Understanding:
• Many plant species and some animal species have natural methods of cloning
Many species can reproduce asexually and hence possess natural methods of cloning
- All bacteria, the majority of fungi and many species of protists reproduce asexually to produce genetic clones
- While most plants reproduce sexually, they also possess methods of asexual reproduction (vegetative propagation)
- Certain animal species can also reproduce asexually, via a variety of different mechanisms
Animal Cloning Methods
Binary Fission
- The parent organism divides equally in two, so as to produce two genetically identical daughter organisms
- This method of cloning occurs in Planaria (flatworms) but is also common to bacteria and protists (e.g. euglena, amoeba)
Budding
- Cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent
- This method of cloning occurs in Hydra but is also common to many species of yeast
Fragmentation
- New organisms grow from a separated fragment of the parent organism
- This method of cloning is common to starfish and certain species of annelid worms
Parthenogenesis
- Embryos are formed from unfertilised ova (via the production of a diploid egg cells by the female)
- This method of cloning occurs in certain species of insect, fish, amphibians and reptiles
Examples of Animal Cloning Methods
Plant Cloning Methods
Plants have the capacity for vegetative propagation, whereby small pieces can be induced to grow independently
- This is because adult plants possess meristematic tissue capable of cellular differentiation (totipotent)
Virtually all types of roots and shoots are capable of vegetative propagation
- Garlic and onion bulbs are modified plant leaves – all the bulbs in a group are genetically identical
- Underground stems (e.g. potato tubers) can form new plants which are genetically identical to the parent plant
- Certain plants can form horizontal stems called runners (or stolons) that grow roots and develop into clones
Some plants (mainly algae, mosses and ferns) can reproduce asexually by producing spores
- Spores are also produced by certain types of bacteria and fungi
Vegetative Propagation via Plant Stolons
Human Cloning Methods
Even human beings are capable of creating genetic clones through natural means
- Identical twins (monozygotic) are created when a fertilised egg (zygote) splits into two identical cells, each forming an embryo
- Non-identical twins (dizygotic) are created when an unfertilised egg splits into two cells and each is fertilised by a different sperm
- Identical twins will be clones of one another (genetically identical), while non-identical twins will share 50% of the same DNA
Monozygotic vs Dizygotic Twins