CH Reproduction in Animal (Notes)
Part 1: Basics of Reproduction
1. Introduction – Meaning and Importance of Reproduction
Reproduction is the biological process by which living organisms produce new individuals of their own kind.
It ensures the continuity of life on Earth and prevents species from becoming extinct.
Every organism passes its genetic information (DNA) to its offspring.
All living organisms reproduce – non-living things never do.
Daily Example: A cat gives birth to kittens which closely resemble the mother.
Olympiad Insight: Reproduction maintains genetic continuity between generations and supports evolution through
variations.
2. Types of Reproduction – Sexual and Asexual
Two main modes occur in animals:
Type Parents Involved Gametes Offspring Nature Examples
Asexual One Not involved Identical to parent (clone) Amoeba, Hydra
Sexual Two Involved (sperm + egg) Genetically different Humans, Frogs, Birds
3. Need for Variation and Genetic Continuity
Variation: Small differences in traits among individuals of the same species.
Genetic Continuity: Passing of genes from one generation to the next.
Variations help organisms adapt and survive under changing conditions.
Reproduction ensures both continuity and controlled variation for evolution.
Olympiad Point: In asexual reproduction → no variation.
In sexual reproduction → variations arise due to gene recombination.
4. DNA, Genes and Heredity
DNA (Deoxyribonucleic Acid) stores and transfers hereditary information.
Genes are specific segments of DNA controlling traits like eye colour, height, etc.
Heredity ensures offspring resemble parents yet have small differences.
During reproduction, DNA replicates and passes from parents to offspring.
Example: Eye colour, blood group, and dimples are inherited through genes.
5. Link Between Life Span and Reproduction
Every organism has a life span – birth → growth → maturity → death.
Reproduction usually occurs before death, ensuring the species continues.
The time and pattern of reproduction vary among species.
o Example: Insects lay hundreds of eggs; elephants reproduce slowly.
The balance between reproduction and death keeps ecosystems stable.
6. Comparison Between Asexual and Sexual Reproduction
Aspect Asexual Sexual
Number of Parents One Two
Gamete Involvement Not involved Involved
Variation Absent Present
Speed Rapid Slower
Energy Use Less More
Examples Hydra, Amoeba Humans, Birds, Frogs
7. Role of Reproduction in Evolution
Reproduction + Variation = Evolution.
Species evolve as advantageous traits are passed down generations.
Reproduction helps species adapt and survive environmental changes.
Organisms unable to reproduce or adapt → extinction.
Example: Giraffes evolved long necks through variations passed across generations.
,1. Asexual Reproduction – Definition and Characteristics
Asexual reproduction involves only one parent.
There is no formation or fusion of gametes (no sperm or egg).
The offspring produced are genetically identical to the parent, known as clones.
This method is common in simple or lower organisms.
It is a fast, energy-efficient mode of reproduction.
No variation is introduced in the offspring.
Daily Example: Amoeba divides into two identical daughter cells through binary fission.
2. Binary Fission (Amoeba, Paramecium)
“Fission” means splitting or division.
In binary fission, the parent organism divides into two equal parts, each forming a new organism.
Common in unicellular organisms like Amoeba and Paramecium.
Process:
1. The nucleus divides first into two parts (nuclear division).
2. Then the cytoplasm divides, forming two daughter cells.
3. Each new cell grows into a complete organism identical to the parent.
Example:
In Amoeba, division occurs in any direction (irregular fission).
In Paramecium, division is across a fixed line (transverse fission).
3. Multiple Fission (Advanced Form)
The parent cell divides into many daughter cells simultaneously.
Occurs when conditions are unfavourable (organism forms a protective cyst).
The nucleus divides repeatedly inside the cyst to form many nuclei.
When conditions improve, the cyst breaks, and each nucleus becomes a new organism.
Example: Plasmodium (malaria parasite).
4. Budding (Hydra, Yeast)
In budding, a small outgrowth or bud develops on the parent’s body.
