Chapter 15-How Organisms Evolve - Chapter 15 How Organisms...

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Chapter 15: How Organisms Evolve
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Here is a quick review of some terminology you need to keep in mind Genes- segment of DNA Alleles- code of DNA that makes trait dominant or recessive. Genotype- combination of alleles (i.e. AA) Phenotype- actual physical trait (i.e. brown) Homozygous dominant- 2 dominant (AA) Heterozygous- 1 dom, 1 rec. (Aa) Homozygous recessive- 2 recessive (aa)
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Review of Genetics These bands are genes This gene has a dominant allele This gene has a recessive allele
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What do these terms have to do with Evolution? We can observe in a population the frequency of the dominant and recessive allele. If we can measure that frequency and it changes over time, then organisms will change. Thus EVOLUTION!
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Evolution occurs in populations, NOT individuals You will personally never evolve, but populations of humans will. This is because populations share a gene pool - the sum of all the genes in a population. Variation or differences in alleles or traits makes the gene pool more diverse.
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Evolution is the change of Allele frequencies. Allele frequency – add up all the alleles of a gene for all the individuals in that population. EX: 100 pea plants contain 200 alleles of the gene that control flower color. If 50 of those alleles are for purple color, then 50/200 (or .25) is the frequency of that allele in the population.
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What if 100 alleles code for white flowers, the frequency of the allele 1. .10 2. .15 3. .25 4. .50 5. .75
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5 Causes of Evolution (this is how evolution happens) 1. Mutation 2. Genetic Flow 3. Genetic Drift 4. Non-Random mating 5. Natural and Sexual Selection
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1. Mutations
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Mutations Cause Allele Frequencies to Change in Natural Populations Mutation - a change in the base sequence of the DNA molecule. Mutations can be good or bad.
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Things to remember about DNA DNA is the code to make protein A change in protein may change the appearance or an organism Each newborn will probably only have 1 or 2 mutations that differ from their parents. May seem small, but very important for evolutionary change
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More about Mutations A mutation does not arise as a result of, or in anticipation of, environmental forces.
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