CBSE Class 10 Science Revision Notes Chapter 8 Heredity 2026–27

Heredity explains how traits pass from parents to offspring through genes present on chromosomes. In CBSE Class 10 Science Chapter 8, students study variation, inherited traits, Mendel’s experiments and sex determination in human beings.

Heredity explains why offspring look similar to their parents, yet show small differences. These differences appear because reproduction passes inherited traits from one generation to the next with some variation.

Use these CBSE Class 10 Science Revision Notes Chapter 8 for the 2026–27 academic year to revise variation, dominant and recessive traits, Mendel’s experiments, genes, chromosomes and sex determination. Focus on inheritance tables, trait ratios and the role of X and Y chromosomes.

Key Takeaways

• Variation: Differences produced during reproduction may help individuals survive changing conditions.
• Heredity: Traits are inherited through genes, which are sections of DNA.
• Mendel’s experiments: A single copy of a dominant trait can express itself in the offspring.
• Sex determination: In humans, the father’s X or Y chromosome determines the sex of the child.

Struggling with Mendel’s crosses, dominant-recessive traits and sex determination diagrams?
Access interactive practice, live doubt-solving sessions and complete NCERT-based support on the Extramarks Learning App. Sign Up Free

CBSE Class 10 Science Revision Notes Chapter 8 on Heredity: Chapter Overview

Heredity is the passing of traits from parents to offspring. It explains why children have the same basic body design as their parents.

Reproduction creates similar individuals, but not exact copies. These subtle differences accumulate over generations.

Important Topics in CBSE Notes Class 10 Science Chapter 8 Heredity

Class 10 Science Chapter 8 Notes focus on how traits are created, expressed and inherited. Mendel’s experiments help explain these inheritance patterns.

This chapter needs clear understanding of trait symbols. Tables make Mendel’s crosses easier to revise.

Heredity Class 10 Notes: Accumulation of Variation During Reproduction

Variation means differences among individuals of the same species. These differences can arise during reproduction and may be inherited.

In asexual reproduction, variations are fewer because one parent produces offspring. In sexual reproduction, more variation appears because DNA comes from two parents.

Variation in Asexual and Sexual Reproduction

If one bacterium divides into two and both divide again, the new bacteria are very similar. Only small differences arise due to minor DNA copying changes.

In sexual reproduction, offspring inherit traits from both parents. This creates greater diversity among individuals.

How Variation Helps Survival of a Species

Environmental conditions can change. Some variations may help individuals survive better in changed conditions.

Selection of useful variants by environmental factors forms the basis for evolutionary processes. The chapter connects variation with survival of species.

Class 10 Science Chapter 8 Notes on Inherited Traits

Inherited traits are characteristics passed from parents to offspring. Human populations show many such variations.

Examples include free and attached earlobes. Some people have free earlobes, while others have earlobes attached to the side of the head.

Inherited Traits and Examples from Human Populations

A child inherits genetic material from both father and mother. This means each trait can be influenced by paternal and maternal DNA.

Genes, DNA and Trait Expression in Heredity Notes

DNA is the information source for making proteins in the cell. A section of DNA that provides information for one protein is called a gene.

Genes control traits through proteins. For example, plant height can depend on a hormone linked with growth.

If the gene makes an efficient enzyme, more growth hormone may be produced. The plant becomes tall.

If the gene makes a less efficient enzyme, less hormone may be produced. The plant becomes short.

Mendel’s Experiments in CBSE Class 10 Science Revision Notes Chapter 8

Mendel studied inheritance using garden pea plants. He used contrasting visible characters such as tall or short plants and round or wrinkled seeds.

Mendel counted the number of plants showing each trait. This helped him frame the rules of inheritance.

Monohybrid Cross and Dominant-Recessive Traits

In a one-trait cross, Mendel crossed a tall pea plant with a short pea plant. The first generation, called F1, had all tall plants.

When F1 plants self-pollinated, the second generation, called F2, had tall and short plants.

This showed that the short trait did not disappear. It remained hidden in the F1 generation and appeared again in F2.

Monohybrid cross flow:

TT × tt → all Tt

Tt × Tt → TT, Tt, Tt, tt

A single copy of T is enough to make the plant tall. So, tallness is dominant and shortness is recessive.

Dihybrid Cross and Independent Inheritance of Traits

Mendel also studied two traits at the same time. He crossed pea plants with round yellow seeds and wrinkled green seeds.

The F1 plants had round yellow seeds. In F2, new combinations appeared.

The new combinations showed that traits are inherited independently. Seed shape and seed colour do not always remain linked.

F2 ratio in a two-trait cross:

9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green

This explains independent inheritance of traits.

Dominant and Recessive Traits in Heredity Class 10 Notes

Dominant traits express themselves even when only one copy is present. Recessive traits express themselves only when both copies are recessive.

In the combination Tt, the plant is tall because T is dominant. The short trait t is present but not expressed.

Both TT and Tt plants are tall in phenotype. Only tt plants are short.

Class 10 Science Chapter 8 Notes on Genes and Chromosomes

Each sexually reproducing organism has two copies of each gene. One copy comes from the father and one from the mother.

Germ-cells carry only one set of genes. When two germ-cells combine, the normal chromosome number is restored.

Genes are present on chromosomes. Each chromosome is an independent piece of DNA.

This explains why traits can be inherited independently. Different chromosomes can separate and recombine during germ-cell formation.

Sex Determination in Human Beings in Class 10 Science Chapter 8 Notes

Sex determination explains how the sex of a child is decided. In human beings, sex is largely genetically determined.

Humans have 22 pairs of regular chromosomes and one pair of sex chromosomes.

All children receive one X chromosome from the mother. The father can contribute either X or Y.

The sex of the child depends on whether the sperm carries X or Y chromosome. The father’s chromosome contribution determines the sex of the child.

Important Points of Heredity Class 10 Notes

These quick notes cover the main facts from CBSE Notes Class 10 Science Chapter 8.

Useful Links for Class 10 Science