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Gravity just a theory The study of the rules governing the maintenance and transmission of genetic variation in natural populations What are the three components necessary to get evolution by natural selection? Some phenotypes must give advantage to some individual over others and this phenotype must have a genetic component What if Darwin had known about this??!! Mendel’s Laws: Segregation Independent assortment Mendel’s Garden SEXUAL REPRODUCTION CONTRIBUTES TO VARIATION Example – A Line Cross Experiment Consider 2 diploid individuals with 3 loci and 2 alleles Parents: aabbcc F1 progeny: x AABBCC AaBbCc F2 progeny: AABBCC AABbCC AAbbCC AaBBCC AaBbCC AabbCC aaBBCC aaBbCC aabbCC AABBCc AABbCc AAbbCc AaBBCc AaBbCc AabbCc aaBBCc aaBbCc aabbCc AABBcc AABbcc AAbbcc AaBBcc AaBbcc Aabbcc aaBBcc aaBbcc aabbcc 27 COMBINIATIONS Population Genetics What were the definitions of evolution? Population genetics – Tracks the fate of Mendelian genes across generations – Allele or genotype will become more or less common over time? – Start to answer…. Some Definitions: Population: A freely interbreeding group of individuals Gene Pool: The sum total of genetic information present in a population at any given point in time Phenotype: A morphological, physiological, biochemical, or behavioral characteristic of an individual organism Genotype: The genetic constitution of an individual organism Locus: A site on a chromosome, or the gene that occupies the site Gene: A nucleic acid sequence that encodes a product with a distinct function in the organism Allele: A particular form of a gene Genotype Frequency: The relative proportion of a particular genotype in a population Allele Frequency: The relative proportion of a particular allele at a single locus in a population Assumptions: 1) Diploid, autosomal locus with 2 alleles (A and a) 2) Simple life cycle: aAAa aAAaAa a aAAa aAaAA a aAAa a a aAa aAA AaA A little History Hardy’s Proof General Rule for Estimating Allele Frequencies from Genotype Frequencies: Genotypes: AA Frequency: p2 Frequency of the A allele: Frequency of the a allele: Aa aa 2pq q2 Sample Calculation # 1: Allele Frequencies Sample Calculation # 2: Allele Frequencies Main Points: p+q=1 p2 + 2pq +q2 = 1 Two populations with markedly different genotype frequencies can have the same allele frequencies Hardy The Hardy-Weinberg Law A single generation of random mating: – Equilibrium reached Weinberg p2 + 2pq + q2 = 1 H-W ASSUMPTIONS: IMPLICATIONS OF THE H-W PRINCIPLE: 1) A random mating population reaches equilibrium in a single generation 2) External force that changes frequencies leads to a new equilibrium 3) Heterozygosity maximized when allele frequencies intermediate FOUR PRIMARY USES OF THE H-W PRINCIPLE: 1) Track genes 2) Null model 3) Forensic analysis 4) Summarize diversity DETECTING DEPARTURES FROM HWE Step 1: Determine allele frequencies Step 2: Calculate the expected number of each genotype DETECTING DEPARTURES FROM HWE Step 3: Calculate ? test statistic Step 4: Compare this result to critical value 6.25 > 5.99, so this is a significant departure from HWE! EVOLUTIONARY THOUGHT AFTER DARWIN Evolution accepted quickly Natural selection was not! – Why? Wanted there to be meaning to life I’m gonna bolo your ass Bring it! United Mendelian population genetics with the inheritance of continuous traits 1890-1962 1892-1964 Migration Effective population size Population subdivision Adaptive landscapes On his 90th birthday 1889-1988 Outcomes of the “MODERN SYSTHESIS” THE EXTENSION OF H-W TO LOCI WITH MANY ALLELES Does HW principle still apply if we have lots of alleles? EXAMPLE: APPLICATIONS OF H-W TO FORENSICS PROBABILITY OF A FALSE POSITIVE PRODUCT RULE: With multiple loci, the probability of a false positive is simply equal to the product of the locus-specific probabilities As this probability becomes small, we become more confident that the match is real