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Evolution The Process of Evolution (Variation, Heredity and Differential Reproduction)

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Presentation on theme: "Evolution The Process of Evolution (Variation, Heredity and Differential Reproduction)"— Presentation transcript:

1 Evolution The Process of Evolution (Variation, Heredity and Differential Reproduction)

2 Important things to recall DNA  deoxyribonucleic acid, the macromolecule, composed of two polynucleotide chains in a double helix, that is the carrier of genetic information in all cells Genes  Heredity unit containing specific genetic information. A gene can mutate to various forms called alleles. Alleles  Any of the alternative forms of a given gene Allele Frequency  The relative proportion of all alleles of a gene that are of a designated type. DNA (gene) → RNA → protein → trait

3 Definition of Evolution Any process of change over time. Classically  A change in the relative frequencies of heritable traits within a population across generations. Modern  A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations.

4 Classical Evolution A change in the relative frequencies of heritable traits within a population across generations Relative frequency: 50% Tall plants 50% Short plants 55 generations later 25% Tall plants 75% Short plants

5 Modern Evolution A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations

6 Differential 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 duplication  Genetic drift - stochasticity  Gene Flow – movement of genes from pop. to pop.  Natural selection The 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.

7 Mutation occurs in the trait Mutation directly changes gene frequencies An example of a spontaneous mutation during the development of plant leaves For evolution to occur via this mechanism, what has to be true of the mutation? The mutation has to be heritable The mutation of fruit flies with four wings is an inherited mutation

8 The population size is small Genetic drift – random fluctuations in the allele frequencies Generation 1 p (frequency of R) = 0.7 q (frequency of r) = 0.3 Generation 2 p = 0.5 q = 0.5 Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring Generation 3 p = 1.0 q = 0.0

9 Gene flow Immigration or emigration occurs based on the trait

10 Microevolution Microevolution 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.

11 Mechanisms of Evolution (cont.) Natural Selection  Natural 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 traits The 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

12 Darwin’s Observations Biogeography  It 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 things Agriculture  Selective breeding Fossils  Evidence of organisms no longer present  Evidence that many living organisms were not present in the past Geology  New ideas about the age of the Earth via plate tectonics Economics  Competition for resources and the effects of overpopulation

13 Evolution by Natural Selection (a mechanism of evolution) Population level: If variation exists and If variation is heritableand If differential reproduction (differential selection) exists Then over time, those variations that enhance the ability of the organism to reproduce will increase in any population Natural Selection leads to ADAPTATION

14 Adaptation A 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.

15 Adaptation 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 or  our eyes “adapt” to darkness does not involve genetic change!

16 Adaptation refers to traits that are heritable Acclimation: Changes in the structure or physiology of an individual over its lifetime Examples: Increasing muscle mass via weightlifting High altitude acclimation: But, neither of these involves genetic change!

17 Human 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?

18 Sickle Cell Anemia Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.

19 Sickle Cell Anemia Because 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

20 Flattened tail – aids in swimming Long, sharp claws – Aid in clinging to rocks Salt gland – Allows drinking of salt water Diving adaptations. While diving they:  Reduce blood flow to body surface- helps retain heat  Lower metabolic rate – conserves O 2

21 Imperfect Adaptations Multi-tasking may force an evolutionary compromise Can’t simultaneously optimize distinct functions. traitperformance fitness trait feeding defense thermoregulation

22 Adaptation – organisms are not perfectly adapted ( have to make due with your genetics) Examples: panda thumb

23 All traits evolve from something else, so carry historical baggage thus can be “contrivances” (make do!) Homologous Homologous structures which have a common origin.

24 Divergent Evolution Divergent 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.

25 Convergent Evolution Convergent 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.analogous homologous

26 Wings


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