Unit 11: Evolution (TEST)

• Natural selection: a mechanism by which individuals have inherited beneficial (favorable) adaptations produce fertile offspring

  • Survival of the fittest
• variation: the heritable differences that exist in every population that result from differences in genetic material
• overproduction: species tend to produce more offspring than the environment can support that results in competition between offspring for resources
• adaptation: certain variations within offspring to allow an individual to survive better and live longer
• natural selection acts on phenotypes rather than genetic material itself

  • new alleles are made by genetic mutations
• individuals do not evolve; populations evolve
• natural selection can increase or decrease inheritable traits
• a trait that is favored in one place may be useless or harmful in another place
• Biological resistance: the natural or genetic ability of an organism to avoid or repel attack by biotic agents or abiotic agents
• population: all the individuals of a species that live in the same area
• species: group of organisms so similar to one another that they can breed and produce fertile offspring
• gene pool: total genetic information available in a population
• allele frequency is the number of times that one allele occurs in a gene pool
• allele frequency is determined by dividing the number of a certain allele by the total number of alleles in the population
• knowing allele frequencies allows us to determine if the population is changing (evolving)
• Genetic equilibrium: allele frequencies remain constant, so the population will not evolve
• Wilhelm Weinberg and Godfrey Hardy showed that allele frequencies in a population remain the same from one generation to the next unless acted on by outside forces (genetic equilibrium)
• the hardy-weinberg principle describes a hypothetical population that is not evolving
• hardy-weinberg principle allows scientists to detect changes in the gene pool over time
• hardy-weinberg equation: $p^2+$$2pq+$$q^2=$$1$
• p: dominant allele frequency
• q: recessive allele frequency
• $p^2$:frequency of individuals homozygous for the dominant allele
• $q^2$: frequency of individuals that are homozygous for the recessive trait
• 2pq: the frequency of individual that are heterozygous for alleles
• mutations: change in the nucleotide sequence of an organisms DNA
• Gene flow: movement of alleles in or out of a population as the result of migration of individuals - increases genetic diversity in the new population
• genetic drift: over time a series of chance occurrences can cause a change in allele frequency and loss of diversity (ex: natural disasters)
• nonrandom mating: many species do not mate randomly and choose who they produce with, causing the amplification of certain traits in the population and decreases in genetic diversity
• directional selection: alters the average value for a trait, increasing the allele frequency for the phenotype in one direction or the other
• disruptive selection: conditions favor individuals with both phenotypic extremes at the expense of average individuals
• stabilizing selection: reduces variation in population by acting against both extreme phenotypes and favoring the average form of a trait
• speciation begins with isolation: the gene pools of two populations must become separated for them to become new species
• geographic isolation: physical separation of members of a population
• reproductive isolation: the inability of the members of two populations in the same area to interbreed and produce fertile offspring
• habitat isolation: two species are in the same area, but different habitats rarely encounter each other
• behavioral isolation: two populations are capable of\ interbreeding but have differences in courtship rituals
• temporal isolation: two or more species reproduce at different times
• mechanical isolation: closely related species may attempt to mate but fail because they are anatomically incompatible
• speciation: the evolutionary process by which populations evolve to become distinct species