Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Genetic drift wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Dual inheritance theory wikipedia , lookup
History of genetic engineering wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Designer baby wikipedia , lookup
Group selection wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Population genetics wikipedia , lookup
Peppered moth evolution wikipedia , lookup
Evolution and Natural Selection Review Presentation for Biology Keystone Assessment Created by Joshua Collins 2011 Table of Contents 1) What is Evolution? 2) Natural Selection 3) Evidence for Evolution 4) Evolution in Action 1) What is Evolution? 2) Natural Selection 3) Evidence for Evolution Section 1 of 4: What is Evolution? 4) Evolution in Action 1) What is Evolution? Evolution the process by which species gradually change over many generations through natural selection. Important things to consider: • No individual organism can evolve, but given the right conditions over enough time, traits within a population will gradually change until the entire population is different. • Populations tend to evolve due to external environmental factors such as predators, food sources, and changes in climate. • New species arise through this very process, and all life on earth can be traced back to simpler common ancestors. • Species A group of organisms that evolved together and are genetically similar enough that they can mate and produce fertile offspring. • Adaptation A specific physical trait or instinctual behavior that has evolved within a species to help it survive in its environment. • Micro-evolution Evolution within a species over several generations. • Macro-evolution Long term evolution over thousands of generations or more, leading to the origination of new species (called speciation). Keep in mind, there really is no difference between micro and macro-evolution, except the amount of time. Common ancestor of species A1 and A2. Species A1 Species A Species A2 Two distinct species, no longer capable of interbreeding. If one population becomes separated into two isolated groups, given enough time, the two groups will become different species. • Outer twigs represent species. • Kingdoms and phyla represented by the thicker branches of the tree. • Splitting branches show new species branching off from a shared ancestor. • Closely related species branched off from each other more recently. • Distantly related species branched off much closer to the bottom. • All the species share a common ancestor at the trunk of the tree. Common ancestor (shared by all the descendants) A dead end branch represents an extinction. Where is the most recent common ancestor between squirrels and whales? All these species trace their lineage back to this common ancestor, essentially the first mammal. Less related to a cow More related to a cow cow Sharks and cows have a very ancient common ancestor Pigs and cows have a relatively recent common ancestor. All vertebrates trace back to this common ancestor. 1) What is Evolution? 2) Natural Selection 3) Evidence for Evolution Section 2 of 4: Natural Selection 4) Evolution in Action 2) Natural Selection Charles Darwin Natural Selection • The driving mechanism behind evolution, as explained in Darwin’s Origin of Species • Certain organisms survive to pass on their traits to successive generations, but most do not. • Often summed up as “survival of the fittest” Darwin’s work was heavily influenced by the previous ideas of other naturalists, including Malthus’ research on population. No population can grow indefinitely. Many more offspring are born than will actually survive to pass on their genes. Therefore, individuals must compete for resources to survive. For example: If every baby robin survived to adulthood and reproduced, it would only take a few decades before the entire planet would be overrun by robins! Obviously, this does not happen! Darwin recognized that limited resources in any environment lead to a “struggle for existence”, in which the traits of some individuals will give them an advantage over others. However slight this advantage, it will lead to certain traits being “selected” by nature to survive and reproduce… Hence, natural selection! These pigeons have all been bred by humans to have certain exaggerated characteristics. Darwin also realized that natural selection is basically the same process that humans have used for centuries in selective breeding of domesticated animals as well as plants for agriculture. Selective breeding, or “artificial selection” is the same process that has led to all the variation we see in dog breeds today. • In artificial selection, humans speed up the change in traits by doing the selecting themselves. • In natural selection, nature itself is doing the selecting over thousands of generations. 