Exam # 3 Study Guide Lectures: 19 -25 Lecture 19 (March 23) Know the differences between artificial selection, natural selection Natural Selection = gradual non-random process by which traits become more or less common in a species BASED ON DIFFERENTIAL REPRODUCTION Artificial Selection = non-random process by which traits become more or less common in a species because HUMANS ARE SELECTING WHICH ORGANISMS HAVE OFFSPRING What are the preconditions for evolution by natural selection Variation in traits - can be phenotypic (like a bigger nose) - a protein difference (technically phenotypic but not visible) This variation must lead to differences among individuals in LIFETIME REPRODUCTIVE SUCCESS Variation among individuals must be genetically transmissible to the next generation Is evolution the same as natural selection Nope. Evolution means that through time, species accumulate differences and as a result descendants differ from their ancestors — new species arise from existing ones. - evolution doesn’t say anything about where the changes in the species came from (could be natural selection, genetic drift, random mutations) - natural selection is one way that evolution can happen (so essentially natural selection is a type of evolution?) What are some common misconceptions about evolution •There is no intentionality in natural selection — organism doesn’t develop a trait in order to adapt to an environmental challenge Bio 152 1st EditionEdited with the trial version of Foxit Advanced PDF EditorTo remove this notice, visit:www.foxitsoftware.com/shopping•Change is random, selection doesn’t move in a certain direction •Fittest isn’t the fastest or the healthiest, it is reproductive success •All adaptations are not perfect fits for the environment but animals work with the tools they have. Be able to determine from data like the bean experiment why selection is not working A selection of pinto beans were purchased from two different markets. The size and number of the beans were tabulated as shown at right. A selected group of large beans were planted to grow a second generation. These seeds were then scored for size. If you wished to get bigger beans in the next generation. Which population would you select from? (note that A and B are different strains of pinto beans) -would select from population D (right bottom) because you’ve already selected from A and B (which gave you C and D) -when compared to its parental population the mean of D has gotten bigger while when you compare C to its parental population the mean has stayed the same So what happened from group A-C? -you selected the larger beans from group A, but if the beans in group C don’t appear any larger it means that the trait was non-heritable. What happened in group B? - Artificial selection — the trait was being selected for in that population and it was heritable which is why D was larger than C. Lecture 20 (March 25) What is necessary for evolution by artificial selection? All of the following preconditions for evolution by natural selection hold true for evolution by artificial selection except what?I. Variation in traits must exists in a populationII. This variation must lead to differences among individuals in lifetime reproductive success III. Variation among individuals must be genetically transmissible to the next generation •they all hold true: one thing is different is that you don’t allow all of them to breed, so all three are true for the organisms you do allow to breed •example = in the video on foxes they only allowed the extremely aggressive ones to breed with each other •it does lead to a difference in reproductive success because those that are allowed to breed have more reproductive success than those in the middle (ones not allowed to breed) Is artificial selection still evolution? YES Lecture 21 (March 27) Be able to determine allele frequencies for genotype frequencies A population of butterflies has the following genotypic frequencies: 45% AA, 35% Aa, 20% aa. Assuming a population of 100 how many total copies of the gene are there (aka how many alleles)? •each of the 100 organisms has one chromosome from mom and one from dad. Each organism has 2 alleles = 200 total copies of the gene in the population A population of butterflies has the following genotype frequencies: 50% AA, 30 % Aa, 20% aa. What is the frequency of the “a” allele? •20% —> 0.2 aa •0.2 + 1/2(0.3) = 0.2 + 0.15 = 0.35 **use the heterozygous condition** A scientist has studied the amount of polymorphism in the alleles controlling the enzyme Lactate Dehydrogenase (LDH) in a species of minnow. From one population, 1000 individuals were sampled. The scientist found the following frequencies of genotypes: AA = .08, Aa = .28; aa = .64. From these data calculate the allele frequency of the "A" allele in this population. •0.08 + 1/2(0.28) = 0.22Studying allele frequencies is not easy as phenotypic traits often aren’t coded for by a single gene. Often you use molecular techniques to examine the sequence of specific genes to look for genetic diversity or to investigate whether selection is ongoing, but let us take one further example of a simple trait. If you have the same butterfly gene and in a new population you know that the allele frequency of “a” is 25% and there are 10% heterozygotes, how many homozygous AA are there in a population of 100 butterflies? •if the allele frequency of a is 25%, 100-25 = 75, so the allele frequency of AA is 75% •using the equation from previous butterfly problems: •0.75 = x + 1/2(.10) **because there are 10% heterozygotes** •x = 0.75 - .05 = 0.70 Gene pool: total alleles available in a population Allele: different versions of a gene Allele frequency: if you take the whole population what is the frequency of a given allele? Genotype frequency: how common a particular gene is in the population Sources of Genetic Variation (all make alleles) 1. Mutation — must be germ line mutation, somatic mutations make no difference (not passed on to offspring) 2. Recombination during meiosis 3. A single gene could get changed, or the promoter region (causing the gene to be expressed more or less often) 4. Migration — someone might move from one population to another, creating more genetic diversity 5. Outcrossing with other species (like neanderthals cross-breeding with european humans thousands of years ago) Why