Overview
This lecture covers the two main types of reproduction—sexual and asexual—highlighting their processes, advantages, and disadvantages, as well as special cases like hermaphroditism.
Types of Reproduction
- Reproduction allows organisms to produce offspring, continuing their species.
- Two main types: sexual (involving two parents) and asexual (involving one parent).
- Hermaphroditism occurs when one parent has both male and female reproductive organs.
Sexual Reproduction
- Involves fusion of male (sperm) and female (egg/ovum) gametes to form a zygote.
- Gametes are haploid; zygote formed is diploid.
- Occurs in most animals, humans, and flowering plants.
- Follows three stages: Pre-fertilization (gamete formation and transfer), Fertilization (fusion of gametes), and Post-fertilization (zygote develops into embryo).
- Fertilization can be external (outside the body) or internal (inside the body).
- Animals are classified by how embryos develop: oviparous (eggs hatch outside), ovoviviparous (eggs hatch immediately after laying), and viviparous (embryo develops inside the mother).
Sexual Reproduction in Plants and Non-Flowering Species
- In flowering plants (angiosperms), the ovary becomes fruit and ovules become seeds after fertilization.
- Spirogyra reproduces sexually by conjugation, forming zygotes that survive adverse conditions.
Advantages and Disadvantages of Sexual Reproduction
- Advantages: genetic variation, hybrid production, chromosome number maintenance, recombination of genetic material.
- Disadvantages: requires two parents, offspring may need care, slower population growth.
Hermaphroditism and Reproduction in Earthworm
- Hermaphrodites (e.g., earthworm, hydra) have both ovaries and testes and can produce both sperm and eggs.
- Earthworms reproduce mainly by cross-fertilization during copulation, resulting in fertilized ova in cocoons.
Asexual Reproduction
- A single parent produces genetically identical offspring (clones) without gamete formation.
- Occurs in both unicellular and multicellular organisms, including plants and animals.
Features and Modes of Asexual Reproduction
- No gamete formation or fertilization; rapid process and limited variation.
- Plant methods: fragmentation, budding, spore formation, and vegetative propagation (natural and artificial).
- Animal methods: fission (binary, multiple), budding, fragmentation, and regeneration.
Asexual Reproduction in Unicellular Organisms
- Binary fission: organism splits into two (e.g., amoeba, paramecium).
- Multiple fission: splits into many (e.g., sporozoans, algae).
Asexual Reproduction in Animals
- Budding creates new individuals from outgrowths (e.g., hydra).
- Fragmentation and regeneration produce new organisms from parts (e.g., planaria, lizard tail).
Pros and Cons of Asexual Reproduction
- Advantages: rapid growth, early maturity, no need for pollinators or dispersal agents, easy local colonization.
- Disadvantages: lack of genetic variation, poor adaptation risks, limited evolution, risk of overcrowding.
Key Terms & Definitions
- Gamete — sex cell (sperm or egg/ovum) with half the chromosome number.
- Zygote — fertilized cell formed from the union of gametes.
- Oviparous — animals that lay eggs; embryos hatch outside the body.
- Ovoviviparous — fertilized eggs develop inside the body and hatch immediately after laying.
- Viviparous — embryos develop inside mother's body, nourished by placenta.
- Hermaphrodite — organism with both male and female reproductive organs.
- Binary fission — parent cell divides into two identical cells.
- Spore formation — reproduction via mitotically produced spores.
- Vegetative propagation — plant reproduction without seeds, using parts like stems or leaves.
Action Items / Next Steps
- Review modes of reproduction in plants and animals.
- Learn examples for each mode (e.g., oviparous, budding, fragmentation).
- Understand differences between sexual and asexual reproduction for exams.