Evolution - It is the change over time in the proportion of individuals in a population differing in one or more inherited traits. During this process there are changes in allele frequency., Natural selection and sexual selection - Non-random processes causing evolution., Genetic drift - Random process causing evolution., Small populations - Genetic drift is more important in these populations, as alleles are more likely to be lost from the gene pool., Population bottlenecks - It occurs when a population size is reduced for at least one generation., Founder effects - It occurs through the isolation of a few members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool , A gene pool - It is altered by genetic drift because certain alleles may be under-represented or over-represented and allele frequencies change., Variation - It arises in traits as a result of mutation, Mutation - It is the original source of new sequences of DNA. New sequences can be novel alleles. Most of them are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual, Natural selection - 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 - It is the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring. This type of selection may lead to sexual dimorphism., Female choice - It involves females assessing the fitness of males, Selection pressures - They are the environmental factors that influence which individuals in a population pass on their alleles. Where they are strong, the rate of evolution can be rapid. , Examples of selection pressures - They can be biotic: competition, predation, disease, parasitism; or abiotic: changes in temperature, light, humidity, pH, salinity., The Hardy-Weinberg (HW) principle - This principle can be used to determine whether a change in allele frequency is occurring in a population over time. Changes suggest evolution is occurring, The conditions for maintaining the HW equilibrium - no natural selection, random mating, no mutation, large population size and no gene flow (through migration, in or out, Fitness - It is an indication of an individual’s ability to be successful at surviving and reproducing., Absolute fitness - It is the ratio between the frequency of individuals of a particular genotype after selection, to those before selection., Relative fitness - It is the ratio of the number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype.,

KA2 a) Drift and selection and b) Fitness

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