topic 4-Natural selection and genetic modification

• 1. charles darwin came up with the theory of evolution by natural selection
• Alfred Russel Wallace was a British naturalist and explorer who contributed to the theory of evolution.
• classification-if all living organisms have descended from a common ancestor, then were all related in some way. We now classify organisms based on their characteristics
• antibiotic resistance-we now understand the importance of finishing the course of drugs to prevent resistant bacteria spreading
• Archaea: Single-celled organisms that are not closely related to bacteria.
• selective breeding is when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population
• the main problem with selective breeding is that it can lead to the extinction of a species
• 1. tissue culture involves growing cells on an artificial growth medium
  2. the plants produced in tissue culture are genetically identical organisms
• 1. First choose the plant you want to clone based on its characteristics
  2. you remove several small pieces of tissue from the parent plant.
  3. you grow the tissue in a growth medium containing nutrients and growth hormones. This is done under aseptic conditions to prevent the growth of microbes
• Animal tissue culture is often used in medical research to grow cells from a patient's body
• 1. A sample of the tissue is extracted from the animal
  2. the cells in the sample are separated from each other using enzymes
  3. then they are placed in a cultural vessel and bathed in a growth medium containing all the nutrients that they need . This allows them to grow and multiply
  4. After several rounds of cell division, the cells can be split up again and placed into separate vessels to encourage further growth
• viruses insert DNA into the organisms they infect
• in agriculture, crops can be genetically modified to be resistant to herbicides. Increasing crop yield
• in medicine, researchers have managed to transfer human genes that produce useful proteins into sheep and cows
• Bacillus thuringiensis produces a toxin that kills many of the insect larvae that are harmful to crops