Natural Selection © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

The Process of Natural Selection In any population of individuals, there is genetic variation. Genetic variation is the result of mutation and recombination. In a given environment, some variations of traits are lethal, some make no difference, and some increase or decrease the chance for survival. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

If the environment changes, some individuals might have one or more variations that increase their chance for survival. Organisms with the variation(s) are more likely to survive, reproduce, and pass the favorable variation on to their offspring. Over time, the population changes as more individuals within it have the selected trait. This is called natural selection because it occurs through natural processes. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

The Factors Involved in the Process of Natural Selection 1.Genetic variation from mutation and recombination of genes (made up of DNA) during meiosis. 2.Time 3.Selection, based on the environment, of individuals with the trait that allows for increased survival in the environment. 4.Those with the selected trait reproduce and pass on the trait that allows for survival of the offspring. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

Darwinian Evolution (Natural Selection) Giraffes with longer necks tend to reach leaves more easily. Longer-necked giraffes are more likely to eat enough to survive and reproduce. The offspring inherit their parents’ longer necks. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

A Phrase to Summarize Darwin’s theory of natural selection can be summarized as: Common ancestry and descent with modification. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

Is Evolution by Natural Selection Random? Overall, no. Evolution requires ~Variation due to mutation and recombination AND ~Selection of specific variations. The effect of natural selection on survival of organisms is NOT random. However, some of the events that may lead to mutation can be random: –Mutations can occur in any part of a gene. –Whether a mutation occurs at all is random.

An Example of Mutation and Natural Selection View the following segment on sickle cell disease and malaria: © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

In your science notebook: Explain why individuals who carry one copy of the mutated allele for abnormal hemoglobin are selected for in the natural selection of some human populations. Explain why genetic variation is important in human populations that are exposed to new diseases, which are a type of change in the environment. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.

More on Mutation Remember from genetics that humans have two copies of every gene. Sickle Cell Disease: Two copies of the mutated disease gene (homozygous state) of sickle cell disease can be fatal. However, people with one copy of the mutated disease gene (heterozygous) have an advantage in areas where there is malaria. The heterozygous condition is selected for. © 2008 Regents of the University of California. All rights reserved. Use for SGI Field Test only.