1.CHP 17 evolution of
population
2. lesson 1: genes and
variation
Key
3. genetics joins evolutionary theory
5. Researchers discovered that heritable traits are controlled
by genes that are carried on chromosomes. They learned
how changes in genes and chromosomes generate variation.
4. Genotypes and phenotype in evolution
Alleles 5. Typical plants and animals contain two sets of genes, one
contributed by each parent.
5. Specific forms of a gene, called alleles, may vary from
individual to individual.
Genotypes and phenotypes 5. An organism’s genotype is the particular combination of
alleles It carries.
5. Phenotypes include all physical, physiological, and
behavioral characteristics for an organism, such as eye color
and height.
Gene
pool
Allele
frequency
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4. Populations and genes
5. Consist of all genes, including all the different alleles for
each gene that are present in a population.
5. Researchers study gene pools by examining the number
of different alleles it contains.
5. Is the number is times an allele occurs in a gene pool,
compared to the total number of alleles in that pool for the
same gene.
5. A population is group of individuals of the same species
that mate and produce offspring.
5. Evolution, in genetic terms, involves a change in the
frequency of alleles in a population over time.
3. sources of genetic variation
5. Three sources of genetic variations are (1) mutations, (2)
genetic recombination during sexual reproduction, and (3)
lateral gene transfer.
Mutations 5. A mutation is any change in the genetic material of a cell.
5. some mutations involve changes within individual genes
3. lateral gene transfer
5. Lateral gene transfer can increase genetic variations in
any species that picks up the “new” genes.
5. Lateral gene transfer has been a common, and important,
in single-celled organisms during the history of life.
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Single gene
3. Single gene and polygenic traits
5. The number of phenotypes produced for a trait depends
on how many genes control the trait.
Single gene traits
5. A trait controlled by only one gene.
traits
Polygenic
4. Polygenic traits
5. Many traits are controlled by two or more genes.
traits
5. Each gene of a polygenic trait often has two or more
alleles.
5. Height in humans is one example of a polygenic trait.
2. lesson 2: evolution as genetic
change in population
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3. How natural selection works
4. natural selection on single-gene traits
5. Natural selection on single-gene traits can lead to changes
in allele frequencies and, thus, to change in phenotype
frequencies.
5. like a lizard population changing its color to its
surroundings over time for an advantage.
4. Natural Selection on polygenic traits
Natural selection on polygenic duce one of three types of
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selection: (1) directional selection, (2) stabilizing selection,
(3) disruptive selection.
Directional selection 5. When individuals at one end of the curve have higher
fitness than individuals in the middle or at the other end.
5. The range of phenotypes shifts because some individuals
are more successful at surviving and reproducing than are
others.
Stabilizing
5. When individuals near the center of the curve have higher
selection
fitness than individuals at either end.
5. This situation keeps the center of the curve at its current
position, but it narrows the curve overall.
Disruptive
5. When individuals at the outer ends of the curve have
selection
higher fitness than individuals in the middle of the curve.
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3. Genetic drift
5. In small populations, individuals that carry a particular
allele may leave more descendants than others, just by
chance. Over time, a series of chance occurrences can cause
an allele to become more or less common in a population.
Genetic drift 5. Random change in allele frequency.
Genetic
bottlenecks
The founder effect
Genetic
equilibrium
4. Genetic bottlenecks
5. Is a change in allele frequency following a dramatic
reduction in the size of a population.
5. A severe bottleneck effect can sharply a population’s
genetic diversity.
4. The founder effect
5. When allele frequencies change as a result of the
migration of a small subgroup of a population.
5. One example of the founder effect is the evolution of
several hundred species of fruit flies on different Hawaiian
islands.
3. Evolution versus Genetic equilibrium
5. If a population is not evolving, allele frequencies in its
gene pool do not change, which means that the population is
in genetic equilibrium.
4. Sexual reproduction and allele frequency
5. Gene shuffling during sexual reproduction produces
many gene combinations.
5. Researchers realized that meiosis and fertilization, by
themselves, do not change allele frequencies.
5. A population of sexually reproducing organisms could
remain in genetic equilibrium.
