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Name________________________ EVOLUTION AND NATURAL SELECTION NOTES Evolution- _____________ in the heritable (genetic) traits of a population over time Note: When we talk about evolution, we are talking about _____________________ changing, not individuals Natural selection- The main _________________ by which evolution occurs Four conditions required for natural selection: 1. Variation- Individuals in a population are not _______________ to each other. 2. Inheritance- Traits are passed to _________________; traits have a genetic basis 3. Environmental population limits- Environmental ________________ ____________ prevent all individuals from surviving to reproduce; some die young. 4. Environmental selection Individuals in the population with more _____________ (advantageous) traits are the ones that survive to reproduce. Individuals without advantageous traits ______ before reproducing. How does natural selection cause evolution of a population? 1. Variation- Members of a population are similar but not identical to one another: Variation in Height Within a Population Example graph: 2. Inheritance- DNA determines the ____________ of individuals Individuals inherit __________ from their _______________ This causes the traits of the offspring to resemble the traits of the ______________ WITH limiting factors (reality) Population Population 3. Environmental population limitsNO limiting factors (not natural) Time Time Examples of limiting factors: 4. Environmental selection Individuals without advantageous traits ______ before reproducing. Individuals with advantageous traits survive to reproduce. Frequency • • Characteristic Populations change, not individuals• The “average” characteristic or other measure of the _____________ changes over ___________________ The environment is the ___________ ______________ behind evolution • • • The ________________ determines which characteristics are favorable (advantageous) Characteristics are said to be “selected for” Because the environment changes over time, the characteristic that is more __________ for a population changes Therefore, characteristics of the population change, or evolution occurs GENETIC VARIATION 1. Why is genetic variation in a population important? • A population without much variation limits a species’ ability to further _________. (Variation is one of the 4 factors required for natural selection to cause evolution) • If populations do not adapt to their environment, they may become ____________. 2. What are the sources of genetic variation in a population? 1. Sexual reproduction A. Meiosis – one copy of a gene is passed on from each ___________, combination may be different than someone else B. Random fertilization – only one of the millions of sperm involved in mating will fertilize the egg. 2. Mutations: Mutation means a change in _________A sequence. - Can happen when DNA is copied during cellular replication A new DNA sequence can result in new variation (not always). – Many mutations produce traits that are ____________ (e.g. Huntington’s disease) – Some mutations produce traits that are neutral (neither helpful nor harmful) – Very, very few mutations produce traits that are ________________ Natural Selection: • Individuals with advantageous genes survive to reproduce and pass on these genes to their offspring. • Individuals without advantages genes do not survive to reproduce, and these genes do not get passed on in the population. • “Survival of the Fittest” – best _____ (able to survive and reproduce) in the environment • Natural Selection leads to ______________!!! Conclusion: • Mutation does NOT ____________ evolution – it is only a source of variation (just one of the factors required for natural selection) • Natural selection determines if the frequency of traits will change within a population. • Change in traits in a population = __________________ Name________________________ THEORY, HYPOTHESIS, AND PREDICTION (SCIENTIFIC PROCESS) Hypothesis- Prediction- Theory- How are predictions used to test hypotheses? What is the relationship between a hypothesis and a theory? EVIDENCE FOR THE THEORY OF EVOLUTION 6 areas of evidence for evolution: 1. Fossils- 2. Vestigial structures- 3. Biogeography- 4. Homologous structures- 5. Embryology- 6. DNA/protein sequences (macromolecules)- Determining the age of fossils: Relative dating- Radiometric dating- Half-life-