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100
According to the first section of the paper, what is often the primary obstacle to the evolution of outcrossing?
The cost of males (males do not directly produce offspring).
100
What was the mutagen ethyl methanesulfonate (EMS) used for in the experiment?
EMS was used to induce a higher than normal mutation rate in some of the worms.
100
What happened to the number of individuals who reproduced by outcrossing in the wild type group as mutation rates were increased/mutagen was added?
The number of outcrossing individuals increased.
100
Outcrossing enables a stronger and faster response to environmental changes than does selfing. Does the data in this study support this conclusion?
True/yes
100
In the (control, mutated, both, neither) populations, the rate of adaptation decreased over time in outcrossing populations. Hint: refer to figure 1a.
Neither, there was an increase in the rate of adaptation for both the control and mutated groups.
200
What are the three different types of worms used in this experiment? Hint: one type is obligate selfing.
1. Worms that only reproduce through selfing. 2. Worms that only reproduce through outcrossing. 3. Worms that are wild type and can use both methods of reproduction.
200
What are the two environments in which worms were tested in the experiment?
1. Presence of elevated mutation rates and migratory barrier. 2. Presence of a pathogenic bacteria.
200
Free Space
Free Space
200
After exposure to S. marcescens, the wild type populations had a (increase, decrease) in the rate of outcrossing.
Increase
200
Overall, (outcrossing, selfing) allows a more rapid adaptation to ecological change.
Outcrossing
300
What are the two hypotheses regarding why outcrossing occurs as a reproductive method in nature despite its disadvantages?
1. Outcrossing allows organisms to more adequately and quickly adapt to a changing environment. 2. Through the possibility of genetic recombination, outcrossing makes it less likely that small deleterious mutations will accumulate.
300
In the experiment, it was found that after increasing the mutation rate, the ______ population of worms was best able to maintain fitness.
Outcrossing
300
In the experiments testing the three types of worms' adaptation rates in the presence of S. marcescens, what was on the control plates?
Heat-killed S. marcescens.
300
What is an evolutionary dead-end?
A trait/characteristic that has evolved that will ultimately result in extinction.
300
Which of the three groups of worms demonstrated the highest rate of adaptation in the experiment with S. marcescens?
The obligate outcrossing worms (worms that only reproduce through outcrossing)
400
According to the paper, why might one initially expect that selfing might be advantageous over outcrossing?
Selfing reproduction avoids the two-fold cost of males because all individuals can bear offspring. Also, unfavorable mutations which are expressed to a high extent can be purged.
400
According to the paper, selfing populations are only good at purging deletrious mutations when the effect of the mutations is (large, small).
Large
400
"Before selection on S. marcescens, the experimental populations were mutagenized with EMS.." What was the purpose of using EMS before plating the worms on S. marcescens?
To create genetic variation in the populations which were previously inbred. (Recall that genetic variation is necessary for natural selection to occur.)
400
What general trend does figure 1a show?
In both the control and mutated groups, as outcrossing rates increase, the relative fitness of the populations also increase.
400
What does figure 1c show about the relationship between adaptation and outcrossing rate?
As the outcrossing rate increases, adaptation rate/fitness also increases.
500
What is inbreeding depression? Why does it occur?
Inbreeding depression is a situation in which the fitness of a population is reduced as a result of inbreeding. It occurs because deleterious alleles have higher chances of accumulating in a population that does not see the introduction of new genetic variations.
500
Why do you think selfing populations cannot effectively purge deletrious mutations that have very small effects on the organism?
If the mutation has only a very small effect, then the organism carrying it will likely survive. When that organism reproduces through selfing, its offspring will also receive this deletrious mutation. As more generations arise, these small mutations can accumulate.
500
What happens to the fitness of obligate selfing populations of C. elegans worms over time when natural mutation rates are maintained?
The fitness will decrease over time, eventually leading to extinction.
500
According to figure 1b, what happens to the rate of outcrossing when there are more mutations in the population?
The rate of outcrossing increases.
500
According to figure 1d, outcrossing rates are generally higher for the populations exposed to S. marcescens. What is the significance of this/what does it tell us about outcrossing as a reproductive method?
Outcrossing is favorable in conditions in which populations must adapt to a novel environment.