B14) VARIATION AND EVOLUTION
Evolution
Selective breeding |
Choosing parents with the desired characteristics from a mixed population |
Chosen parents are bred together. |
From the offspring those with desired characteristics are bred together. |
Repeat over several generations until all the offspring show the desired characteristics. |
A change in the inherited characteristics of a population over time through the process of natural selection.
The theory of evolution by natural selection. | Species of all living things have evolved from simple life forms that first developed 3 billion years ago. | Through natural selection of variants (genotypes) that give rise to phenotypes best suited to their environment or environmental change e.g. stronger, faster. This allows for variants to pass on their genotype to the next generation. | |
If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species. | |
Darwin’s finches
Selective breeding
The process by which humans breed plants/animals for particular genetic characteristics
Humans have been doing this for thousands of years since they first bred food from crops and domesticated animals.
Choosing characteristics | |
Desired characteristics are chosen for usefulness or appearance | |
Disease resistance in food crops. | |
Animals which produce more meat or milk. | |
Domestic dogs with a gentle nature. | |
Large or unusual flowers. | |
Selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects e.g. British Bulldogs have breathing difficulties.
Genetic engineering
Genetically modified crops (GMO) | Crops that have genes from other organisms | To become more resistant to insect attack or herbicides. |
To increase the yield of the crop. |
Genes from the chromosomes of humans or other organisms can be ‘cut out’ and transferred to the cells of other organisms.
Concern: effect of GMO on wild populations of flowers and insects.
Concern: effect of GMO on human health not fully explored
Modern medical is exploring the possibility of GM to over come inherited disorders e.g. cystic fibrosis
Genetic engineering process (HT only) |
1. Enzymes are used to isolate the required gene. |
2. Gene is inserted into a vector – bacterial plasmid or virus. |
3. Vector inserts genes into the required cells. |
4. Genes are transferred to plants/animals/microbes at an early stage of development so they develop the required characteristics. |
Cloning (Biology only)
Cloning techniques in plants/animals | |
Tissue culture | Small groups of cells to grow new plants. Important for preservation of rare plants and commercially in nurseries. |
Cuttings | Part of a plant is cut off and grown into full plant. |
Embryo transplants | Splitting apart cells from animals embryo before they become specialised. New clone embryos are inserted into womb of adult female. |
Adult cell cloning |
1. Nucleus is removed from an unfertilised egg. |
2. Nucleus from body cell is inserted into egg cell. |
3. An electric shock stimulates the egg to divide into an embryo |
4. Embryo cells are genetically identical to adult cells. |
5. When embryo has developed into ball of cells it is inserted into host womb. |
Concern: some people have ethical objections to adult cell cloning e.g. welfare of the animals.
Over time this results in the formation of new species.
Evolutionary trees are a method used by scientists to show how organisms are related
Classification of living organisms
Use current classification data for living organisms and fossil data for extinct organisms