Evolution is a change in the frequencies of different alleles in a species or population over the course of many generations Human Chromosomes gene DNA nucleus Transcription messenger RNA Translation protein cytoplasm A summary of eukaryotic transcription and translation gene DNA etc complementary DNA strand template DNA strand etc codons mRNA etc anticodons tRNA etc amino acids protein etc How Do Mutations in DNA Affect the Function of Genes Mutations Result from Nucleotide Substitutions Insertions or Deletions Mutations May Have a Variety of Effects on Protein Structure and Function Mutations in DNA Point Mutations in DNA may result in the following changes in Protein Silent mutation No change in protein Missense Amino acid substitution Nonsense Stop codon introduced in the middle Frameshift mutations in proteins are due to insertion or deletions in the DNA There are several types of mutations Point Mutations Change 1 nucleotide for another Example THE DOG ATE THE RAT AND CAT THE DOG ATE THE BAT AND CAT Categories and consequences of point mutations Base pair substitution The molecular basis of sickle cell disease a point mutation Glutamic Acid hydrophilic Valine hydrophobic Categories and consequences of point mutations Base pair insertion or deletion Frameshift Mutations Insertion Example A THE DOG ATE THE BAT AND RAT THE DOG AAT ETH EBA TAN DRA T Deletion Example THE DOG ATE THE BAT AND RAT THD OGA TET HEB ATA NDR AT It might be a little counter intuitive but 3 frameshift changes can actually cause the sequence to revert back to normal THE DOG ATE THE RAT AND CAT 1 THE DDO GAT ETH ERA TAN DCA T 2 THE DDO XGA TET HER ATA NDC AT 3 THE DDO XGN ATE THE RAT AND CAT There are several types of selection 1 Natural Selection The unequal survival and reproduction of organisms due to environmental forces resulting in the preservation of favorable adaptations Usually natural selection refers specifically to differential survival and reproduction on the basis of genetic differences among individuals Note Environmental forces can and does include other biological organisms not just climate temperature or geology The differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources 2 Artificial Selection A selective breeding procedure in which only those individuals with particular traits are chosen as breeders used mainly to enhance desirable traits in domestic plants and animals Note Artificial selection results in domestication Researchers have identified corn genes that were preferentially selected by Native Americans during the course of the plant s domestication from its grassy relative teosinte pronounced tA O sin tE to the single stalked large eared plant we know today The study revealed that of the 59 000 total genes in the corn genome approximately 1 200 were preferentially targeted for selection during its domestication 3 Kin Selection a type of natural selection that favors a certain allele because it increases the survival or reproductive success of relatives that bear the same allele Social Insect Colonies Alarm Calls Helpers at the nest 4 Sexual Selection A form of natural selection that depends not on the struggle for existence in relation to other organic beings or to external conditions but on a struggle between the individuals of one sex generally the males for the possession of the other sex Darwin 1871 Note Is sometimes abbreviated Male competition female choice Evolutionary change in a population can occur in a variety of ways Mutations Are the Source of Genetic Variability Evolution by natural selection is another way that allele frequencies can change over generations This can be seen by looking directly at the proportions of alleles in a population The Gene Pool is the sum of the genes in a population The Frequency of Alleles in a Population can be defined by the Hardy Weinberg Equilibrium Equation 1 or 100 p2 2 pq q2 1 or 100 AA Aa aa If these frequencies change from 1 generation to another EVOLUTION HAS OCCURRED The Hardy Weinberg Equilibrium Population Is a Hypothetical Population That Does Not Evolve p2 2pq q2 1 p q 1 In order for the allele frequencies to stay the same the following conditions must be met No mutations No gene flow between populations No movement of alleles into or out of a population The population must be very large All matings must be random No preferences No natural selection All genotypes must reproduce with equal success This can NEVER happen So 2 causes of evolutionary change in a population are 1 MUTATION 2 SELECTION NATURAL OR OTHERWISE Additional causes for gene frequencies to change would be 3 GENE FLOW 4 GENETIC DRIFT What Causes Evolution Gene Flow among populations can also change allele frequencies Gene Flow Allele Frequencies Can Change in Small Populations Just Due to Chance Occurrences This is called GENETIC DRIFT a Population Bottleneck b Founder effect resulting population original population event causing bottleneck time Most species have about 20 40 heterozygous loci Bottleneck effect From an original peccary population with its own gene pool a few individuals squeeze though a bottleneck In this case a few peccaries with the genotype bb survive a catastrophe These individuals become the founders originators of a new peccary population As they reproduce the new gene pool is very different from that of the original population Seals were hunted into near extinction by the late 1890 s one male yielded 25 gallons of oil 20 individuals remained Cheetahs only have about 0 01 heterozygosity meaning that they are essentially clones of each other Genetic drift Founder effect Isolated Founding Populations May Produce Bottlenecks Amish populations in this country were founded by fewer than 200 individuals around 1730 Samuel King and his wife settled in 1744 and carried the recessive trait They passed this on to their children and today the Old Order Amish have a higher than normal instance of Ellisvan Creveld 1 or 2 carriers out of 200 than the rest of the North American population 1 1 000 Mutation on short arm of chromosome 4 Mating Within a Population Is Almost Never Random Sexual Selection is a huge factor in evolution because reproductive success is the way that evolution proceeds Male Competition Female Choice Summary Causes of Evolution Process Consequence Mutation Creates new alleles increases variability Gene Flow Increases similarity of different