Post on 30-Jun-2020
Lesson OverviewLesson Overview17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation
ANDAND
17.2 Evolution as Genetic 17.2 Evolution as Genetic Change in PopulationsChange in Populations
Lesson OverviewLesson Overview Evolution as Genetic Change in PopulationsEvolution as Genetic Change in Populations
Question #1Natural selection : Phenotype or Genotype?
Natural selection acts directly on phenotype
Natural 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 phenotypes of other individuals
The better-suited individuals produce more offspring than the less fit individuals do
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Question #2Natural 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).
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Question #2Natural 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) in their environment, passing those variations to the next generation.
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Question #2Natural 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) in their environment, passing those variations to the next generation.
(3) Over time, offspring with certain variations (dark fur) make up most of the population.
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Question #3If dogs could only eat deer
Most likely, smaller dogs would die off (because they cannot obtain the food they need), and the bigger ones would survive and reproduce
After a while, instead of a population of dogs of all sizes, most of the dogs in the population would be big dogs
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Question #4Natural Selection
A
1
4
2
3
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
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Question #5What is a gene pool?
All of the genes, including all the different alleles for each gene, that are present in a population
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Question #6What is allele frequency?
The number of times an allele occurs in a gene pool compared to the total number of alleles in that gene pool for the same gene
The percent of a specific allele
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Question #7Define evolution in genetic terms
A change in the frequency of alleles in a population over time
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Question #8Do populations or individuals evolve? Explain.
Populations evolve
Natural selection operates on individual organisms, but the changes it causes in allele frequency show up in the changes 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 and reproduce – however, within its lifetime, it cannot evolve a new phenotype in response to its environment
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Question #9Three main sources of genetic variation
Mutations� A mutation is any change in the genetic material of a cell (some
mutations will affect the fitness of the organism)
� Mutations matter in evolution only if they can be passed from generation
to generation (occur in the germ line cells)to generation (occur in the germ line cells)
Genetic Recombination� This occurs during sexual reproduction based on how the chromosomes
line up during meiosis and also from crossing over
Lateral Gene Transfer� The passing of genes from one individual to another, or even from
individuals of one species to another, that is not its offspring (organsims
pick up “new” genes)
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Question #10Range of phenotypes for single-gene vs. polygenic traits
Single-gene traits have just a few distinct phenotypes
Polygenic traits have many possible phenotypes, which often are not clearly distinct from one anotherare not clearly distinct from one another
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Question #11Student 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 mean they 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 same height
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Question #12How does natural selection affect single-gene traits?
Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to changes in phenotype frequencies
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Question #13How does natural selection affect polygenic traits?
Natural selection on polygenic traits can affect the relative fitness of phenotypes and thereby produce one of three types of selection: directional, stabilizing, or disruptive selectionselection
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Question #14Directional Selection
When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end of the curve
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Question #15Stabilizing Selection
When individuals near the center of the curve have higher fitness than individuals at either end of the curve
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Question #16Disruptive Selection
When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve
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Question #17What is genetic drift?
The random change in allele frequency caused by a series of chance occurrences that cause an allele to become more or less common in a population
Another source of evolutionary change
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Question #18Bottleneck Effect and the Founder Effect
Both are forms of genetic drift (both are random changes in allele frequency of a population)
The bottleneck effect is genetic drift following a dramatic The bottleneck effect is genetic drift following a dramatic reduction in the size of a population
The founder effect is genetic drift as a result of the migration of a small subgroup of a population
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Question #19Genetic Equilibrium
Situation in which allele frequencies in a population remain the same
Genetic equilibrium can be disrupted by…Genetic equilibrium can be disrupted by…
� Nonrandom mating (certain traits will be selected for)
� Small population size (greatly affected by genetic drift)
� Immigration or emigration
� Mutations
� Natural selection