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Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory
Discuss the validity of the following statement:
When scientists speak of evolutionary theory, the word
“theory” has the same meaning as it does in everyday
language, referring to the fact that evolutionary theory is
just an idea that is not proven and backed by scientific
evidence.
Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory
Consider the validity of the following statement and then
select a correct answer from the options given:
When scientists speak of evolutionary theory, the word
“theory” has the same meaning as it does in everyday
language, referring to the fact that evolutionary theory is
just an idea that is not proven and backed by scientific
evidence.
a. True
b. False
c. I don’t understand the question.
Concept 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Random Mating Result
in Evolution
Discuss the following scenarios with reference to whether or not they
correctly describe examples of the process we attribute to having
been first described by Charles Darwin - evolution by “natural
selection”:
• The development of a curved back over the period of your
lifetime
• Giraffes’ necks lengthening during their lifetime as they reach up
to high branches to eat the leaves of trees
• A drought affects an island where a population of a particular
finch species lives. The species naturally has a small amount of
variability in bill (beak) size. The drought results in finches with
larger bills surviving at a greater rate than those with smaller
bills, since the larger billed birds can crack open and eat very
tough seeds that the small billed individuals cannot.
• A mutation in an insect results in increased digestive efficiency
that allows females to obtain more energy from their food, and
convert that energy into larger eggs that are more likely to
survive, resulting in these females producing more surviving
offspring
Concept 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Random Mating Result
in Evolution
Which of the following scenarios correctly describe examples of the process we
attribute to having been first described by Charles Darwin - evolution by
“natural selection”:
a. The development of a curved back over the period of your lifetime
b. Giraffes’ necks lengthening during their lifetime as they reach up to high
branches to eat the leaves of trees
c. A drought affects an island where a population of a particular finch
species lives. The species naturally has a small amount of variability in
bill (beak) size. The drought results in finches with larger bills surviving
at a greater rate than those with smaller bills, since the larger billed
birds can crack open and eat very tough seeds that the small billed
individuals cannot.
d. A mutation in an insect results in increased digestive efficiency that
allows females to obtain more energy from their food, and convert that
energy into larger eggs that are more likely to survive, resulting in these
females producing more surviving offspring
e. Both c and d
Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies
Consider and discuss the following scenarios in relation to
Hardy–Weinberg equilibrium, and determine whether or
not allele frequencies are likely to change, leading to
evolution:
• An isolated and highly endangered population of 50
woodland caribou
• A large population of lizards whose males have red,
blue, or green tails; females preferentially mate with
red-tailed males
• A large population of fish in an isolated lake; every 5
years a flood results in some fish from a population in
an adjacent lake mixing with this population
Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies
In which of the following scenarios are allele frequencies
are likely to change, leading to evolution, according to
Hardy–Weinberg assumptions:
a. An isolated and highly endangered population of 50
woodland caribou
b. A large population of lizards whose males have red,
blue, or green tails; females preferentially mate with
red-tailed males
c. A large population of fish in an isolated lake; every 5
years a flood results in some fish from a population in
an adjacent lake mixing with this population
d. All of the above
e. None of the above
Concept 15.4 Selection Can Be Stabilizing, Directional, or Disruptive
A flock of 150 tiny orange and brown sparrows is blown off
course and ends up on a huge island where there is a lot
of open shrubby land adjacent to low hills with trees.
There are mammals, many plants, some insects, lizards,
and a few hawks, but there are no other small birds.
There are two types of plants with seeds edible for the
sparrows: a small-seeded tree and a large-seeded bush.
Discuss what you think might happen to this population of
birds over many generations with respect to the three
different types of selection discussed in the text:
• Stabilizing
• Directional
• Disruptive
Concept 15.4 Selection Can Be Stabilizing, Directional, or Disruptive
What you think might happen to this population of birds
over many generations (refer to graphs below)?
a. Stabilizing selection will operate on population beak
size.
b. Directional selection will operate on population beak
size.
c. Disruptive selection will operate on population beak
size.
d. Population beak size will not change; the birds will
maintain their original genetic diversity.
A
B
C
Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
In a population of size N of a diploid organism, the rate of
fixation of neutral mutations () in this population is
given by the equation:
From this equation, discuss what can we deduce about the
influence of population size (N) on the rate of fixation of
neutral mutations in a population.
Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
In a population of size N of a diploid organism, the rate of
fixation of neutral mutations () in this population is
given by the equation:
From this equation, we can deduce that population size (N)
has _______ on the rate of fixation of neutral mutations?
a. an important effect
b. no effect
c. I don’t understand the question.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
Why sex is good
Scientists have long puzzled over why sex has evolved, given the
disadvantages of sex:
1. Gene mixing tends to break up favorable combinations, and why
break up a good thing?
2. Asexual reproduction is twice as efficient as sexual reproduction
at passing on genes to the next generation. Every time a sexual
mother produces a child, only one-half of the child’s genes come
from the mother; the other half are from the father. Reproducing
parthenogenetically, an asexual mother passes on to her child a
complete copy of her genes. It stands to reason that such
populations should rapidly out-reproduce a sexual population,
since every individual is a female that can reproduce offspring.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
Why sex is good (continued)
For these two reasons, it seems clearly disadvantageous for individuals
to reproduce sexually! Yet sex has evolved and some kind of genetic
recombination (sex) occurs and retained in most organisms.
German biologist August Weismann proposed one possible
explanation for this conundrum, suggesting that sex increases
advantageous genetic variation.
When two different individuals mate by joining their gametes together,
they produce a brand new genetic mixture and this promotes
evolutionary adaptation. In other words, sex is good because it
allows you to evolve more quickly when conditions change.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
Why sex is good (continued)
A team of scientists at the Imperial College London investigated the
hypothesis that the genetic recombination that results from sexual
reproduction is advantageous. They published their results in Nature
magazine in March 2005.
They performed an experiment on yeasts, which are single-celled fungi.
Yeasts can reproduce both sexually and asexually, are easy to keep
in the lab, and reproduce rapidly.
Yeasts normally reproduce asexually, but will reproduce sexually when
they are stressed (starved, high temperatures, etc.). The team of
scientists did not want this sexual/asexual switching to occur so they
genetically manipulated one asexual strain. They deleted the two
genes required for normal meiosis, so that sexual reproduction was
impossible. Now they had two pure strains of yeast—an asexual
strain and a sexual strain.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
Why sex is good (continued)
The team compared the reproductive rate of the asexual vs. the sexual
yeasts in two different environments: one benign and one harsh.
• The benign environment had plenty of nutrients although glucose
was limited so that growth was not uncontrolled.
• The harsh environment had the same glucose concentration but
was at a higher temperature and had more demanding osmotic
conditions (e.g., the water was more salty).
Evolutionary “fitness” was measured by comparing the growth rate of
the asexual and sexual strains of yeast.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
On the graph below, plot the results you would expect if Weismann’s
hypothesis were correct. Plot the changes in fitness values over time
in the populations of sexual yeasts in benign conditions, asexual
yeasts in benign conditions, asexual yeasts in harsh conditions, and
sexual yeasts in harsh conditions.
Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result
in New Features
From this graph showing the
experimental results of growing
genetically manipulated sexual and
asexual yeast strains in harsh
versus benign conditions, we can
interpret that:
a. Sexual reproduction is
advantageous in harsh
environments.
b. Asexual reproduction is always
equally advantageous to sexual
reproduction.
c. Asexual reproduction is always
advantageous to sexual
reproduction.
d. There is no difference in fitness
between sexual and asexually
reproducing yeasts.
e. Sexual reproduction is always
advantageous to asexual
reproduction.
Concept 15.7 Evolutionary Theory Has Practical Applications
Discuss the validity of following statements given what you
have learned about evolution:
• Pesticide resistance exhibited by insects in
agricultural settings provides direct evidence that
evolution is occurring.
• Antibiotic resistance is an example of evolution that
helps to keep pharmaceutical companies in business.
• In vitro evolution at the molecular level, as described
in Figure 15.23 of the textbook, is analogous to the
artificial selection of pigeons and dogs that Darwin
was interested in more than two centuries ago.
Concept 15.7 Evolutionary Theory Has Practical Applications
Given what you have learned about evolution, which of the
following statements is true?
a. Pesticide resistance exhibited by insects in
agricultural settings provides direct evidence that
evolution is occurring.
b. Antibiotic resistance is an example of evolution that
helps to keep pharmaceutical companies in business.
c. In vitro evolution at the molecular level, as described
in Figure 15.23 of the textbook, is analogous to the
artificial selection of pigeons and dogs that Darwin
was interested in more than two centuries ago.
d. All of the above
e. None of the above