Selective breeding and genetic engineering · GCSE Biology

Selective breeding

Selective breeding (artificial selection) is when humans breed plants and animals for particular genetic characteristics. People have done this for thousands of years.
Choose parents with the desired characteristic and breed them together. Then choose the offspring with the desired characteristic and breed them. Repeat over many generations until all the offspring show the characteristic.
Examples: disease resistance in crops, animals that produce more meat or milk, gentle domestic dogs, and large or unusual flowers.
Problem: it can lead to inbreeding, so some breeds are prone to disease or inherited defects, and there is less variation.

Genetic engineering modifies the genome of an organism by introducing a gene from another organism to give a desired characteristic.
Bacteria have been engineered to make human insulin to treat diabetes.
Genetically modified (GM) crops can be resistant to insect attack or to herbicides, or produce bigger, better fruit. GM crops generally give bigger yields.
Concerns: effects on populations of wild flowers and insects, and some people feel the effects of eating GM crops on health have not been fully explored.
Scientists are researching gene therapy to overcome some inherited disorders.

Enzymes are used to cut out (isolate) the required gene.
The gene is inserted into a vector, usually a bacterial plasmid or a virus.
The vector inserts the gene into the required cells.
Genes are transferred to animals, plants or microorganisms at an early stage of development, so they develop with the desired characteristic.

Tissue culture: small groups of cells are grown into identical new plants. It is used to preserve rare plant species and in commercial nurseries.
Cuttings: gardeners take pieces of a plant and grow them into new identical plants.
Embryo transplants: cells from an early animal embryo are split apart before they specialise, and the identical embryos are transplanted into host mothers.
Adult cell cloning: the nucleus is removed from an unfertilised egg cell and replaced with the nucleus from an adult body cell, such as a skin cell. An electric shock makes the egg divide to form an embryo, which is put into the womb of a female. Dolly the sheep was cloned this way.

Selective breeding: Breeding plants or animals with desired characteristics over many generations.
Genetic engineering: Changing the genome of an organism by adding a gene from another organism.
GM crop: A crop plant that has had genes from another organism added.
Inbreeding: Breeding closely related organisms, which reduces variation and can increase inherited defects.
Vector: Something, such as a plasmid or virus, used to carry a gene into a cell.
Plasmid: A small ring of DNA in bacteria, often used as a vector.
Tissue culture: Growing new plants from small groups of cells.
Embryo transplant: Splitting an early embryo and transplanting the identical cells into host mothers.
Adult cell cloning: Putting the nucleus of an adult body cell into an empty egg cell to make a clone.