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Variation refers to differences, specifically the range of differences for one feature, within a population A. Asexual Reproduction- ‘without sex’,’ one parent divides to form two organisms 1. The offspring are usually clones of the parent and each other. (genetically identical) 2. Occasionally produces variation if there is a genetic mutation 3. A mutation is: any random change in the genetic material of an organism Mutations occur, every so often, while the DNA is being copied. B. Sexual reproduction: when two parents each contribute genetic info to the offspring 1. Always produces variation: No two offspring will be exactly alike. a. New combinations of genes from the parents can occur in the offspring and offspring can show a trait that neither parent shows. (recessive traits) b. Random genetic mutations contribute to variation in sexual reproduction, too, as ‘mistakes’ are made during egg and sperm production, or when a fertilized egg divides. C. Genetic variation is needed for a population to be able to adapt to changes in the environment. Loss of genetic variation can put a species at risk of extinction. II. Mutations A. Each gene in DNA codes for a specific protein in the organism. B. If the DNA code gets changed, it could cause the protein to be made differently. C. Mutations can be: (1) positive, or helpful, increases ability to survive and reproduce, such as the mutation that allows people to be able to digest lactose after age 5 (2) negative, or have a harmful effect, such as sickle cell anemia (3) neutral, or have no effect, such as an extra toe in cats D. The environment determines if a mutation is positive, negative, or neutral. E. Mutations for positive traits are more likely to be passed on to the next generation than mutations for negative traits F. Some mutations might be helpful in the heterozygous (‘carrier’) state, increasing the chances of the mutation continuing in a population ex: sickle cell anemia, protects against malaria in the heterozygous state III. Adaptation: an inherited trait that increases an organism’s chances of surviving in a particular environment long enough to pass on its genes through reproduction; A. positive mutations are passed on and, over generations, lead to adaptations B. Organisms don’t ‘try’ to adjust themselves to meet the needs of the environment; mutations occur randomly (nature decides or selects which are advantageous) C. When an environment changes, some traits may no longer be beneficial and other traits may become beneficial. ex: variation in thickness of fur in rabbits, depends on climate ex: finches and deeper beak depth D. Adaptations can be 1. structural (involving parts/make-up) 2. behavioral 3. physiological (functions) I. Natural selection A. Natural selection is defined as a process by which the best-adapted individuals in a population tend to survive and pass on their traits; survival of the ‘fittest’ (best suited) B. In order for natural selection to occur, conditions must be met: 1. There must be variation in the traits in a population. 2. These traits must be inherited. 3. More individuals are born than can survive (competition for survival). 4. Individuals with beneficial traits leave MORE offspring than other individuals in the same population, causing the genes for beneficial traits to increase in frequency in the population. C. A population usually changes by natural selection over a long period of time; Can happen faster in organisms with (1.) short reproductive cycle (2.) large numbers of offspring such as: rock pocket mice in the desert, blue moon butterfly, bacteria developing antibiotic resistance, Darwin’s finches II. The Theory of Evolution by Natural Selection A. the theory of evolution= the scientific theory that all species are descended from common ancestors who have changed over time by means of natural selection B. A scientific theory is a well-tested scientific explanation; lots of evidence for it C. This theory organizes our understanding of all life on Earth; helps us understand why life is both similar and diverse D. was first proposed by Charles Darwin in 1859 in his book, On the Origin of Species by Means of Natural Selection E. Darwin noticed: 1. species vary globally but similar ecosystems have species with similar traits 2. species vary locally (many related species can be found in an environment) * he collected specimens and made drawings 3. species change over time (he collected fossil and noticed many extinct organisms had traits like those living today.) F. Darwin’s ideas were not well-accepted at the time: 1. religious ideas were influential in people believing that Earth was only a few thousand years old (too little time for natural selection to do its work); Darwin himself was taught that species were ‘fixed’ put there by god. 2. fossil evidence showing connections between organisms was limited 3. Darwin didn’t know how traits were passed from parent to offspring G. As more evidence became available, Darwin’s ideas became more widely accepted. III. Speciation: How do new species come about? A. species = a group of organisms that can interbreed and pass on genes to the following generations B. Speciation is the process of one species developing into two or more species that can no longer mate *can take millions and millions of years C. basic steps of speciation: 1. populations of the same species get separated from one another 2. each population adapts to its own surroundings through natural selection 3. enough changes accumulate so that the populations can no longer mate and produce fertile offspring (changes in mating behavior can be one of these changes) A. selective breeding (also called artificial selection): when humans breed organisms with a desirable set of criteria (rather than the environment determining what is desirable) B. genetic engineering = changing the traits of an organism by directly changing its DNA a. GMO (genetically modified organism)= an organism that was given a new trait by humans directly altering the genetic material 1. for food (can make them more nutritious, easier to grow etc…) 2. for some other purpose, such as making an organism produce a substance needed by humans b. some GMOs are also transgenic, meaning they have genes from an unrelated organism put into their genome C. gene therapy = procedure which inserts a piece of corrective genetic material into a patient’s cells to correct a genetic disorder