BIO 182 Exam 2 Exam Question And
Answers 2024
How many modes of selection are there? - correct answers✅3
What are the modes of selection? - correct answers✅Stabilizing selection,
directional selection, and disruptive selection
Stabilizing Selection - correct answers✅The mean of the trait remains similar over
time but the standard deviation decreases
Directional Selection - correct answers✅The mean phenotype shifts in a particular
direction
Disruptive Selection - correct answers✅The standard deviation of the trait
increases as individuals with the mean value disappear.
Stabilizing Selection Explained - correct answers✅The stronger the selective
pressure against extreme phenotypes, the narrower the distribution of phenotypes
will be in future generations. In the end, the size of the standard deviation will
reflect both the strength of selection against extremes and the frequency of
mutations creating new variation. Thus, when we observe a wide range of
phenotypes in a population, we might infer weak selective pressure against the
extremes.
Directional Selection Explained - correct answers✅The population's environment
changes. The mean phenotype in the population may no longer be the phenotype
that reproduces the most. Over time, we should expect the mean phenotype to shift
higher or lower, depending on the direction of selective pressure. Once the mean
phenotype catches up to the change in the environment, stabilizing selection will
resume. The environment must change slowly enough for the population to persist.
If the environment changes too quickly, no members of the population will be able
to reproduce, leading to extinction.
Disruptive Selection Explained - correct answers✅A population can occupy an
environment in which individuals with extreme phenotypes reproduce more than
individuals with the mean phenotype.
This mode of selection occurs when several distinct strategies confer greater
reproductive success than other strategies do. Can produce new species when
,BIO 182 Exam 2 Exam Question And
Answers 2024
individuals choose to mate only with similar-looking individuals. This non-random
mating prevents recombination from restoring intermediate phenotypes.
Evolution by Natural Selection - correct answers✅Heritable variation leads to
differential reproductive success
Selection and Fitness - correct answers✅
Directional Selection Equation - correct answers✅y=bx+c
y=relative fitness
x= trait value
b= strength of selection
c=parameter
True or False? If the slope of the relationship between the phenotype and fitness is
positive, natural selection would decrease the phenotype over generations. -
correct answers✅False, it would increase the value of the trait over time
Stabilizing Selection Equation - correct answers✅y=ax^2+bx+c
y=relative fitness
x= trait value
a/b= strength of selection
c= parameter
True or False? If the parameter for the squared term is negative, natural selection
will likely stabilize the phenotype at an intermediate value. - correct
answers✅True, depends on how large the parameter is for the squared term
What is fitness? - correct answers✅The relative number of viable, fertile offspring
, BIO 182 Exam 2 Exam Question And
Answers 2024
What does natural selection do? - correct answers✅Natural selection not only
changes mean phenotypes but also increases or decreases deviations from mean
phenotypes.
What type of selection is most common? - correct answers✅All three can happen
to some extent. Both the direction and the strength of natural selection varies
greatly among traits and species.
True or False? Directional selection is more likely to be weak than strong. - correct
answers✅True
True or False? Stabilizing selection occurs more often than disruptive selection. -
correct answers✅False
The next 5 questions are based on the following story: - correct answers✅A
researcher studied the relationship between the phenotypes of snakes and their
fitness. First, he measured the color patterns and the escape behavior of hundreds
of snakes. For color pattern, snakes were scored as being either checkered or
striped (see photos below). For escape behavior, snakes were chased by simulating
a predator attack; some snakes moved in a straight line while fleeing, but others
tended to turn frequently. After recording these phenotypes, the researcher released
the snakes in their natural environment. A year later, he returned to see which
snakes had survived. The survival of snakes was used as a proxy of fitness. The
figure below shows the relationships between color pattern and relative fitness for
snakes that flee straight and snakes that flee by turning.
