BIOLOGY 1202 Descent with Modification a Darwinian View of Life What is evolution and adaptation o Evolution two main ideas 1 Change over time of the genetic composition of a population 2 Decent of modern organisms with modification from preexisting organisms Accumulation of inherited characteristics that enhance organisms ability to survive in specific environments The principle that events in the past occurred suddenly by mechanisms not operating today Geologic change results from mechanisms that operated in the past in the same manner as at the present time The hypothesis that evolution proceeds chiefly by the accumulation of gradual changes o Evolutionary adaptation Pre Darwinian Theory of Evolution o Catastrophism o Uniformitarianism o Gradualism o Lamarck Use and disuse Bodies of living organisms are modified through the use or disuse of parts Inheritance of acquired characteristics These modifications are inherited by offspring o These ideas turned out to be wrong Evolution by Natural Selection o Darwin and Wallace developed the theory independently Darwin voyage of the Beagle Wallace naturalist in Indonesia Natural Selection o The unequal survival and reproduction of organisms due to environmental forces resulting in the preservation of favorable adaptations o Process selects from what is available in the gene pool o New characteristics are not created on demand Unfavorable traits decrease in frequency favorable traits increase Mechanisms Behind Natural Selection o Observations Individuals in a population vary in their heritable characteristics Organisms produce more offspring than the environment can support o Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals Over time favorable traits accumulate in the population Natural Selection A Summary o Natural selection is a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than other individuals because of those traits o Over time natural selection can increase the match between organisms and their environment o If an environment changes or if individuals move to a new environment natural selection may result in adaptation to these new conditions sometimes giving rise to new species o Although natural selection occurs through interactions between individual organisms and their environment individuals do not evolve It is the population that evolves over time o Natural selection can amplify or diminish only those heritable traits that differ among the individuals in a population Thus even if a trait is heritable if all the individuals in a population are genetically identical for that trait evolution by natural selection cannot occur o Environmental factors vary from place to place and over time A trait that is favorable in one place or time may be useless or even detrimental in other places or times Natural selection is always operating but which traits are favored depends on the context in which a species lives and mates Artificial Selection o Selective breeding of organisms to encourage the occurrence of desirable traits o Analogous to natural selection Evolution is supported by an overwhelming amount of scientific evidence Homologous and Analogous Structures o Homologous o Analogous Structures or other attributes in different species that resemble each other because of common ancestry Not similar in function similar in structure Example mammalian forelimbs Structures that are similar in function but not in structure and developmental and evolutionary origin Homologous Structures Vertebrate Embryos o All vertebrates share similar developmental genes o Differences arise by some genes being switched on or off at varying times during development Homologous Structures Biochemistry and Molecular Biology o DNA is universal genetic material o All life forms use approximately the same 20 amino acids to make proteins o All use ATP as the primary form of cellular energy o All use RNA and ribosomes to make proteins Trees vs Scala Naturae o Scala Naturae Ladder of nature see pg 453 o Evolution not about climbing ladder of nature from lower to higher o Evolution is a bush with lineages branching from one another Convergent Evolution o Similarity between 2 organisms structures or molecules due to independent evolution along similar lines rather than descent from a common ancestor Fossil Record o Show change in organisms through time o Change in types of organisms Past organisms differ from present day organisms Many species have become extinct o Not only provides evidence of small scale changes but of origin of major groups E g the cetaceans The Evolution of Populations o The smallest unit of evolution One common misconception about evolution is that individual organisms evolve during their lifetime Evolutionary processes e g natural selection act on individuals but populations evolve Genetic variation makes evolution possible Mutation o Mutations changes in nucleotide sequence of DNA Source of new alleles and genes o Point mutation change in one nucleotide base in a gene o Chromosomal mutations delete disrupt or rearrange many loci on a chromosome o Gene duplications duplication of whole segments of a chromosome o Mutation rate averages 1 in every 100 000 genes per generation Sexual Recombination o In sexually reproducing organisms sexual recombination produces most of the variability in each generation Crossing over during prophase I Independent assortment during metaphase I Variation within a population o Discrete characters classified on an either or basis o Quantitative characters vary along a continuum within a population E g flower color in pea plants E g height weight The Hardy Weinberg equation can be used to test whether a population is evolving Populations o A group of individuals of the same species living in a certain defined area Hardy Weinberg Equilibrium o Describes a population that is not evolving i e allele frequencies don t change o Five assumptions behind H W equilibrium 1 No mutations 2 Large population size 3 No gene flow 4 No natural selection 5 Random mating No migration among populations Equal chance of mating with any other in population Allele Genotype Frequencies o Allele frequencies p frequency of allele 1 q frequency of allele 2 p q 1 o Genotype frequencies p2 frequency of homozygous dominant q2 frequency of homozygous recessive 2pq frequency of heterozygotes p2 2pq q2 1 H W equation
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