Heredity notes class 10 explain how traits or characteristics are passed from parents to their offspring through genes, which is why children resemble their parents but are not exactly the same.
Class 10 Heredity Notes, as per the CBSE Class 10 Science syllabus, also focus on variation, which refers to the differences among individuals of the same species.
These variations play a crucial role in adaptation, survival, and the evolution of organisms over generations, helping species adjust to changing environments and ensuring continuity of life.
What is Heredity?
Heredity is the process by which characteristics are passed from parents to their offspring.
This fundamental biological phenomenon explains similarities and differences within a species.
Understanding what is heredity is vital for comprehending evolution and genetics. These class 10 heredity notes help students grasp these basic concepts for their exams.
Heredity Class 10 Notes
This section offers concise explanations of essential concepts related to heredity.
Heredity and Variation
Heredity involves the transmission of features from one generation to the next. Variation refers to the observable differences in characters among individuals of a species.
Variations are crucial for survival, evolution, and the development of new species in changing environments.
Importance of Variations
Survival:
Variations increase the chances of survival of a species in changing environments. For example, heat-resistant bacteria can survive high temperatures.
Evolution:
Variations form the basis of evolution. Over many generations, useful variations accumulate and lead to the formation of new species.
New Characters:
Variations result in the development of new traits, which may provide advantages in adaptation and survival.
Types of Traits
Traits can be categorized based on their origin and transmission.
| Inherited Traits |
Acquired Traits |
| Passed from parents to the next generation. |
Developed during an individual's lifetime. |
| Transmitted through genetic material (DNA). |
Not passed to the next generation. |
| Example: Eye color, attached or free earlobe. |
Example: Learning to dance, muscular body, piercing. |
Key Terms in Genetics
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Gene: A basic unit of heredity, a segment of DNA carrying information for a specific trait.
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Allele: Different forms of a gene. For example, 'T' for tall and 't' for dwarf are alleles of the gene for stem length.
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Chromosome: Thread-like structures in the nucleus, made of DNA, carrying genes.
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Diploid: Cells with two sets of chromosomes (2n), one from each parent.
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Haploid: Cells with one set of chromosomes (n), found in gametes.
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Homozygous: Having two identical alleles for a single trait (e.g., TT or tt).
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Heterozygous: Having two different alleles for a single trait (e.g., Tt).
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Dominant Trait: The trait expressed even when only one copy of the allele is present.
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Recessive Trait: The trait expressed only when two copies of the allele are present.
Mendel's Contributions
Gregor Mendel performed experiments on garden pea plants (Pisum sativum). He chose them for their short life cycle, easy cross-pollination, and distinct contrasting characters. His work laid the foundation for modern genetics.
Contrasting Characters Used by Mendel
| Character |
Dominant Trait |
Recessive Trait |
| Seed Shape |
Round |
Wrinkled |
| Seed Color |
Yellow |
Green |
| Flower Color |
Violet |
White |
| Pod Shape |
Full |
Constricted |
| Pod Color |
Green |
Yellow |
| Flower Position |
Axial |
Terminal |
| Stem Length |
Tall |
Dwarf |
Monohybrid Cross
A monohybrid cross studies the inheritance of one pair of contrasting traits at a time. For instance, crossing a pure tall pea plant (TT) with a pure dwarf pea plant (tt).
The F1 generation shows all tall plants (Tt). Self-pollinating F1 plants yields the F2 generation.
Dihybrid Cross
A dihybrid cross involves studying the inheritance of two pairs of contrasting traits simultaneously. An example is crossing a round, yellow-seeded plant (RRYY) with a wrinkled, green-seeded plant (rryy).
Key Rules of Heredity
Mendel's experiments led to fundamental laws governing inheritance.
Laws of Dominance
The Law of Dominance states that when two contrasting alleles for a particular trait are present together in an organism, only one allele expresses itself, while the other remains hidden. The allele that expresses itself is called the dominant allele, and the one whose effect is masked is called the recessive allele.
In a heterozygous condition (e.g., Tt), the dominant allele (T for tallness) determines the visible trait (phenotype), so the organism appears tall even though it carries one recessive allele (t for shortness). The recessive trait is expressed only when both alleles are recessive (e.g., tt).
Laws of Segregation (Purity of Gametes)
During gamete formation, the two alleles for a heritable character separate from each other. Each gamete receives only one allele from the pair. This ensures that offspring get one allele from each parent.
Laws of Independent Assortment
Alleles for different traits assort independently of one another during gamete formation. This means the inheritance of one trait does not affect the inheritance of another. This law is observed in dihybrid crosses.
Sex Determination in Humans
Sex in humans is determined genetically by chromosomes inherited from parents. Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
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During reproduction, females produce eggs with an X chromosome.
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Males produce two types of sperm: those with an X chromosome and those with a Y chromosome.
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If a sperm carrying an X chromosome fertilizes an egg, the resulting zygote will be XX (female).
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If a sperm carrying a Y chromosome fertilizes an egg, the resulting zygote will be XY (male).
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Therefore, the father's sperm determines the sex of the child.
Heredity Class 10 Notes PDF
Heredity Class 10 Notes PDF provides a clear and structured explanation of how traits are passed from parents to offspring.
These notes cover key topics such as genes, alleles, Mendel’s experiments, dominant and recessive traits, and inheritance patterns in humans.
Designed for easy understanding and quick revision, they help students grasp important concepts, solve numericals confidently, and prepare effectively for CBSE Class 10 exams.
Heredity Class 10 Notes PDF
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