variation

• variation

  variation in a species can be due to differences in:

  • the genes they have inherited
  • the conditions in which they have developed (environment)
  • a combination of genes and the environment
• variation

  • there is usually extensive genetic variation within a population of a species
  • all variants arise from mutations Ana most have no effect on the phenotype, some influence phenotype and very few determine phenotype.
• mutations occur continuously. very rarely a mutation will lead to a new phenotype. if the new phenotype is suited to an environmental change it can lead to relatively rapid changes in the species
• evolution

  • a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
  • the theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago
  • evolution occurs through natural selection of variants that give rise to phenotypes best suited to their environment
• 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
• selective breeding

  • selective breeding is the process by which humans breed plants and animals for particular genetic characteristics. humans have been doing this for thousands of years since they first bred food from crops from wild plants and domesticated animals
• selective breeding

  • involves choosing parents with the desired characteristics from a mixed population. they are bred together. from the offspring, those with the desired characteristics are bred together. thus continues over many generations until all of the offspring show the desired characteristic.
• which characteristics may be chosen?

  • disease resistance in food crops
  • animals which produce more meat or milk
  • domestic dogs with a gentle nature
  • large or unusual flowers
  • however, selective breeding can lead to inbreeding where some breeds are particularly prone to disease or inherited defects.
• genetic engineering

  • a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
  • plant crops have often been engineered to give bigger fruits and be resistant to diseases
  • bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes
• genetic engineering pros

  • treating diseases
  • more efficient food production
• genetic engineering cons

  • unplanned problems caused when changing genetics
  • effects could be passed on
• pros of GM crops

  • increased yield
  • developing nations citizens may lack nutrients in their diets so crops can be engineered to contain vital nutrients
  • GM crops are already being grown in some places with no issues
• cons of GM crops

  • affect the number of wild flowers and insects, reducing biodiversity
  • we do not fully understand the effect of genetically modified crops on human health
  • transplanted genes may get out into the natural environment
• what are GM crops?

  • genes from the chromosomes of humans and other organisms can be cut out and transferred to cells of other organisms
  • crops that have had their genes modified include ones that are resistant to insect attack or herbicides. GM crops generally have increased yields
• modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders
• process of genetic engineering?

  • enzymes are used to isolate the required gene, this gene is inserted into a vector, usually a bacterial plasmid or a virus
  • the vector is used to insert the gene into the required cells
  • teens are transferred to the cells of animals, plants or microorganisms at an early stage of development so that they develop with the desired characteristics.
• what is tissue culture cloning?

  • using small groups of cells from a part of a plant to grow identical new plants. this is important for preserving rare species of plant or commercially in nurseries
• how are cuttings used for cloning?

  • an older but simpler way used by gardeners to produce many identical new plants from a parent plant
• how are embryo transplants used for cloning?

  • splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into the host mothers
• what is adult cell cloning?

  • nucleus is removed from unfertilised egg cell
  • nucleus from an adult body cell such as a skin cell is inserted into the eggs
  • an electric shock stimulates the egg cell to divide to form an embryo
  • the embryo cells contain the same genetic information as the adult skin cell
  • when embryo has developed into a ball of cells, it Is inserted into the womb of an adult woman to develop