Please enable JavaScript.
Coggle requires JavaScript to display documents.
B14 - Variation and Evolution Revision resource - Coggle Diagram
B14 - Variation and Evolution
Revision resource
Variation
Variation is the differences in the characteristics of individuals in a population.
Variation may be due to differences in the genes, the conditions in which organisms develop, or a combination of both genes and the environment.
Evolution by natural selection
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed over 3 billion years ago.
Mutations occur continuously. Very rarely a mutation leads to a new phenotype. If the new phenotypes is suited to an environmental change it can lead to a relatively rapid change in the species.
It two populations of a species become so different they can no longer interbreed to form fertile offspring, they have formed two new species.
Selective breeding
Selective breeding is a process where humans breed plants and animals for desired characteristics.
Desired characteristics include: disease resistance, increased food production in animals and plant, domestic dogs with a gentle nature, and heavily scented flowers.
Problems can occur with selective breeding including defects in some animals due to lack of variation.
Genetic engineering
Genes can be transferred to the cells of animals and plants at an early stage of their development so they develop desired characteristics. This is genetic engineering.
In genetic engineering, genes from the chromosomes of humans and other organisms can be 'cut out' using enzymes. They are then transferred to the cells of bacteria and other organisms using a vector which is usually a bacterial plasmid or virus.
Crops that have had their genes modified are known as genetically modified (GM) crops. These often have improved resistance to insect attack or herbicides and generally produce a higher yield.
Cloning
A modern technique for cloning plants is tissue culture using small groups of cells taken from part of a plant to grow identical new plants. It is important for preserving rare plant species in nurseries as well as for commercial use.
Taking cuttings is an older and simpler method of producing many identical new plants from a parent plant. It is widely used by gardeners.
Transplanting embryos involves splitting apart cells from a developing animal embryo before they become specialised and then transplanting the identical embryos into host mothers.
Adult cell cloning
In adult cell cloning, the nucleus is removed from an unfertilised egg cell. The nucleus from an adult body cell, such as a skin cell, is inserted into the empty egg cell. A small electric shock stimulates the egg cell to divide to form an embryo. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
The cells of the embryo contain the same genetic information as the adult skin cells.
Ethics of genetic technologies
Modern medical research is exploring the possibility of genetic modification to overcome some of inherited disorders.
There are benefits and risks associated with genetic engineering.
Some people have ethical objections to genetic engineering.