Evolution_Populations - Populations Without variation...

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Populations Without variation (which arises from mutations of DNA molecules to produce new alleles ) natural selection would have nothing on which to act. A population is a group of individuals living in the same geographical area and sharing a common gene pool. The gene pool is the sum of all genetic information carried by the members of a population. Much genetic variation in a population is generated by mutation. Mutation is any heritable change in DNA. Mutations can be changes of a single nucleotide base or may involve changes in chromosome number. Whether a mutation is good, neutral, or harmful depends on how it affects survival and reproductive success. Population Genetics A population is a group of potentially interbreeding organisms of the same species occupying a certain area. Members of a population vary from one another. This variation is the raw material on which natural selection operates. There are several types of mutations, both at the gene-level and the chromosome-level. Gene mutations provide new alleles, making these mutations the ultimate source of variation. A gene mutation is an alteration in the DNA nucleotide sequence , producing an alternate sequence, termed an allele. Mutations occur at random, and can be beneficial, neutral, or harmful. Some chromosomal mutations are changes in the number of chromosomes inherited, while others are alterations in arrangement of alleles on chromosomes. In sexually reproducing organisms, genetic recombination is
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the reallocation of alleles and chromosomes. Recombination results from crossing-over during meiosis , the random segregation of chromosomes to gametes during meiotic division, and the random combination of gametes during fertilization . The entire genotype is subject to natural selection since new combinations of alleles may have improve the reproductive success of the organism. For polygenic traits, the most favorable combination may occur when the right alleles group by recombination. Not only are variations created, they are also preserved and passed on from one generation to the next. The gene pool is the total of all the alleles in a population, in the context of gene frequencies. Neither dominance nor sexual reproduction will change allele frequencies. The Hardy-Weinberg Law This law states an equilibrium of allele frequencies in a gene pool (using a formula p 2 + 2pq + q 2 ) remains in effect in each succeeding generation of a sexually reproducing population if five conditions are met. No mutation: no allelic changes occur. No gene flow: migration of alleles into or out of the population does not occur. Random mating: individuals pair by chance and not according to their genotypes or phenotypes. No genetic drift: the population is large so changes in
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Evolution_Populations - Populations Without variation...

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