredity


Inherited Traits

Acquired Traits

Traits that are received from parents are called Inherited Traits

Traits that are obtained during lifetime are called acquired traits, They cant be passed on to the next These can be passed on to the next generation generation. They don't result in evolution -Eg, Learning a new language, playing tennis etc.

-They occur due to change in DNA.

-No change in DNA is involved.

Inherited traits lead to evolution

Eg. Nose Shape, Hair Colour

Rule of Inheritance of Traits-

Gregor Mendel

- Considered as the "Father of Genetics"

-He was the first Scientist to make a systematic study of patterns of inheritance. -He used pea plants Pisum sativum for his experiments.

Tall Plant Height


Round Wrinkled Gara



Seed Color

Important Terms

Factor/Gene- It is a segment of DNA that determines a particular

character. Genes are represented by letters. A capital letter shows that |

the gene is dominant, and a small one that it is recessive. Alleles - Alternate forms of a gene. Eg, Pea plant height - Tall(T) & Short

(1) Allele

Dominant Allele- A dominant allele expresses itself in the presence or absence of recessive allele. Example - Allele for tallness (T)

Recessive Allele - A recessive allele is able to express itself only in the Genotype-It is the genetic composition of an individual Example TT, TT

absence of a dominant allele. Example - Allele for shortness (1)

or tt

Phenotype - It is the characteristic which is visible in an organism. Example Tall or Short plant height.

Homozygous - An individual having identical alleles. Example TT or t

Heterozygous - An individual having contrasting alleles. Example T

Monohybrid Cross

In monohybrid cross, we consider one pair of contrasting trait.

1. Mendel selected true breeding tall pea plant (TT) and crossed it with Short (tt) plant.

2. The plants formed as a result of the cross represented first

filial or F: generation. 3. All the F: plants obtained were tall

4. Mendel self-pollinated the Fi plants (selfing) and observed that

plants in the Fz generation were 75% tall and 25% Shortie

phenotypic ratio 3:1

Parental Generation.







F: Generation



Phenotype - All tell



Selfing Fi




F: Generation



Tell T



Phenotypic Ratio - 3 Tall1 Shart

Genotypic Ratio-ITT:2 T:1

Dihybrid Cross

In Dihybrid cross. We consider two pairs of contrasting traits. (Seed shape and Seed Colour) Experiment

1) Mendel crossed pea plants bearing Round & Yellow seeds (Rryy) with wrinkled green (rryy) plants having Round and

2) He obtained F1 generation with all pea pla Yellow seeds (Rrvy)

3) On Selfing Fl offspring. Mendel obtained 4 different types of progeny in F2 generation: Round & Yellow, Round and Green, Wrinkled & green and Wrinkled green in the ratio


Parental Generation

Wrinkled & Green


F₁ Generation




Round & Yellow

Selfing Fi Generation







Fs Generation





W 2


Mendel's Laws

Law of Dominanss-

Mendel's Law of dominance states that in a heterozygote, one trait will conceal the presence of another trait.


Toll (TT)

Short (tt)

Tall (T)

Law of Segregation-

When an organism makes gametes, gamete receives just one

gene copy, which is randomly. This is known as the low of Segregation


Tall (T)


Law of Independent Assortment-

Mendel's law of independent assortment that the alleles of two more (or more) different genes get sorted into gametes independently of one another.

Eg. In a dihybrid cross, the shape of seed doesn't depend on the colour of seed.

10 How do traits get expressed?

-Cellular DNA is the information source for making proteins in the cell. A part of DNA that provides information for one particular protein is called o gene for that protein.

- Example

Height of a plant depends upon growth hormone which in turn is controlled by the gene. If the gene is efficient and more growth. hormone is secreted, the plant will grow tall If the gene gets altered and less hormone is secreted, then the plant will remain shart. Thus, genes control characteristics or traits.

Sex Determination

-The process by which sex of a new born individual is determined is called Sex Determination Factors determination Sex Determination


Genetically In humans, genes inherited from parents decide the sex of the offspring

-Environmental cues: In turtles, Alligators, Crocodile, temperature at which fertilized eggs are kept determines sex

-In Snails, individuals can

Change Sex

Sex determination in humans

In humans, sex of the child depends on the father or we can say, the male gamete that fuses with the female gamete Humans possess 23 pairs of chromosomes out of which one pair comprises the sex chromosomes

(XX in females-perfect pair)

(XY in males- Mis-matched pair)

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