Variation
A genetic variation is the difference in DNA sequences of individuals within the same species. Random fertilization increases genetic variation between offspring due to meiosis and fusing of a random sperm and egg. There are different kinds of variation:
- Genetic - phenotypes depending on inherited alleles from parents, such as eye color or blood type.
- Environmental - adaptation due to environmental conditions such as lifestyle, diet, or climate. For example, white moths have adapted to be darker in more polluted areas. It is important to remember that genetic and environmental variation can interact, like with height. A child may have the genetics to grow tall but if they are malnourished then they will not grow as much.
Mutations
Mutations create variation due to a change in the sequence of DNA in a gene. These changes can be inherited but happen randomly and are rare. Mutations have the potential to:
- Have no effect on the phenotype
- Have a small effect on the phenotype
- If the mutation does have a significant effect, this could either be harmful or beneficial. Beneficial mutations can lead to phenotypes that make individuals better adapted to survive. This is because altering DNA can alter the sequence of amino acids for making proteins, and these proteins are what make the phenotypes. Mutations can occur more frequently due to exposure to ionizing radiation (e.g. gamma rays or X-rays) or exposure to chemical mutagens (e.g. chemicals in tobacco). These mutations can lead to uncontrollable growth, causing a tumor, which means that they are carcinogens (cancer causing).
Evolution and Natural Selection
Evolution is a gradual change in the range of organisms on Earth. New species continually arise from species that already exist, and other species become extinct. This change happens from a change in inherited characteristics of a population due to one mutation in an individual that has then reproduced to give their offspring this characteristic. Darwin proposed this theory after studying animals in the Galapagos Islands in South America in the 19th Century. His 3 key observations were:
- All organisms produce more offspring than those who survive to adulthood
- Established populations of organisms remain roughly the same size
- Members of the same species show variation in characteristics. His 2 main conclusions were:
- All organisms are involved in a struggle for survival
- Some individuals are better adapted to their environments than others, therefore these individuals are more likely to survive and reproduce, passing on their advantageous genes to their offspring.
Examples of Natural Selection and Genetic Variation
An example of natural selection in action is the peppered moth population, where light moths adapted to darker bark on trees in polluted areas were more likely to survive and reproduce, gradually increasing the proportion of dark moths over time. Another example is the evolution of giraffes, with short-necked ancestors evolving into long-necked descendants over many generations due to the need to reach higher levels for food and survival.
Antibiotic Resistance
Bacteria can evolve quickly because they reproduce at a very fast rate. A mutation in a bacteria's DNA could make them resistant to certain antibiotics (such as penicillin) and so will no longer be killed by the antibiotic. A random mutation happens in a single bacteria, this mutation may protect the bacteria against the antibiotic, and these bacteria survive and divide to produce more bacteria containing the antibiotic-resistant gene. This rapid evolution due to mutations can have serious implications for public health and the effectiveness of antibiotics.
In conclusion, natural selection and genetic variation are essential components of evolution and play a significant role in the survival and adaptation of species in their environments. Understanding these concepts is crucial in various fields such as biology, medicine, and environmental science.