The bud grows gradually by cell division.
Once mature, it detaches from the parent to live independently.
Sometimes, multiple buds form — creating colonies.
Examples:
Hydra → Buds appear as small bumps, grow, and detach.
Yeast → A small bud forms on the parent cell, enlarges, and separates after maturity.
, 5. Fragmentation and Regeneration (Planaria, Starfish)
Fragmentation:
The parent body breaks into two or more pieces, and each piece develops into a new
organism.
Seen mainly in simple multicellular organisms.
Example: Planaria can regenerate into complete organisms from each fragment.
Regeneration:
Ability of an organism to regrow lost body parts.
Occurs due to specialized regenerative cells.
Common in organisms with simple body structure.
Example:
Starfish → A lost arm can regrow into a full new organism.
Lizard → Can regrow its tail (limited regeneration).
6. Spore Formation (General Overview)
Spores are tiny, single-celled reproductive bodies capable of growing into new
individuals.
They are covered with a tough outer wall, protecting them from heat and dryness.
Common in bacteria, fungi, and some protozoans.
Though rare in animals, similar mechanisms exist in primitive species.
Example: Some protozoans form spores under adverse conditions.
7. Artificial Methods – Cloning and Modern Examples
Cloning:
Cloning is the process of producing identical copies of organisms artificially.
It is a modern scientific form of asexual reproduction.
The clone has exactly the same genetic material as the parent.
Famous Example:
Dolly the Sheep (1996) → First mammal cloned from an adult body cell.
o Scientist: Ian Wilmut (Scotland).
o Dolly was genetically identical to her mother.
Other Modern Applications:
Cloning of plants for agriculture.
Cloning of animals for research or conservation.
8. Difference Between Asexual and Sexual Reproduction
Aspect Asexual Reproduction Sexual Reproduction
Number of Parents One Two
Gametes Not involved Involved
Genetic Variation None – offspring are identical Present – offspring show differences
Speed Fast Slow
Energy Requirement Low High
Part 1: Basics of Reproduction
1. Introduction – Meaning and Importance of Reproduction
Reproduction is the biological process by which living organisms produce new individuals of their own kind.
It ensures the continuity of life on Earth and prevents species from becoming extinct.
Every organism passes its genetic information (DNA) to its offspring.
All living organisms reproduce – non-living things never do.
Daily Example: A cat gives birth to kittens which closely resemble the mother.
Olympiad Insight: Reproduction maintains genetic continuity between generations and supports evolution through
variations.
2. Types of Reproduction – Sexual and Asexual
Two main modes occur in animals:
Type Parents Involved Gametes Offspring Nature Examples
Asexual One Not involved Identical to parent (clone) Amoeba, Hydra
Sexual Two Involved (sperm + egg) Genetically different Humans, Frogs, Birds
3. Need for Variation and Genetic Continuity
Variation: Small differences in traits among individuals of the same species.
Genetic Continuity: Passing of genes from one generation to the next.
Variations help organisms adapt and survive under changing conditions.
Reproduction ensures both continuity and controlled variation for evolution.
Olympiad Point: In asexual reproduction → no variation.
In sexual reproduction → variations arise due to gene recombination.
4. DNA, Genes and Heredity
DNA (Deoxyribonucleic Acid) stores and transfers hereditary information.
Genes are specific segments of DNA controlling traits like eye colour, height, etc.
Heredity ensures offspring resemble parents yet have small differences.
During reproduction, DNA replicates and passes from parents to offspring.
Example: Eye colour, blood group, and dimples are inherited through genes.
5. Link Between Life Span and Reproduction
Every organism has a life span – birth → growth → maturity → death.
Reproduction usually occurs before death, ensuring the species continues.
The time and pattern of reproduction vary among species.
o Example: Insects lay hundreds of eggs; elephants reproduce slowly.
The balance between reproduction and death keeps ecosystems stable.
