Drift and Selection

• Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits
• During evolution, changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift
• Natural selection acts on genetic variation in populations
• Populations produce more offspring than the environment can support
• Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation
• Sexual selection is the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring
• Sexual selection may lead to sexual dimorphism
• Sexual selection can be due to male-male rivalry and female choice
• Genetic drift occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the nex
• Genetic drift is more important in small populations, as alleles are more likely to be lost from the gene pool
• The importance of bottleneck and founder effects on genetic drift
• A gene pool is altered by genetic drift because certain alleles may be under-represented or over-represented and allele frequencies change
• Where selection pressures are strong, the rate of evolution can be rapid
• The Hardy-Weinberg (HW) principle states that, in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations
• The HW principle can be used to determine whether a change in allele frequency is occurring in a population over time
• Changes suggest evolution is occurring