1) Natural Selection Darwin knew this • The mechanism (driving force) for evolution, as explained by Charles Darwin. • Explains changes in an entire species or population (not individuals) over time. Darwin didn’t 2) Mutations • Random changes in DNA are sometimes passed on to offspring. • Some helpful; some harmful; some neutral • Only traits that increase reproductive fitness will continue to be passed on. know this because he didn’t know about… A T Deoxyribonucleic Acid G C • Ironically, Darwin never found out about the work of Gregor Mendel, who was experimenting with pea plants right around the same time, in order to figure out how traits are inherited. • It was decades later that Mendel was finally recognized as the father of genetics. • For Darwin, this was the one missing piece of the puzzle that would have vindicated his entire theory. • It wouldn’t be until 1953 that the genetic code itself was finally cracked by Watson and Crick in their discovery of the doublehelix structure of DNA. • Gene A section of DNA that codes for a particular protein, physical trait, or function • Allele One of two (or more) different forms of a gene; For example, for the eye color gene, one allele codes for blue eyes, while the other codes for brown. Often, one allele is dominant over the other. • Genotype The combination of alleles for a particular gene; one allele comes from the mother and the other from the father. • Phenotype The trait that results from the genotype Genes are made up of complex combinations of the base pairs. A T GC • Some genes code for proteins and enzymes. • Some genes turn other genes on or off. • Large sections of DNA code for NOTHING! • If stretched out, the DNA from the nucleus of each cell in your body would be over 6 feet long! • Billions of DNA bases have to be copied every time your body makes new cells, which happens continuously. • There are over 50 trillion cells in your body! • A mutation is simply when there is an error in this copying process. • This happens all the time! • When the right kind of mutation happens in the right kind of way, the mutated gene becomes part of the gene pool and natural selection continues. Keep in mind: Mutations themselves are random “mistakes”, but natural selection is not random! The tiniest genetic change will be favored if it increases an organism’s chances for survival or reproduction, even the slightest bit. These tiny changes accumulate over the course of millions of years until the descendants have gradually diverged from their ancestors into a new species (or multiple different species). Natural selection occurs through the following steps: 1) 2) 3) 4) Overproduction Inherited variation Competition Reproduction 1) Overproduction Parents produce more offspring than will survive. Similarly, plants produce thousands of seeds even though only a few may germinate. 3) Competition In any population, organisms must compete for resources to survive. Some individuals have traits which allow them to survive better than others; often referred to as “survival of the fittest”. 2) Inherited Variation There are genetic differences in any population which result in many combinations of different traits among offspring. These traits are passed genetically from parents to offspring. 4) Reproduction Those who have a survival advantage are more likely to reproduce and pass on their favorable genes and traits to successive generations, resulting in new adaptations and eventually new species. The peppered moth study is a perfect case study of natural selection in action. • In the early 1800s, a common moth species in England had light-colored peppered wings, which helped it blend in with the light bark on the trees in the area. • This camouflage trait helped the moth avoid being eaten by birds. • In 1848, a new dark form of the moth began appearing, and by the turn of the century, the dark variety made up the vast majority of the moth population. Why did the light moths die off, while the dark ones flourished? • Something must have changed that gave the dark moths a survival advantage. • Scientists recognized that moths were changing in response to a change in their environment. • Extensive air pollution from industrialization was causing the tree bark to darken with coal soot. 1) Overproduction Peppered moths lay many eggs, and out of those that hatch, the vast majority of them will be eaten and will not survive to lay eggs of their own. 3) Competition Since there are so many moths, some will survive, but most will die. The ones that survive tend to be the ones that have traits favorable for survival, in this case, camouflage. 2) Inherited Variation Traits for light or dark color are passed on genetically, and moth offspring tend to have traits similar to their parents. However, within a population, some are lighter and some are darker. 4) Reproduction The moths that best blend in with their surroundings will be more likely to survive to adulthood and lay eggs, which will yield offspring with those same favorable camouflage traits. Can you spot the moth? Keep in mind: • No individual moth ever changed its color. Some moths simply survived better than others, changing the allele frequency, therefore changing the appearance of the color traits among the entire population. • In other words, the light moths didn’t become darker. They just tended to die out, allowing the dark moths to take over! Can you spot the moth? Keep in mind: • No individual moth ever changed its color. Some moths simply survived better than others, changing the allele frequency, therefore changing the appearance of the color traits among the entire population. • In other words, the light moths didn’t become darker. They just tended to die out, allowing the dark moths to take over! Long after the Industrial Revolution, pollution regulations have helped to clean the soot from England’s trees. And guess what happened to the dark moths… Dark-colored moths started to be eaten more and more as the tree bark lightened, eventually allowing the light moths to repopulate once again.