Asexual vs Sexual Reproduction

• Reproduction is the production of new organisms from existing organisms of the same species.
• Reproduction is essential for species survival and ensures continuity of life.
• Reproduction results in organisms with similar basic characteristics to their parents.

Role of DNA in Reproduction:

• DNA, or deoxyribonucleic acid, is genetic material in chromosomes.
• DNA holds the information needed to make proteins and other molecules that make a cell functional.
• DNA carries information from parent to offspring.
• DNA replication is the process of creating similar copies of DNA during reproduction.
• DNA copies can be similar, but not 100% identical, leading to variations.
• Mutation leads to variation in DNA.
• Variations are useful for a species' survival, allowing organisms to adapt to environmental changes.
• Accumulated variations over time can lead to the formation of new species.

Types of Reproduction

• Asexual reproduction involves one parent.
• Sexual reproduction involves two parents.

Asexual Reproduction

• Asexual reproduction involves the production of new organisms from a single parent without sex cells (gametes).

Sexual Reproduction

• Sexual reproduction involves the production of new organisms from two parents using sex cells or gametes.

Comparison of Asexual and Sexual Reproduction:

• Asexual reproduction involves one parent, while sexual reproduction requires two.
• Asexual reproduction involves cell division by fission, budding, or regeneration, whereas sexual reproduction involves meiosis.
• Asexual reproduction has little chance of variation, while sexual reproduction leads to genetic variation.
• Asexual reproduction does not involve the formation or fusion of gametes. Sexual Reproduction does.
• Asexual reproduction is found in lower organisms. Sexual reproduction is found in higher invertebrates and vertebrates.
• Asexual reproduction can use the whole parent body, a bud, or fragment. Sexual reproduction must use gametes
• Asexual reproduction is completed in a short time, whereas sexual reproduction can take several months.
• Asexual reproduction produces two or more offspring, while sexual reproduction can produce one or more.

Methods of Asexual Reproduction:

• Fission
• Budding
• Spore formation
• Regeneration
• Fragmentation
• Vegetative Propagation

Fission

• Fission is when a unicellular organism splits to form two or more new organisms.
• There are two types of fission: binary fission and multiple fission.
• Amoeba, Paramecium, Leishmania, and Bacteria reproduce by binary fission.
• In binary fission, the parent organism splits to form two new organisms.
• When an amoeba cell reaches its maximum size, its nucleus lengthens and divides into two (karyokinesis), followed by the cytoplasm (cytokinesis), forming two smaller daughter amoebae.
• Fission in Amoeba can occur in any plane, but in Leishmania, it occurs longitudinally with respect to the flagellum.
• Bacteria reproduce through binary fission, where genetic material copies itself, forming two identical copies, then the cell enlarges and divides into two identical daughter cells.
• In multiple fission, the parent organism splits to form many new organisms at the same time like plasmodium.
• During unfavorable conditions, some organisms form a cyst, and the nucleus splits multiple times within the cyst to form daughter nuclei. Cytoplasm collects around each daughter nuclei, and when favorable conditions return, the cyst breaks open, releasing new organisms.

Budding

• Budding occurs when a small part of a parent organism grows out as a bud, detaches, and becomes a new organism.
• Hydra and yeast reproduce by budding.
• A small outgrowth (bud) forms on the sides of the Hydra's body through repeated mitotic division. The bud grows developing a mouth and tentacles, then detaches to live as a separate organism.
• In some organisms, like sponges and corals, the buds remain attached permanently, forming colonies.

Spore Formation

• In spore formation, the parent plant produces microscopic reproductive units called spores within a sporangium (spore case).
• When the spore case bursts, the spores spread into the air and germinate under favorable conditions to produce new plants.
• Fungi like Rhizopus, mucor, bacteria, non-flowering plants, ferns and mosses reproduce by spores.
• The common bread mold plant (Rhizopus) consists of thread-like hyphae and a stem with a sporangium containing hundreds of spores. The spores spread and germinate when these spores land on food or soil.
• Spores are covered by a hard protective coat, enabling them to survive under unfavorable conditions.

Regeneration

• Regeneration is a method of asexual reproduction where an organism forms a complete new individual from its body part.
• Hydra and Planaria show regeneration.
• If a Planaria's body is cut into pieces, each piece can regenerate into a complete Planaria.
• Specialized cells of the cut body part rapidly divide to form a mass of cells that differentiate into various organs and body parts.
• Complex multicellular organisms cannot show regeneration. Specialized cells make up tissue, different tissues make up an organ, different organs carrying out a life process makes up an organ system and finally all the organ systems together make up the entire organism. They have a high degree of organization in their body so they cannot reproduce their whole body through regeneration.

Fragmentation

• Fragmentation is the breaking up of the body of a simple multicellular organism into two or more fragments, each of which grows into a new complete organism.
• Spirogyra, a green filamentous alga, reproduces through fragmentation, where it breaks into fragments, and each fragment grows into a new Spirogyra.

