Heredity Class 10 Notes | Easy Explanation and Diagrams

This chapter is crucial for your CBSE board exams and often appears in both objective and long-answer questions.
In this blog, you'll find simple explanations, key terms, Mendel’s experiments, and must-know diagrams.

Our notes are structured for quick learning and effective revision. Let's dive in

Heredity: The transfer of traits from one generation to the next is termed as heredity. Genes are the functional unit of heredity that transfer characteristics from parents to offspring.

Inheritance: Each new generation inherits both a common basic body design and subtle differences from the previous generation. These changes are passed down during reproduction.

Variations arise usually during the process of sexual reproduction.

In asexual reproduction, offspring are almost identical to the parent. Minor differences arise due to small inaccuracies in DNA copying.

Causes of Variation in sexual reproduction

·         The minor variations arising during sexual reproduction are caused by slight inaccuracies in DNA copying.

·         In sexual reproduction, variations are also caused by crossing over process during meiosis.

·         Combination of genetic material from two parents.

Sexual reproduction produces offspring with similar body design of the parents. However, the offsprings are not identical and show a great deal of variation from the parents.

Importance of Variation:

·         It ensures stability of the population.

·         It helps the species to adapt in the changing environment.

·         It supports evolution.

·         DNA variation leads to different forms of a species and the creation of new species.

Key Words

Monohybrid cross is a cross between two pea plants with one pair of contrasting characters. e.g., Cross between a tall and a dwarf plant (short)

Dihybrid cross is a cross between two plants having two pairs of contrasting characters. e.g., Cross between green round seed with a yellow wrinkled seed.

Phenotype is the characteristic which is visible in an organism whereas genotype is the genetic composition of an individual.

Genotype: The genetic makeup of an organism, representing the combination of alleles.

Chromosomes: Chromosomes are thread-like structures in the cell nucleus that carry genetic information (DNA).

Laws of Inheritance

Gregor Johann Mendel (1833 & 1884) started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms.

Mendel was known as the Father of Genetics.

Plant selected by Mendel was Pisum sativum (garden pea). Mendel used a number of varieties of garden pea to study the inheritance of seven pairs of contrasting characters.

Mendel performed his experiments on pea plants due to following reasons:

·         Easy to grow.

·         Short life-cycle.

·         The flowers of the pea plant are bisexual.

·         Characteristics of traits can be distinguished properly.

v  First he crossed between two pea plants with one pair of contrasting characters means cross pollination between a tall and a dwarf plant (short). (monohybrid cross)

v  The result was that all the offsprings in the F1 generation were tall. (first generation is written as F1)

v  To investigate the disappearance of the short trait, he allowed the first generation plants to self-pollinate.

v  In the F2 generation, he observed both tall and short plants in a ratio of 3:1.

Based on above monohybrid cross, he proposed Law of Dominance.

ü  Law of Dominance: When parents having pure contrasting characters are crossed then only one character expresses itself in F1 generation. This character is the dominant character and the character which cannot express itself is called recessive character.

v  Then he crossed between two plants having two pairs of contrasting character means cross pollination between green round seed with a yellow wrinkled seed.(Dihybrid cross)

v  In the first generation, all offspring had round yellow seeds.

v  To investigate the missing traits of wrinkled and green seeds, he self-pollinated these plants.

v  In the second generation, he found new combinations of traits along with the original ones, revealing that seed shape and color are inherited independently of each other.

Based on above Dihybrid cross, he proposed Law of Segregation and Law of Independent Assortment

ü  Law of Segregation: It states that every individual possesses a pair of alleles for a particular trait. During gamete formation, a gamete receives only one trait from the alleles. A particular trait can be dominant or recessive in a particular generation.

NOTE: Alleles are alternate forms of genes. For e.g., The gene for eye color has several alleles. Two major alleles are: brown and blue.

ü  Law of Independent Assortment : It states that alleles of different characters separates from each other during gamete formation.

The flow chart given in the next page is important. Students are advised to practice it.

Sex Determination

Environmental factors: In certain reptiles, such as turtles and crocodiles, the temperature at which eggs are laid determine the sex of the offspring.

o   Higher temperature results in female, while lower temperatures result in males.

Genetic factors: The sex of the baby is determined by the type of male gamete that fuses with female gamete.

In humans , the genes inherited from our parents decide whether we will be boys or girls.

In humans, there are 23 pairs of chromosomes. 22 pairs are autosomes and one pair is sex chromosome.

In Male sex chromosome is XY.

In Female sex chromosome is XX.

If X carrying sperm fertilises the egg/ovum then the child will be a female.

If Y carrying sperm fertilises the egg/ovum then the child will be a male.

The following diagram in this context is important. Students are advised to practice this. Very often students are asked to draw such flow charts.

Sources I have used to make the notes

Oswaal_CBSE_Class_10_Science_Revision_Notes_For_2023_Exam

NCERT Class 10 Science Book

Heredity and Evolution  - Short Notes (Prashant Kirad)