Exam (elaborations)
BIO 182 EXAM 2 QUESTIONS AND ANSWERS
- Course
- Institution
BIO 182 EXAM 2 QUESTIONS AND ANSWERS
[Show more]
Content preview
BIO 182 EXAM 2 QUESTIONS AND ANSWERSHow many modes of selection are there?
3
What are the modes of selection?
Stabilizing selection, directional selection, and disruptive selection
Stabilizing Selection
The mean of the trait remains similar over time but the standard deviation
decreases
Directional Selection
The mean phenotype shifts in a particular direction
Disruptive Selection
The standard deviation of the trait increases as individuals with the mean value
disappear.
Stabilizing Selection Explained
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
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
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
individuals choose to mate only with similar-looking individuals. This non-random mating
prevents recombination from restoring intermediate phenotypes.
Evolution by Natural Selection
Heritable variation leads to differential reproductive success
Selection and Fitness
Directional Selection Equation
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.
False, it would increase the value of the trait over time
Stabilizing Selection Equation
, 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.
True, depends on how large the parameter is for the squared term
What is fitness?
The relative number of viable, fertile offspring
What does natural selection do?
Natural selection not only changes mean phenotypes but also increases or decreases
deviations from mean phenotypes.
What type of selection is most common?
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.
True
True or False? Stabilizing selection occurs more often than disruptive selection.
False
The next 5 questions are based on the following story:
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.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller GEEKA. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $12.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
79650 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now