1. A snake with stripes would be more likely to survive by fleeing predators in a
straight line. (T/F) - correct answers✅True
2. Regardless of escape behavior, the color pattern of snakes will be influenced by
directional selection. (T/F) - correct answers✅True
3. Over many generations, the population of snakes should evolve toward striped
snakes that flee by turning or checkered snakes that flee straight. (T/F) - correct
answers✅False
Answers 2024
How many modes of selection are there? - correct answers✅3
What are the modes of selection? - correct answers✅Stabilizing selection,
directional selection, and disruptive selection
Stabilizing Selection - correct answers✅The mean of the trait remains similar over
time but the standard deviation decreases
Directional Selection - correct answers✅The mean phenotype shifts in a particular
direction
Disruptive Selection - correct answers✅The standard deviation of the trait
increases as individuals with the mean value disappear.
Stabilizing Selection Explained - correct answers✅The stronger the selective
pressure against extreme phenotypes, the narrower the distribution of phenotypes
will be in future generations. In the end, the size of the standard deviation will
reflect both the strength of selection against extremes and the frequency of
mutations creating new variation. Thus, when we observe a wide range of
phenotypes in a population, we might infer weak selective pressure against the
extremes.
Directional Selection Explained - correct answers✅The population's environment
changes. The mean phenotype in the population may no longer be the phenotype
that reproduces the most. Over time, we should expect the mean phenotype to shift
higher or lower, depending on the direction of selective pressure. Once the mean
phenotype catches up to the change in the environment, stabilizing selection will
resume. The environment must change slowly enough for the population to persist.
If the environment changes too quickly, no members of the population will be able
to reproduce, leading to extinction.
Disruptive Selection Explained - correct answers✅A population can occupy an
environment in which individuals with extreme phenotypes reproduce more than
individuals with the mean phenotype.
This mode of selection occurs when several distinct strategies confer greater
reproductive success than other strategies do. Can produce new species when
,BIO 182 Exam 2 Exam Question And
Answers 2024
individuals choose to mate only with similar-looking individuals. This non-random
mating prevents recombination from restoring intermediate phenotypes.
Evolution by Natural Selection - correct answers✅Heritable variation leads to
differential reproductive success
Selection and Fitness - correct answers✅
Directional Selection Equation - correct answers✅y=bx+c
y=relative fitness
x= trait value
b= strength of selection
c=parameter
True or False? If the slope of the relationship between the phenotype and fitness is
positive, natural selection would decrease the phenotype over generations. -
correct answers✅False, it would increase the value of the trait over time
Stabilizing Selection Equation - correct answers✅y=ax^2+bx+c
y=relative fitness
x= trait value
a/b= strength of selection
c= parameter
True or False? If the parameter for the squared term is negative, natural selection
will likely stabilize the phenotype at an intermediate value. - correct
answers✅True, depends on how large the parameter is for the squared term
What is fitness? - correct answers✅The relative number of viable, fertile offspring
, BIO 182 Exam 2 Exam Question And
Answers 2024
What does natural selection do? - correct answers✅Natural selection not only
changes mean phenotypes but also increases or decreases deviations from mean
phenotypes.
What type of selection is most common? - correct answers✅All three can happen
to some extent. Both the direction and the strength of natural selection varies
greatly among traits and species.
True or False? Directional selection is more likely to be weak than strong. - correct
answers✅True
True or False? Stabilizing selection occurs more often than disruptive selection. -
correct answers✅False
The next 5 questions are based on the following story: - correct answers✅A
researcher studied the relationship between the phenotypes of snakes and their
fitness. First, he measured the color patterns and the escape behavior of hundreds
of snakes. For color pattern, snakes were scored as being either checkered or
striped (see photos below). For escape behavior, snakes were chased by simulating
a predator attack; some snakes moved in a straight line while fleeing, but others
tended to turn frequently. After recording these phenotypes, the researcher released
the snakes in their natural environment. A year later, he returned to see which
snakes had survived. The survival of snakes was used as a proxy of fitness. The
figure below shows the relationships between color pattern and relative fitness for
snakes that flee straight and snakes that flee by turning.
1. A snake with stripes would be more likely to survive by fleeing predators in a
straight line. (T/F) - correct answers✅True
2. Regardless of escape behavior, the color pattern of snakes will be influenced by
directional selection. (T/F) - correct answers✅True
3. Over many generations, the population of snakes should evolve toward striped
snakes that flee by turning or checkered snakes that flee straight. (T/F) - correct
answers✅False
