* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download what is Natural Selection
Survey
Document related concepts
Quantitative trait locus wikipedia , lookup
Dual inheritance theory wikipedia , lookup
No-SCAR (Scarless Cas9 Assisted Recombineering) Genome Editing wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Pathogenomics wikipedia , lookup
Minimal genome wikipedia , lookup
Genome evolution wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Adaptive evolution in the human genome wikipedia , lookup
Group selection wikipedia , lookup
Genetically modified crops wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Population genetics wikipedia , lookup
History of genetic engineering wikipedia , lookup
Transcript
EVOLUTION What is Natural Selection and What conditions make it possible? From On The Origin of Species “Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle for life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection (pp.80-81) Major points Organisms in a population have heritable variations More organisms are born than resources or environment can support Organisms with traits that give a survival advantage will be favored Favored organisms will reproduce more From National Science Education Standards 1. 2. 3. 4. Evolution is the consequence of the interaction of The potential of species to increase in number The genetic variation among offspring due to mutation and recombination of genes A finite supply of the resources and stable environments required for life The ensuing selection of those offspring better able to survive limited resources and changing environments and leave offspring Let’s explore a scenario A farmer sprayed his barn and cattle with a solution of insecticide A. The insecticide killed nearly all the flies. Sometime later, however, the number of flies was again large. For a second time, the farmer sprayed with insecticide A. The result was similar to that of the first spraying. Most, but not all, of the flies were killed. Again, within a short time, the population of flies increased, and they were again sprayed with Insecticide A. This sequence of events was repeated five times; then it became apparent that insecticide A was becoming less and less effective in killing the flies. Pair up and discuss Explain what happened Darwins Evolution Evolution by Natural Selection was first proposed by Charles Darwin in 1859 Publication of The Origin of Species Also proposed by Alfred Wallace who published a paper at the same time Figure 22.1 The historical context of Darwin’s life and ideas Let’s follow a logical argument Observation 1: All species have great potential fertility & their population size would increase exponentially if all individuals born, reproduced successfully Observation 2: Populations tend to remain stable in size except for seasonal fluctuations Observation 3: Environmental resources are limited Therefore Inference 1: Production of more individuals than the environment can support, leads to a struggle for existence among individuals of a population with only a fraction of offspring surviving each generation Observation 4: Individuals of a population vary in their characteristics. No two individuals are alike Therefore Inference 2: Survival in the struggle for existence is not random & depends in part on the heredity of the individuals. Those individuals whose inherited traits best fit them to their environment are likely to leave more offspring than less fit individuals. Inference 3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population with favorable characteristics accumulating over the generations Dark moths on light colored bark are easy targets for hungry birds but are hidden on pollution darkened trees. Consequences of Overproduction of Offspring 1. 2. 3. 4. Food might become scarce Territories might be limiting for both mating and reproducing Density might get so great that disease and parasites would become epidemics Predator populations will also grow because of the increase in population size of prey, and begin to whittle down the herd. Why do organisms vary? Living organisms vary as a result of sexual reproduction Meiosis allows a large variety of genetically different gametes to be produced by each individual (2n) where n = haploid chromosome # 23 = 8,000,000 different gametes E.g. Humans 2 without crossing over. This occurs through segregation of maternal and paternal chromosomes and crossing over in prophase I of meiosis (exchange of pieces of chromosomes). Fertilization allows alleles from 2 different individuals to be brought together in one new individual (1/8,000,000 x 1/8,000,000 Variations Evolution in Response to Environmental Change Antibiotic resistance in Bacteria: In 1950, Japanese physicians began to notice that some patients suffering from bacterial dysentery, which produces severe diarrhea, did not respond to antibiotics which had been effective in treating this type of infection Apparently resistance to the antibiotics had evolved in certain strains of shigella the pathogen Eventually, researchers identified the specific genes that conferred antibiotic resistance Antibiotic resistance II Some of these genes coded for enzymes that destroyed certain antibiotics such as tetracycline and ampicillin. These genes turned out to be carried on plasmid, now called R plasmids for resistance. Exposure of a bacterial population to a specific antibiotic will kill antibiotic sensitive bacteria, but not those that have the R plasmid The theory of Natural Selection predicts that “The fraction of the population carrying the R plasmid will increase” Antibiotic resistance III Resistant strains have increased since that time R plasmids can pass from one bacterial cell to another through conjugation (bacterial sex) Some R plasmids carry as many as 10 genes for resistance to that many antibiotics This can occur because of transposons, or transposable elements or “jumping genes” In bacterial cells transposons can move within chromosomes, from the plasmid to the chromosome or vice versa, and from plasmid to plasmid Antibiotic resistance IV Transposons bring multiple genes for antibiotic resistance into a single R plasmid by moving the genes to that location from other different plasmids. A sort of bacterial recombination for favorable mutations Without invoking transposons, when doctors encounter an antibiotic resistant strain of bacteria they simply switch antibiotics. Resistance to the new antibiotic soon develops so another switch is made. Resistance to this soon develops… This is how multi drug resistant bacterial strains have evolved Other examples of Natural Selection Evolution of Insecticide-resistant Insects Occurred in 100’s of species of insects Insecticides used to kill insect pests in farmlands, swamps, backyards & homes Some examples include DDT, now banned in many countries & malathion Early results were encouraging small amounts dusted on a crop may kill 99% of insects Evolution of Insecticide – Resistant Insects II Subsequent spraying was less and less effective Resistant animals weren’t killed and their offspring inherited the genes for insecticide resistance In each generation the proportion of resistant insects increases. The population has adapted to a change in its environment Figure 22.12 Evolution of insecticide resistance in insect populations Other examples: Evolution of drug resistant HIV strains Metal tolerance in plants – see ecology and evolution review packet Figure 22.13 Evolution of drug resistance in HIV Resources http://evolution.berkeley.edu Survival of the Fittest? From www.whimsical-art.com