Evolution

• Evolution is the change over time in the proportion of individuals differing in one or more inherited traits.
• Selection pressures are environmental conditions that can influence which individuals in a population can pass on their alleles. When there are strong selection pressures, the rate of evolution can be rapid.
• Biotic selection pressures include competition, predation and disease.
• Abiotic selection pressures include changes in temperature, light and pH.
• Natural selection is a non-random evolutionary process which acts on the genetic variation within populations. It increases the frequency of alleles that improve the survival chance of an organism, and decreases the frequency of deleterious alleles.
• Variation within populations is a result of mutation. These are the original source of new DNA sequences. Most mutations are harmful or neutral, but can also be beneficial to an individual.
• Populations always produce more offspring than the environment can support. Variation exists within the species due to different mutations. Organisms struggle for survival, and are influenced by selection pressures. Those organisms best suited to the environment survive. Those less well suited die off.
• Sexual selection is a form of natural selection where the increase in allele frequency is determined through the selection of mating partners.
• Sexual selection can lead to extreme physical or behavioural adaptations to attract mates. These adaptations can cause seuxal dimorphism.
• Genetic drift is a random evolutionary process, which causes a random change in the frequency of alleles or genotype in a population.
• Genetic drift is more important in small populations, as alleles are more likely to be lost from the gene pool.
• A population bottleneck is an event that drastically reduces the size of a population for at least one generation. It could be caused by an environmental disaster, overhunting or habitat destruction. Population bottlenecks reduce the gene pool as many allele types are lost, and will leave a population with a much reduced genetic diversity.
• The Founder effect occurs through the isolation of a few members of a larger population. The gene pool of the new population is not representative of that in the original gene pool.
• The Hardy-Weinberg states that in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over generations.
• The five conditions for maintaining the Hardy-Weinberg are: no natural selection, no mutation, no migration, random mating and a large population.
• To determine allele frequency, the equation p+q = 1 is used. P is the frequency of the dominant allele, q is the frequency of the recessive allele.
• To determine genotype frequency, the equation: p2 + 2pq + q2 = 1. P2 is the frequency of the heterozygous dominant genotype, 2pq is the frequency of the heterozygous genotype, and q2 is the frequency of the homozygous recessive genotype.
• Fitness is a measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species.
• Absolute frequency is: frequency of a particular genotype after selection/frequency of a particular genotype before selection.
• If the absolute fitness is 1, then the frequency of that genotype is stable. A value greater than 1 conveys an increase in the genotype, and a value less than 1 conveys a decrease.
• Relative fitness is: number of surviving offspring per individual of a particular genotype/number of surviving offspring per individual of the most successful genotype.
• Co-evolution is the process by which two or more species evolve in response to selection pressures imposed by each other. A change in the traits of one species act as a selection pressure on the other species.
• Symbiosis is co-evolved intimate relationships between members of two different species.
• In a mutualistic relationship, both organisms in the interaction are interdependent on each other for resources or other services. Both organisms gain from the relationship.
• In a commensalism relationship, only one organism benefits, but the interaction does not negatively affect the other organism.
• In a parasitic relationship, the parasite benefits in terms of energy or nutrients, and the host is harmed as the result of the loss of these resources.
• The Red Queen Hypothesis states that: in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species.