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Unformatted text preview: Chapter 25 02:19 Four factors effect allele frequency directly. Inbreeding- selfing ( organisms mate with themselves) Sexual selection- traits helping individuals to attract mates. Sexual selection usually effect more strongly Females invest more in their offspring and are choosy in when it comes to males, for males it the other way around. To study how the four factors effect, in 1908 they invented a mathematical model. There calculation allowed to predict genotype of next generation. Started with the simplest situation, two alleles. Hardy-Weinberg principle Null hypothesis- the principle is a useful null hypothesis to see if one of the commandments has been broken or not. Hardy and Weinberg analyzed what happens to the frequencies of alleles when many individuals in populations mate and produce offspring. They wanted to know what happened in an entire population, when all og the individuals- and thus all possible genotypes-bred. They invented a novel approach: they imagined that all of the gametes produced in each generation go into a single group called the gene pool and then combine at random to form offspring. To determine which genotypes would be present in the next generation and in what frequency, Hardy and Weinberg simply had to calculate what happened when two gametes were plucked at random out of the gene pool, many times, and each of these gamete pairs was then combined to form offspring. These calculations would predict the genotypes og the offspring that would be produced, as well as the frequency of each genotype. Hardy Weinberg P + q= 1, if A1 is 0.7 and A2 is 0.3, then 70% of the gametes in the gene pool carry A1 and 30% carry A2. The possible genotypes are A1A1, A1A2, A2A2. The frequency of the A1A1 is p2. The frequency of the A1A2 is 2pq. The frequency of the A2A2 is q2. P2 + 2pq + q2= 1 Result of this is the Hardy Weinberg, it makes two fundamental claims: 1. if the frequencies of alleles A1 and A2 in a population are givn by p and q, then the frequencies of genotypes A1A1, A1A2, A2A2 will be given by p2, 2pq, q2 for generation after generation. 2. When alleles are transmitted according to the rules of Mendelian inheritance, their frequencies do not change over time. For evolution to occur, some other factor or factors must come into play. The model assumes that mating is random, 5 conditions must be met....
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- Spring '11