4. The Hardy-Weinberg principle
Hardy-Weinberg principle 5. States that allele frequency in a population should remain
constant unless one or more factors cause those frequencies
to change.
5. Here’s how it works- suppose that there are two alleles
for a gene: A(dominant) and a(recessive). A cross of these
alleles can produce three possible genotypes: AA, Aa, and
aa.
key 5. The Hardy-Weinberg principle predicts that five
conditions can disturb genetic equilibrium to occur: (1)
nonrandom mating; (2) small population size; and (3)
immigration or emigration; (4) mutations; or (5) natural
selection.
Nonrandom mating
5. In many species, individuals select mates based on
Sexual selection
heritable traits, such as size, strength, or coloration, a
practice known as sexual selection.
Small population size
5. Genetic drift can affect small populations strongly.
5. Evolutionary change due to genetic drift thus happens
more easily in small populations.
Immigration or
emigration
5. Individuals who join a population may introduce new
alleles into the gene pool, and individuals who leave may
remove alleles. Thus, any movement of individuals into
(immigration) or out of (emigration) a population can
disrupt genetic equilibrium, a process called gene flow.
Mutations
Natural selection
5. Mutations can introduce new alleles into a gene pool,
thereby changing allele frequencies and causing evolution to
occur.
5. If different genotypes have different fitness, genetic
equilibrium will be disrupted, and evolution will occur.
2. lesson 3: the process of
speciation
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3. Isolating mechanisms
5. When population becomes reproductively isolated, they
can evolve into two separate species. Reproductive isolation
can develop in a variety of ways, including behavioral
isolation, geographic isolation, and temporal isolation.
Species 5. A population or group of populations whose members can
interbreed and produce fertile offspring.
speciation 5. The formation of a new species.
Reproductive isolation 5. Once a population has thus split into two groups, changes
in one of those gene pools cannot spread to the other.
Because these two groups no longer interbreed, reproductive
isolation has occurred.
Geographic
isolation
4. Geographic isolation
5. When two populations are separated by geographic
barriers such as rivers, mountains, or bodies of water
geographic isolation occurs.
4. Behavioral isolation
Behavioral isolation 5. Suppose two populations that are capable of interbreeding
develop differences in courtship rituals or other behaviors.
5. For example, eastern and western meadowlarks are
similar birds whose habitats overlap.
5. Eastern meadowlarks don’t respond to western
meadowlarks songs, and vice versa.
Temporal isolation
4. Temporal isolation
5. A third isolating mechanism known as temporal isolation
happens when two or more species reproduce at different
times.
3. Speciation in Darwin’s finches
5. According to this hypothesis, speciation in Galapagos
finches occurred by founding of a new population,
geographic isolation, changes in the new populations gene
pool, behavioral isolation, and ecological competition.
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2. lesson 4: Molecular
evolution
3. Timing linage splits: Molecular clocks
key 5. A molecular clock uses mutation rates in DNA to
estimate the time that two species have been evolving
independently.
Molecular clock 5. is used to compare stretches of DNA to mark the passage
of evolutionary time.
4. Neutral mutations as “ticks”
5. To understand molecular clocks, think about oldfashioned pendulum clocks. They mark time with a
swinging pendulum. A molecular clock also relies on a
repeating process to mark time—mutations.
4. Calibrating the clock
5. The use of molecular clocks is not simple, because is not
just one molecular clack in a genome. There are many
different clocks, each of which “ticks” at a different rate.
This is because some genes accumulate mutations faster
than others.
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3. Gene duplication
5. Modern genes probably descended from a much smaller
number of genes in the earliest life forms.
5. One way in which new genes evolve is though the
duplication, and then modification of existing genes.
4. copying genes
5. Most organisms carry several copies of various genes.
Sometimes organisms carry two copies of the same gene
and others carry thousands.
Gene families 4. Gene families
5. Multiple copies of a duplicated gene can turn into a group
of related genes called a gene family.
5. Members of a gene family typically produce similar, yet
slightly different, proteins.
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4. Hox genes and evolution
5. Small changes in hox gene activity during embryological
development can produce large changes in adult animals.
5. For example, insects and crustaceans are related to
ancient common ancestors that possesses dozens of legs.