Lesson OverviewLesson Overview
17.1 Genes and Variation17.1 Genes and Variation
17.1 Genes and Variation17.1 Genes and Variation
ANDAND
17.2 Evolution as Genetic 17.2 Evolution as Genetic
Change in PopulationsChange in Populations
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Evolution as Genetic Change in Populations: Lesson Overview, Summaries of Genetics
Natural selection : Phenotype or Genotype? Natural selection acts directly on phenotype. Natural selection acts on an organism's characteristics not.
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Lesson OverviewLesson Overview^ 17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation
ANDAND
17.2 Evolution as Genetic17.2 Evolution as GeneticChange in PopulationsChange in Populations
Question #1 Natural selection : Phenotype or Genotype? Natural selection acts directly on phenotypeNatural selection acts on an organism’s characteristics not
directly on its allelesdirectly on its alleles In any population, some individuals have phenotypes that are
better-suited to their environment than are the phenotypesof other individuals The better-suited individuals produce more offspring than the
less fit individuals do
Question #2 Natural Selection (1)
The mice have variations in fur color (some have white fur (1)
The mice have variations in fur color (some have white fur^ and some have dark fur). (2) Hawks eat mice, and the white mice are easier to spot
when flying overhead – Individuals with certain variations(dark fur) are more likely to survive (they are not seen) intheir environment, passing those variations to the nextgeneration.
Question #2 Natural Selection (1)
The mice have variations in fur color (some have white fur (1)
The mice have variations in fur color (some have white fur^ and some have dark fur). (2) Hawks eat mice, and the white mice are easier to spot
when flying overhead – Individuals with certain variations(dark fur) are more likely to survive (they are not seen) intheir environment, passing those variations to the nextgeneration. (3) Over time, offspring with certain variations (dark fur) make
up most of the population.
Evolution as Genetic Change in PopulationsEvolution as Genetic Change in Populations
Question #4 Natural Selection A
A The cactus has spines which keep the animals from eating it
(also prevents too much water loss) B The cacti survive and reproduce because it has few animals
eating it. The offspring also have spines that protect them,allowing them to mature, and eventually reproduce
Question #5 What is a gene pool? All of the genes, including all the different alleles for each
gene, that are present in a population
Question #7 Define evolution in genetic terms A change in the frequency of alleles in a population over time
Question #8 Do populations or individuals evolve? Explain. Populations evolveNatural selection operates on individual organisms, but the
changes it causes in allele frequency show up in thechanges it causes in allele frequency show up in the population as a whole If an organism has a phenotype that is poorly adapted to its
environment, the organism may be unable to survive andreproduce – however, within its lifetime, it cannot evolve anew phenotype in response to its environment
Question #10 Range of phenotypes for single-gene vs. polygenic traits Single-gene traits have just a few distinct phenotypesPolygenic traits have many possible phenotypes, which often
are not clearly distinct from one anotherare not clearly distinct from one another
Question #11 Student Heights A =
What is the average height for this population? A =
What is the average height for this population? The average height for this population is 170 – 179 cm B =
Jane and Miguel are both 172 cm tall. Does that meanthey have the same genotype? Why or why not? No – because height is a polygenic trait, there are many
different combinations of alleles that result in the sameheight
Question #13 How does natural selection affect polygenic traits? Natural selection on polygenic traits can affect the relative
fitness of phenotypes and thereby produce one of threetypes of selection: directional, stabilizing, or disruptive selectionselection
Question #14 Directional Selection When individuals at one end of the curve have higher fitness
than individuals in the middle or at the other end of thecurve
Question #16 Disruptive Selection When individuals at the outer ends of the curve have higher
fitness than individuals near the middle of the curve
Question #17 What is genetic drift? The random change in allele frequency caused by a series of
chance occurrences that cause an allele to become moreor less common in a population Another source of evolutionary change