Vegetative Reproduction (Vegetative Propagation)

• Vegetative reproduction (Vegetative propagation) is a process where a part of the plant body gets detached and develops into a new independent plant.
• In lower plants, it occurs through binary fission, budding, fragmentation, gemmule formation, etc.
• In higher plants, modified stems, roots, and leaves are used for natural vegetative propagation.
• There are two types of vegetative propagation: natural and artificial.

Natural Vegetative Reproduction

• Different plant parts are modified for vegetative propagation.
• The common structures (vegetative parts) are roots, stems, leaves, and buds.
• Plants in the process are called vegetative propagules.

Vegetative Propagation by Roots

• Ordinary roots develop adventitious buds, which grow into new plants (e.g., Guava).
• Root tubers with adventitious buds occur in sweet potato, Tapioca, Yam, Dahlia, and Asparagus.
• Buds present on tuberous roots grow into leafy shoots when placed in soil, and the leafy shoots develop adventitious roots to be detached and planted.

Vegetative Propagation by Stems

• This common method uses bulbs, runners, rhizomes, corms, tubers, and offsets.
• Bulbs are modified shoots with a short stem and apical/axillary buds (e.g., onion, garlic, Tulip).
• Runners are creeping stems that produce roots at nodes, breaking into independent plants (e.g., grass, Oxalis).
• Rhizomes are underground, horizontally growing stems with nodes, internodes, and axillary buds (e.g., ginger).
• Corms are condensed rhizomes growing vertically with axillary buds that produce daughter corms (e.g., Saffron, Colocasia)
• Tubers are modified underground stems with "eyes" or buds (e.g., potato).
• Aerial shoots are stem segments that develop into new plants, similar to sugarcane segments used in agriculture (e.g. Opuntia)

Vegetative Propagation by Leaves

• Leaves of some plants possess adventitious buds for vegetative propagation (e.g., walking fern).
• In Bryophyllum, marginal buds sprout while the leaf is attached. Buds develop on leaves when injured or detached (e.g., Begonia).

Vegetative Propagation by Bulbils

• Bulbils are fleshy buds that develop into new plants upon falling on soil (e.g., Agave, Oxalis, Pineapple, Lily).

Artificial Methods of Vegetative Propagation

• Special techniques used when natural methods are ineffective due to plant cells bring more totipotent than animal cells.
• Cutting is a simple method where a stem or root piece (20-30 cm long) is cut and planted in nutrient-rich soil, then a stem cutting soon develops new roots and grows into a new plant.
• Sugarcane stem cuttings are common in plants like Rose, Croton, Sugarcane, Tapioca, China rose, Bougainvillea, Lemon, Coffee and Grape.
• Layering is a common method where a twig (branch) is bent below the soil, called layering, and a small incision is made to cover the bent portion with soil.
• This covered portion develops new roots and then can be separated to form a new plant.
• The plants it is common in are Jasmine, Strawberry, Grapevine and Cherry.

Grafting

• Grafting joins parts of two different plants to form a composite plant.
• It works efficiently in closely related plants with vascular cambium.
• One plant with a strong root system is selected as the stock, and a branch from another plant (scion) chosen for its superior traits is usually selected.
• The stock's shoot is cut 20-30 cm above the ground, and complementary cuts are made in both stock and scion to fit them together tightly.
• For this fitting, the area is tied, and covered with wax to prevent infection.
• Suitable plants include mango, guava, apple, rubber plant, citrus, and pear.
• This combines the properties of two plants and is used for breeding fruits and flowers.

Tissue Culture (Micropropagation)

• Tissue culture (Micropropagation) produces new plants from a small piece of plant tissue in a suitable growth medium, (tobacco, orchids, rubber, oil palm, papaya.)
  • The tissue is placed in a nutrient and hormone-containing culture medium to form callus.
• Callus is transferred to a growth medium to develop roots, then put on another medium containing plant hormone which stimulates the development of shoot. These are now called plantlets.
• Then plantlets are transplanted into soil to form a mature plant and is used for production of ornamental plants.

Advantages of Tissue Culture

• Technique is very fast.
• The new plants are disease free.
• Very little space and time are needed.
• Plants can be grown around the year.

Advantages of Vegetative Propagation:

• The new plant produced by vegetative propagation is exactly like parent plant.
• Fruit trees yield earlier.
• Many plants can be grown from just one parent plant.
• Seedless plants can be produced.

Disadvantages of Vegetative Propagation:

• Diseases can be contracted by the parent.
• Vegetative organs useful for propagation cannot be persevered for long
• The result provides no genetic variation, and therefore the plants find it difficult to adapt and lose their vigour.
• Vegetative multiplication causes damage most of the plants as there is overcrowding and hence severe competition.