6. Comparison Between Asexual and Sexual Reproduction
Aspect Asexual Sexual
Number of Parents One Two
Gamete Involvement Not involved Involved
Variation Absent Present
Speed Rapid Slower
Energy Use Less More
Examples Hydra, Amoeba Humans, Birds, Frogs
7. Role of Reproduction in Evolution
Reproduction + Variation = Evolution.
Species evolve as advantageous traits are passed down generations.
Reproduction helps species adapt and survive environmental changes.
Organisms unable to reproduce or adapt → extinction.
Example: Giraffes evolved long necks through variations passed across generations.
,1. Asexual Reproduction – Definition and Characteristics
Asexual reproduction involves only one parent.
There is no formation or fusion of gametes (no sperm or egg).
The offspring produced are genetically identical to the parent, known as clones.
This method is common in simple or lower organisms.
It is a fast, energy-efficient mode of reproduction.
No variation is introduced in the offspring.
Daily Example: Amoeba divides into two identical daughter cells through binary fission.
2. Binary Fission (Amoeba, Paramecium)
“Fission” means splitting or division.
In binary fission, the parent organism divides into two equal parts, each forming a new organism.
Common in unicellular organisms like Amoeba and Paramecium.
Process:
1. The nucleus divides first into two parts (nuclear division).
2. Then the cytoplasm divides, forming two daughter cells.
3. Each new cell grows into a complete organism identical to the parent.
Example:
In Amoeba, division occurs in any direction (irregular fission).
In Paramecium, division is across a fixed line (transverse fission).
3. Multiple Fission (Advanced Form)
The parent cell divides into many daughter cells simultaneously.
Occurs when conditions are unfavourable (organism forms a protective cyst).
The nucleus divides repeatedly inside the cyst to form many nuclei.
When conditions improve, the cyst breaks, and each nucleus becomes a new organism.
Example: Plasmodium (malaria parasite).
4. Budding (Hydra, Yeast)
In budding, a small outgrowth or bud develops on the parent’s body.
The bud grows gradually by cell division.
Once mature, it detaches from the parent to live independently.
Sometimes, multiple buds form — creating colonies.
Examples:
Hydra → Buds appear as small bumps, grow, and detach.
Yeast → A small bud forms on the parent cell, enlarges, and separates after maturity.
, 5. Fragmentation and Regeneration (Planaria, Starfish)
Fragmentation:
The parent body breaks into two or more pieces, and each piece develops into a new
organism.
Seen mainly in simple multicellular organisms.
Example: Planaria can regenerate into complete organisms from each fragment.
Regeneration:
Ability of an organism to regrow lost body parts.
Occurs due to specialized regenerative cells.
Common in organisms with simple body structure.
Example:
Starfish → A lost arm can regrow into a full new organism.
Lizard → Can regrow its tail (limited regeneration).
6. Spore Formation (General Overview)
Spores are tiny, single-celled reproductive bodies capable of growing into new
individuals.
They are covered with a tough outer wall, protecting them from heat and dryness.
Common in bacteria, fungi, and some protozoans.
Though rare in animals, similar mechanisms exist in primitive species.
Example: Some protozoans form spores under adverse conditions.
7. Artificial Methods – Cloning and Modern Examples
Cloning:
Cloning is the process of producing identical copies of organisms artificially.
It is a modern scientific form of asexual reproduction.
The clone has exactly the same genetic material as the parent.
Famous Example:
Dolly the Sheep (1996) → First mammal cloned from an adult body cell.
o Scientist: Ian Wilmut (Scotland).
o Dolly was genetically identical to her mother.
Other Modern Applications:
Cloning of plants for agriculture.
Cloning of animals for research or conservation.
8. Difference Between Asexual and Sexual Reproduction
Aspect Asexual Reproduction Sexual Reproduction
Number of Parents One Two
Gametes Not involved Involved
Genetic Variation None – offspring are identical Present – offspring show differences
Speed Fast Slow
Energy Requirement Low High
