bio - natural selection + genetic modification (4)

• There are ethical issues associated with selective breeding, as many people consider it unethical to selectively breed for characteristics wanted by humans if it means that the offspring will suffer, or have a reduced quality of life as a result.
• Darwin came up with the theory of evolution by natural selection, observed variation within members of the same species and that those with characteristics most suited to the environment were more likely to survive.
• Darwin noted that these characteristics could be passed on and wrote 'On the Origin of Species'.
• Wallace was a scientist that worked at the same time as Darwin and came up with the idea of natural selection, independently of Darwin.
• Wallace's observations provided evidence with warning colours of butterflies to deter predators.
• The theory of evolution by natural selection impacts modern biology through classification, antibiotic resistance, and conservation.
• Darwin's theory of evolution by natural selection explains that genetic variation within a population due to differences in their alleles, with new alleles arising due to mutations.
• Things like predation, competition for resources and disease act as selection pressures, affecting an organism's chance of surviving and reproducing.
• Individuals with characteristics that make them better adapted to the selection pressures in their environment have a better chance of survival and so are more likely to breed successfully.
• The alleles that are responsible for the useful characteristics are more likely to be passed on than the less well adapted that may be less likely to survive and reproduce.
• The beneficial characteristics become more common in the population over time.
• Bacteria are labelled resistant when they are not killed by antibiotics which previously were used as cures against them.
• The problem with selective breeding is that it can lead to inbreeding, as breeding those with similar desirable characteristics means it is likely you are breeding closely related individuals, reducing the gene pool as the number of different alleles reduce.
• Late Stone Age tools, used by Homo neanderthalensis and modern Homo sapiens, included pointed arrowheads, spears and hooks, enabling more advanced tasks such as catching fish.
• Stone tools found as part of archaeological digs can be used as evidence for human evolution.
• Early Stone Age tools, used by Homo habilis, were basic pebble tools created by smashing rocks together, used for tasks such as cracking nuts.
• The Five Kingdoms system and the Three Domains system are two ways of classifying organisms based on genetic relationships.
• Stone tools have become more complex as our brains evolved in complexity.
• A pentadactyl limb is a limb with five digits, seen in several organisms, implying that they all come from a common ancestor and each branched off at different stages of evolution.
• Selective breeding is when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristic, a practice that has been happening for many years since animals were domesticated and plants were grown for food.
• Radiometric carbon dating and stratifying rock layers are two main methods used to date these tools.
• In selective breeding, parents with desired characteristics are chosen, they are bred together, from the offspring those with desired characteristics are bred together, and the process is repeated many times until all the offspring have the desired characteristic.
• Once the tissue has developed enough, it can be transferred to compost for further growth.
• Plant cells have been engineered for disease resistance or to have larger fruits.
• Clones have a low survival rate, and tend to have some genetic problems.
• Tissue culture can also be used to culture animal and human tissues outside of the body.
• Tissue culture is a method of culturing living tissue, making it grow outside the organism, within a growth medium.
• In plants, tissue culture involves removing a piece of tissue from a fast-growing region of the plant, such as the root or shoot tip, using aseptic technique, and placing it on a special growth medium containing hormones and nutrients.
• Benefits of tissue culture include producing lots of offspring with a specific desirable feature, increasing the number of crops resistant to bad weather, and can help extremely endangered species, or even bring back species that have become extinct.
• Bacterial cells have been engineered to produce substances useful to humans, such as human insulin to treat diabetes.
• Species with the same genetic make-up have a reduced chance of survival if the environment changes or a new disease arises, as a few organisms with a survival advantage are less likely to die.
• Risks of tissue culture include reducing the gene pool through producing clones, meaning, it is less likely that the population will survive if a disease arises with low diversity in the population.
• Plants can be cloned using tissue culture, producing an entire field of identical crops from a small cutting.
• Genetic engineering involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
• Bacteria develop random mutations in their DNA, creating new alleles which change the bacteria's characteristics.
• This could include the ability to resist certain antibiotics and this is a big advantage.
• In a host who's being treated to get rid of the infection, a resistant bacterium is better able to survive and so lives longer and reproduces more.
• This leads to the allele for antibiotic resistance being passed on to lots of offspring and this becomes more common in the population over time until the population all have antibiotic resistance.
• Fossil evidence shows how developments in organisms arose slowly, using carbon dating and related techniques to estimate when a fossil was formed, giving us a more complete picture of how an organism or species developed over time.
• Examples of these include Ardi from 4.4 million years ago, with feet structure suggesting she climbed trees, long arms and short legs, and a skull volume similar to a chimpanzee.