Download Lesson Overview - Enfield High School

Lesson Overview
17.1 Genes and Variation
AND
17.2 Evolution as Genetic
Change in Populations
Lesson Overview
Evolution as Genetic Change in Populations
Question #1
Natural selection : Phenotype or Genotype?
Natural selection acts directly on phenotype
Natural selection acts on an organism’s characteristics not
directly 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
Lesson Overview
Evolution as Genetic Change in Populations
Question #2
Natural Selection
(1) The mice have variations in fur color (some have white fur
and some have dark fur).
Lesson Overview
Evolution as Genetic Change in Populations
Question #2
Natural Selection
(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.
Lesson Overview
Evolution as Genetic Change in Populations
Question #2
Natural Selection
(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.
Lesson Overview
Evolution as Genetic Change in Populations
Question #3
If 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
Lesson Overview
Question #4
Evolution as Genetic Change in Populations
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Natural Selection
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
Lesson Overview
Evolution as Genetic Change in Populations
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
Lesson Overview
Evolution as Genetic Change in Populations
Question #6
What 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
Lesson Overview
Evolution as Genetic Change in Populations
Question #7
Define evolution in genetic terms
A change in the frequency of alleles in a population over time
Lesson Overview
Evolution as Genetic Change in Populations
Question #8
Do 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
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
Lesson Overview
Evolution as Genetic Change in Populations
Question #9
Three 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)
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)
Lesson Overview
Evolution as Genetic Change in Populations
Question #10
Range 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 another
Lesson Overview
Evolution as Genetic Change in Populations
Question #11
Student Heights
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
Lesson Overview
Evolution as Genetic Change in Populations
Question #12
How 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
Lesson Overview
Evolution as Genetic Change in Populations
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 three
types of selection: directional, stabilizing, or disruptive
selection
Lesson Overview
Evolution as Genetic Change in Populations
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 the
curve
Lesson Overview
Evolution as Genetic Change in Populations
Question #15
Stabilizing Selection
When individuals near the center of the curve have higher
fitness than individuals at either end of the curve
Lesson Overview
Evolution as Genetic Change in Populations
Question #16
Disruptive Selection
When individuals at the outer ends of the curve have higher
fitness than individuals near the middle of the curve
Lesson Overview
Evolution as Genetic Change in Populations
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 more
or less common in a population
Another source of evolutionary change
Lesson Overview
Evolution as Genetic Change in Populations
Question #18
Bottleneck 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
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
Lesson Overview
Evolution as Genetic Change in Populations
Question #19
Genetic Equilibrium
Situation in which allele frequencies in a population remain
the same
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