By Dr Adrian Mascia(Ph.D Biology, Education. M,
2009, teacher of the year
TYPES OF REPRODUCTION
Reproduction: The creation of a new generation of single cells, single celled organisms or multi-cellular organisms. The production of new organisms will always begin with the division of a single cell.
A–sexual:
Reproduction without the assistance of another organism
Sexual:
Requires two organisms of the same species to combine gametes to form a zygote
A-SEXUAL REPRODUCTIONThere are several methods of A-sexual reproduction
1. Fission2. Spore formation3. Budding4. Fragmentation5. Vegetative reproduction
A-sexual reproduction is very rapid, however does not provide genetic diversity, this can put at species at risk of extinction should conditions change
Fission
• Fission involves the replication of chromosomal DNA
• Once replication occurs, the DNA strands are attached at opposing ends of a cell membrane, and cell division occurs (giving rise to 2 identical cells)
• This is a very rapid process (exponential)• E.G Amoeba
Spore Formation• Spores are hardy, self
contained capsules containing DNA
• Spores are generally mass produced, and are very effective as they will only leave their dormant state when conditions become suitable (increasing chance of survial)
• E.G ferns, mosses, some prokaryotes and protists
Budding• Budding involves the
development of a new organism from the out growth of a parent organism.
• The new organism may detach at some point and become a stand alone organism
• E.G Hydra, some flat worms, yeast cells
Fragmentation• Some organisms such as
sponges have the ability to fragment as well as re-construct themselves
• A sponge can be broken into many pieces, forming many new organisms
• Can also reform a new organism from fragments
Vegetative Propagation• There are some species
of plants from which you can regrow a clone of the original plant by planting cuttings
• This process also allows for a process called grafting, where two different plant cuttings (root and shoot) can be combined to produce a new plant
SEXUAL REPRODUCTION
• Basic process of Meiosis (two gamete cells fusing to form a zygote)
• Creates genetic diversity (essential for the survival of a species)
• Not as fast as A-sexual reproduction
Sexual reproduction in Uni Cellular organisms
• Common misunderstanding that single celled organisms reproduce only A-sexually
• If this were the case we would not see the amazing diversity of single celled organisms
• Several protozoan have the ability to produce gametes
• Generally one gamete is larger and sedentary and one is smaller and mobile (much like in humans)
• Paramecium does not involve gamete production, rather an exchange of genetic material whilst lined up along side one another. This process is called CONJUGATION