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Transcript
Find this presentation online at http://www.redwood.org/stewart 10.02 1 I. What is evolution? Review. A. Change over time. Evolution occurs in a punctuated equilibrium that includes gradual changes (due to natural selection) and rapid changes (due to stochastic factors). 1. Natural Selection: The mechanism for gradual evolution. 1. Variation, 2. Selection, 3. Reproduction 2. Stochastic Factors Random events effect the outcome of evolution (often cause rapid changes). These include droughts, volcanic eruptions, etc. These lead to… genetic drift. Genetic drift is the change in genetic makeup of a population caused by stochastic factors and isolation. It is more noticeable in small populations. 10.02 2 I. What is evolution? Review. B. When a new species evolves, speciation has occurred. On the Galapagos, 1 finch species (the “founding fathers and mothers”) evolved into 13 different species. This speciation was due to isolation (allopatric speciation). New species can also evolve due to selection and competition (sympatric speciation). It is called Adaptive radiation or divergent evolution when many species evolve from one species. 10.02 3 II. Measuring Evolution A. Simulations Data generated by models simulating selection, reproduction and stochastic factors demonstrate evolution. The Effect of Stochastic Factors on the Number of Variations Remaining in the Final Populuation 8.0 7.0 Number of Variations (Colors) 6.0 5.0 4.0 3.0 2.0 1.0 0.0 10.02 Main land Is land Near/L arge Is land Dista nce/Size Is land Far/Small 4 II. Measuring Evolution B. Phenotypic/ physical measurements See the Grant’s work with Galapagos Finches: Generational data shows natural selection and stochastic factors lead to evolution. 10.02 5 II. Measuring Evolution C. Allele frequencies 1. Hardy and Weinberg argued that if five conditions are met, a population's allele (number of A’s [p] and a’s [q]) and genotype frequency will remain constant from generation to generation (and, consequently, no evolutionary change would occur). This balance is known as Hardy-Weinberg equilibrium. Basically, the Hardy-Weinberg equation describes the status quo. If the five conditions are met, then no change (no evolution) will occur in either allele or genotype frequencies in the population. 10.02 6 II. Measuring Evolution C. Allele frequencies 2. The Hardy-Weinberg Mathematical Formula 10.02 • If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then p represents the frequency of the A (dominant) allele • If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then q represents the frequency of the a (recessive) allele • p+q=1 Always. So when p changes, so must q and vice versa. AND, if p or q changes over time, evolution has occurred. 7 II. Measuring Evolution C. Allele frequencies 3. The conditions of Hardy-Weinberg equilibrium are as follows: 1. Large population 2. Random mating 3. No mutation 4. No migration 5. No selection If all conditions are met, NO EVOLUTION occurs. (Since all of this seldom happens, evolution often does occur). 10.02 8 II. Measuring Evolution Population of Organisms C. Allele frequencies 4. Summary Unique Gene Pool Hardy-Weinberg conditions are met: • no mutation • no migration One or more Hardy-Weinberg conditions are NOT met: But wait! • large population size How does all the genetics stuff work? • random mating • no natural selection Allele Frequencies do NOT change Genetic Equilibrium 10.02 Evolution will NOT occur Allele Frequencies change Genetic Disequilibrium Evolution will occur 9 III. Genetics Review A. Raw material for evolution (and, so, a way to measure evolution). -How variation created (mutation) -How selected traits passed on (reproduction) -How change can be measured (allele frequencies) B. How it works 1. Background: vocab gene: codes for a trait allele: form of a gene (A or a) genotype: genetic make-up (AA, Aa, or aa) 10.02 phenotype: trait 10 III. Genetics Review B. How it works 1. Background: vocab dominant: A recessive: a heterozygous: Aa homozygous: AA or aa gamete: reproductive cell (contains half of alleles) meiosis: how gametes form 10.02 11 III. Genetics Review B. How it works 2. Background: meiosis R r u u Z Z 6 genes (12 alleles) P p t t H h 4 chromosomes (2 pairs) MEIOSIS: Sex cells duplicate and divide twice to form daughter cells. Meiosis summary example: how gametes form Only half of alleles present in each cell. These cells can combine with other gametes to form the new cell (zygote) of a new organism. 10.02 R u Z R u Z P t H r u Z P t H r u Z p t h p t h 12 III. Genetics Review Possible alleles from male gamete (sperm) B. How it works 3. Simple: Punnet squares Possible alleles from female gamete (egg) R r r Possible offspring R 10.02 r r r r 13