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Chapter 3 The Modern Synthesis

Chapter 3 The Modern Synthesis - Chapter 3 The Modern...

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Chapter 3: The Modern Synthesis Population Genetics - The study of what happens to genes in populations that are undergoing natural selection Genes in Population - Biologists describe the genetic composition of a population by specifying the frequency of alternative genotypes - The genotypic frequency is the fraction of the population that carries that genotype - Genotypic frequencies always add up to 0 - A goal of evolutionary theory is to determine how genotypic frequencies change through time How Random Mating and Sexual Reproduction Change Genotypic Frequencies - The events that occur during sexual reproduction can lead to changes in genotypic frequencies in a population - The first step in determining the effects of sexual reproduction on genotypic frequencies is to calculate the frequency of the allele in the pool of gametes o The frequency of an allele is also known as its gene frequency - Next, we must calculate the frequencies of all the genotypes among the zygotes o Use Mendelian genetics and the multiplication rule to come up with the new frequencies of each genotype o The genotypic frequencies will change but the frequencies of the two alleles themselves have not - When no other forces are operating, genotypic frequencies reach stable proportions in just one generation o These proportions are called the Hardy-Weinberg equilibrium If members in the F 1 generation mate at random, the distribution of phenotypes in the F 2 generation will be exactly the same as the F 1 generation - It is not just sexual reproduction alone that alters phenotypic and genotypic frequencies o Clearly, sexual reproduction and random mating alone cannot lead to evolution over the long run; natural selection causes changes in the frequencies of alleles How Natural Selection Changes Gene Frequencies - If different phenotypes are associated with different phenotypes and those phenotypes differ in their ability to reproduce, then the alleles that lead to the development of the favored phenotype will increase in frequency - Selection cannot produce change unless there is variation in the population - Selection does not operate directly n genes and instead, changes the frequency of different phenotypes - The strength and direction of selection depend on the environment The Modern Synthesis The Genetics of Continuous Variation -
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