Evolution natural selection and phenotypes
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Evolution: Natural Selection and Phenotypes. Big Idea 1: Process of evolution drives the diversity of life. Essential Knowledge. 1A1: Natural selection is a major mechanism of evolution. 1A2: Natural selection acts on phenotypic variations.

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Evolution: Natural Selection and Phenotypes

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Evolution: Natural Selection and Phenotypes

Big Idea 1: Process of evolution drives the diversity of life

Essential Knowledge

  • 1A1: Natural selection is a major mechanism of evolution.

  • 1A2: Natural selection acts on phenotypic variations.

  • 1A3: Evolutionary change is also driven by random processes


  • Change in genetic makeup of a population over time.

  • Natural selection is its major driving mechanism.

What do you know about this guy?

Darwin said…

  • Competition for limited resources results in differential survival.

What’s wrong with this picture though???

Natural Selection

  • Individs w/ more favorable phentoypes (physical features) are more likely to survive and produce more offspring, passing down traits to subsequent generations!

Describe Pandy’s phenotype

Genetic Code: DNA/RNA

Physical features and Behaviors

Types of Natural Selection

1) Stabilizing Selection: Selective pressures select against the 2 extremes of a trait.

  • Ex: Better to be average!

Types of Natural Selection

2) Directional selection: 1extreme of the trait experiences selection against it.

  • Ex: giraffes w/ short necks

Types of Natural Selection

3) Disruptive selection: Selection pressures act against individuals in middle of 2 extremes of the trait.

  • Ex: Don’t be average

Evolutionary Fitness

  • To be fit, you must be able to reproduce!

  • Measured by reproductive success.

Why is the Zorse Not Evolutionary Fit?

Genetic Variation is Good For You!

  • A diverse gene pool is important for survival of a species in a changing environment.


  • A genetic variation that is favored by selection and provides an advantage to an org. in a environment.

  • Occurs naturally through environmental pressures.

  • Chance and random events (genetic drift) can also influence the evolutionary process, especially for small pops.

What is Going to Happen to this Small Population, thanks to Genetic Drift?

Natural Selection Acts on Phenotype

  • Environments may change and act as a selective mechanism on populations.

Peppered Moth Video Clip

If the environment changes, different genetic variations can be selected in each generation.

Global warming and earlier flowering time

Phenotypic variations occur b/c of random changes (mutations) and new gene combinations (fertilization and meiosis)

Some Phenotypic Variations Increase Fitness

  • Ex: Sickle cell anemia (Ss) makes you far less likely to die from malaria. Heterozygote advantage.

Whose fitness will be decreased?

Humans Impact Variation

  • Often times decreasing it…food crops have been artificially selected to be genetically similar.

Wooly Worm Lab

  • Natural Selection and Chi Square Test!

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