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Micro Evolution -Evolution on the smallest scale -Evolutionary change within a population Read p. 468.

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Presentation on theme: "Micro Evolution -Evolution on the smallest scale -Evolutionary change within a population Read p. 468."— Presentation transcript:

1 Micro Evolution -Evolution on the smallest scale -Evolutionary change within a population Read p. 468

2 Chapter 23 Objectives 1.Mutation and Sexual Reproduction produce genetic variation and allow evolution to occur. 2.To understand the Hardy-Weinberg equation. 3.Natural Selection, Genetic Drift and Gene Flow can alter allele frequencies within a population 4.Natural Selection is the only mechanism that consistently causes adaptive Evolution Only inherited traits are passed on. The color in these caterpillars are due to diet not genetics.

3 Genetic Variation -Genetic variation within a population 1. Gene Variability 2. Nucleotide Variability -Geographic Variation 1. Populations in different locations can have genetic variation 2. Some due to Natural Selection and others by chance. Cline variation due to natural selection Example of chromosomal changes that spread by drift or chance events. (No phenotypic differences between two populations.)

4 Mutations The ultimate source of new alleles 1.Only mutations on gamete forming cells are passed on. (Not Somatic cell mutations) 2.Most mutations arent passed on 3.Point Mutations are changes in at least one base pair. Why are most mutations harmless or neutral? 1.Many mutations happen on the non protein coding part of DNA. 2.If mutation does occur on protein coding portion it may not change the amino acid it codes for. 3.Even if the amino acid changes it may not change the shape of the protein. Mutations that do alter protein coding genes. 1.Deletion, disruption, or rearrangement of protein coding genes results in harmful mutations 2.Duplication can be beneficial. (Olfactory genes in mammals) p. 471 Sexual Reproduction promotes genetic variation by 1.Crossing over 2.Independent Assortment 3.Random Fertilization

5 Populations and Gene Pools -Population is a group of individuals of the same species that live in the same area and interbreed. -Gene Pool is the sum of all alleles within the population -Allele Frequency is the total amount of dominant and recessive alleles in an environment

6 Hardy-Weinberg Principle – Describes a hypothetical population that isnt evolving -A population whose gene pool will remain constant or at equilibrium if only Mendalian segregation and recombination of alleles is at play -Gene pool calculation is the sum of all dominant alleles and the sum of all recessive alleles Hardy-Weinberg Conditions *Populations shift or evolve if at least one of the below conditions arent met (p. 474) 1.No mutations occur 2.Random Mating 3.No Natural Selection 4.Extremely large population size 5.No Gene Flow *Application example p Hardy-Weinberg equation is used to predict percentage of a genotype being heterozygous or homozygous p2 + 2pq + q2 = 1 p = one allele q = different allele

7 Genetic Drift is a condition that alters allele frequencies within a population. P Random events can cause genetic drift ** Small populations 2. The Founder Effect 3. The bottle neck effect Important to note is that a change in allele frequency means the population is evolving. Possible Outcomes -Genetic Drift can lead to loss of genetic variation -Genetic Drift can cause harmful alleles to become fixed in a population

8 Gene Flow also contributes to changes in Allele Frequency -Transfer of alleles into our out of a population -Copper mine example p. 478 Important to note is that a change in allele frequency means the population is evolving.

9 Natural Selection contributes to changing allele frequencies within a population Important to note is that a change in allele frequency means the population is evolving. Individuals phenotypic traits Gives Individual Relative Fitness for Environment Relative Fitness leads to an individuals advantage or disadvantage to reproduce Reproductive success = passing on genes and contributing to the populations gene pool Genotypes indirectly contribute to individuals relative fitness 1. Directional Selection Favors extremes phenotypes mostly caused by extreme environmental changes 2. Disruptive Selection favors phenotypes at both extremes 3. Stabilizing Selection favors intermediate phenotypes **Natural Selection is the only condition that leads to adaptive evolution

10 Limitations to Natural Selection p. 484 Frequency Dependent Selection p. 484 Sexual Selection p Selection can only act on existing variations 2.Evolution is limited by historical constraints 3.Adaptations are often compromises 4.Chance, Natural Selection and the Environment interact


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