Presentation on theme: "Evolution The Process of Evolution (Variation, Heredity and Differential Reproduction)"— Presentation transcript:
1EvolutionThe Process of Evolution (Variation, Heredity and Differential Reproduction)
2Important things to recall DNAdeoxyribonucleic acid, the macromolecule, composed of two polynucleotide chains in a double helix, that is the carrier of genetic information in all cellsGenesHeredity unit containing specific genetic information. A gene can mutate to various forms called alleles.AllelesAny of the alternative forms of a given geneAllele FrequencyThe relative proportion of all alleles of a gene that are of a designated type.DNA (gene) → RNA → protein → trait
3Definition of Evolution Any process of change over time.ClassicallyA change in the relative frequencies of heritable traits within a population across generations.ModernA change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations.
4Classical EvolutionA change in the relative frequencies of heritable traits within a population across generationsRelative frequency:50% Tall plants50% Short plants55 generations later25% Tall plants75% Short plants
5Modern EvolutionA change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations
6Differential Survival of Traits Differential survival of traits in a population means that some characteristics will become more frequent while others occur less or are lost.There are four known processes that affect the survival of a characteristic; or, more specifically, the frequency of an allele:Mutation – error in duplicationGenetic drift - stochasticityGene Flow – movement of genes from pop. to pop.Natural selectionThe production and redistribution of variation is produced by three of the four agents of evolution: mutation, genetic drift, and gene flow. Natural selection, in turn, acts on the variation produced by these agents.
7Mutation occurs in the trait Mutation directly changes gene frequenciesAn example of a spontaneous mutation during the development of plant leavesFor evolution to occur via this mechanism, what has to be true of the mutation?The mutation has to be heritableThe mutation of fruit flies with four wings is an inherited mutation
8The population size is small Genetic drift – random fluctuations in the allele frequenciesOnly 5 of 10 plantsleaveoffspringOnly 2 of10 plantsleave offspringGeneration 1p (frequency of R) = 0.7q (frequency of r) = 0.3Generation 2p = 0.5q = 0.5Generation 3p = 1.0q = 0.0
9Gene flowImmigration or emigration occurs based on the trait
10MicroevolutionMicroevolution is the occurrence of small-scale changes in gene frequencies in a population over a few generations, also known as change at or below the species level.
11Mechanisms of Evolution (cont.) Natural SelectionNatural selection, the last of the four forces, is based on three principles:(a) there is VARIATION within a species and this variation is HERITABLE(b) parents have more offspring than can survive(c) surviving offspring have favorable traitsThe mechanism by which it operates is termed survival of the fitter meaning differential mortality and fertility.Differential mortality is the SURVIVAL rate of individuals before their REPRODUCTIVE AGE. If they survive, they are then selected further by differential fertility – that is, their total genetic contribution to the next generation.VARIATION HERITABLE SURVIVAL TO REPRODUCE
12Darwin’s Observations BiogeographyIt is the study of distributions of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living thingsAgricultureSelective breedingFossilsEvidence of organisms no longer presentEvidence that many living organisms were not present in the pastGeologyNew ideas about the age of the Earth via plate tectonicsEconomicsCompetition for resources and the effects of overpopulation
13Evolution by Natural Selection (a mechanism of evolution) Population level:If variation exists andIf variation is heritable andIf differential reproduction (differential selection) existsThen over time, those variations that enhance the ability of the organism to reproduce will increase in any populationNatural Selection leads to ADAPTATION
14AdaptationA biological adaptation is an anatomical structure, physiological process or behavioral trait that has evolved over a period of time by the process of natural selection that increases the likely hood of producing larger numbers of offspring or its reproductive success.A heritable characteristic of an organism that helps it to survive and reproduce in a particular environment.
15Adaptation vs. Acclimatization Evolutionary biologists refer to an adaptation as a trait that evolved as the result of natural selection.Physiologists use “adaptation” when they mean “acclimatization” –A nerve “adapts” to a continual stimulus orour eyes “adapt” to darknessdoes not involve genetic change!
16Adaptation refers to traits that are heritable Acclimation: Changes in the structure or physiology of an individual over its lifetimeExamples:Increasing musclemass via weightliftingHigh altitude acclimation:But, neither of these involves genetic change!
17Human example of an adaptation: Sickle Cell Anemia In North America, sickle cell anemia is uncommon and a disadvantage.However, in other parts of the world, specifically areas where malaria is common, the occurrence of sickle cell anemia is greater.Why?
18Sickle Cell AnemiaBecause the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.
19Sickle Cell AnemiaBecause the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.DNA (gene) → RNA → protein → trait
20Flattened tail – aids in swimming Long, sharp claws – Aid in clinging to rocksSalt gland – Allows drinking of salt waterDiving adaptations. While diving they:Reduce blood flow to body surface- helps retain heatLower metabolic rate – conserves O2
21Imperfect Adaptations traitperformancefitnessfitnesstraitfeedingdefensethermoregulationMulti-tasking may force an evolutionary compromiseCan’t simultaneously optimize distinct functions.
22Adaptation – organisms are not perfectly adapted ( have to make due with your genetics) Examples: panda thumb
23All traits evolve from something else, so carry historical baggage thus can be “contrivances” (make do!)Homologous structures which have a common origin.
24Divergent EvolutionDivergent evolution is the process of two or more related species becoming more and more dissimilar.The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees.The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators.
25Convergent EvolutionConvergent evolution is an evolutionary process in which organisms not closely related independently acquire some characteristic or characteristics in common, or the evolution of species from different taxonomic groups toward a similar form.This usually reflects similar responses to similar environmental conditions.Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures which have a common origin.