Natural Selection

• Genetic variation is heritable whereas environmental variation is non heritable
• Genetic variation is caused by mutation, crossing over, random assortment in meiosis and random gamete fertilisation
• Genetic variation leads to discontinuous variation as there are no intermediates, it is often controlled by a gene with multiple alleles
• Environmental variation will affect the way genes are expressed, food availability, pH and climate will impact epigenetics leading to differing phenotypes and intermediates
• Environmental variation can be polygenic (controlled by many genes) and follows a normal distribution
• Natural selection is influenced by selection pressures, advantages against these increase survival, predation, disease, competition and climate change all impact natural selection
• Natural selection determines frequencies of alleles in the gene pool
• Overproduction of offspring in species with a high death rate will increase chances of alleles being passed onto offspring and ensures the population is large enough to survive
• In natural selection, a selection pressure will apply to a population, a random mutation in a large interbreeding population will provide an advantage to the organism, increasing chances of survival and reproduction, the favourable alleles will be passed on to offspring, increasing the frequency of that allele in the gene pool
• Disruptive selection is where extreme phenotypes are favoured, both phenotypes provide an advantage in an environment and intermediate alleles are non advantageous, those with the favourable extreme phenotypes are more likely to survive and reproduce, passing on their alleles to offspring over many generations until two distinct populations form
• Disruptive selection is a form of evolution