Wayne Community College Random Mutation and Selection Discussion Questions
Wayne Community College Random Mutation and Selection Discussion Questions
Mutation is essential for evolutionary processes because it is the ultimate source of genotypic variation – variation that can then be expressed phenotypically. Alterations to the instructions in an Avidian’s genome can affect its ability to perform certain functions and even its ability to reproduce (the phenotypes of Avidians). In this exercise we use Avida-ED to explore the consequences of random mutation generating phenotypic variation that can be under selection in the environment.
Avida-ED provides a way to test whether mutations occur at random, or if mutations are directed to occur in response to natural selection within the environment. In some sense, we are testing directly what Salvador Luria and Max Delbrück (1943) did in their elegant Nobel Prize winning experiments (Luria SE, Delbrück M. 1943. “Mutations of Bacteria from Virus Sensitivity to Virus Resistance.” Genetics 28:491- 511). We also consider a reason why time is fundamental to the process of evolution; if mutations do not generate a phenotype, then that trait cannot evolve in a population.
Phenotypic Variation and Selection
Random mutations create genotypic diversity within a population. In Avida-ED, mutations can allow some Avidians to perform functions. For our purposes we will simply note that these are logic functions involving the comparison of numbers Avidians encounter in their digital environment. In Avida-ED there are nine functions – NOT, NAN, AND, ORN, ORO, ANT, NOR, XOR, EQU; and nine corresponding resources – notose, nanose, andose, ornose, orose, antose, norose, xorose, equose. An Avidian with a particular sequence of instructions can perform a function, but the individual Avidian performing this function is only rewarded if the corresponding resource is available in the environment. For example, the “@ancestor” organism cannot perform any functions, but random mutations over multiple generations might produce a descendant with a genome that codes for one or more functions (e.g., NOT). If the corresponding resource is in the environment (e.g., notose), then this Avidian will have an increased energy acquisition rate and be favored by natural selection within its environment.
Multiple types of variation between individuals in a population are possible. Phenotypes are the observable characteristics of an organism; genotypes are the specific genetic sequences that encode for that individual. In Avida-ED, we define the phenotype of an organism based on which of nine different logic functions the organism can perform. Whether or not the individual can perform the function is the phenotype. If the corresponding resource – which here are the words ending in -ose – is present, that phenotype will be rewarded. But note that, for example, if the organism consumes ornose, it has the ORN+ phenotype; ornose is the resource, and ORN is the function.
Natural selection acts upon phenotypic variation in a population of organisms. Individuals whose phenotypes are better suited to a particular environment tend to have greater reproductive success. For understanding Avidian phenotypes in selective environments, it is illustrative to use an analogy to bacteria processing sugar resources as food. When an individual bacterium is able to metabolize a sugar in its environment, it receives energy to be used for growth and reproduction; bacteria that can metabolize the sugar will be favored due to natural selection. Similarly, when an Avidian is able to perform a function corresponding to a resource in its environment it is rewarded with an increased energy acquisition rate, producing offspring more quickly; Avidians that can perform a function associated with an available resource will be favored due to natural selection. 1 attachmentsSlide 1 of 1
UNFORMATTED ATTACHMENT PREVIEW
Question 1 Question 5.1A. Before we begin the experiment, it is important to consider hypotheses. What are the hypotheses being tested in this experiment? (You may want to refer the Introduction to Random Mutation and Selection.) Question 2 Question 5.1B. How does this experiment test the hypotheses? (You may want to refer to the Activity page on Phenotypic Variation and Selection.) Question 3 Question 5.1C. Do you predict that an Avidian performing NOT will appear sooner in the first treatment when notose is absent in the environment or the second treatment when notose is present? Why? Exercise 5.2 Treatment 1: First Occurrence Of NOT When All Resources Absent (No Notose) 1. In the Population viewer, flip to Setup. 2. Drag “@ancestor” from the Freezer to the Ancestral Organism(s) box. 3. Set the following parameters: Dish Size 30×30; 2%
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Wayne Community College Random Mutation and Selection Discussion Questions
Mutation is essential for evolutionary processes because it is the ultimate source of genotypic variation – variation that can then be expressed phenotypically. Alterations to the instructions in an Avidian’s genome can affect its ability to perform certain functions and even its ability to reproduce (the phenotypes of Avidians). In this exercise we use Avida-ED to explore the consequences of random mutation generating phenotypic variation that can be under selection in the environment.
Avida-ED provides a way to test whether mutations occur at random, or if mutations are directed to occur in response to natural selection within the environment. In some sense, we are testing directly what Salvador Luria and Max Delbrück (1943) did in their elegant Nobel Prize winning experiments (Luria SE, Delbrück M. 1943. “Mutations of Bacteria from Virus Sensitivity to Virus Resistance.” Genetics 28:491- 511). We also consider a reason why time is fundamental to the process of evolution; if mutations do not generate a phenotype, then that trait cannot evolve in a population.
Phenotypic Variation and Selection
Random mutations create genotypic diversity within a population. In Avida-ED, mutations can allow some Avidians to perform functions. For our purposes we will simply note that these are logic functions involving the comparison of numbers Avidians encounter in their digital environment. In Avida-ED there are nine functions – NOT, NAN, AND, ORN, ORO, ANT, NOR, XOR, EQU; and nine corresponding resources – notose, nanose, andose, ornose, orose, antose, norose, xorose, equose. An Avidian with a particular sequence of instructions can perform a function, but the individual Avidian performing this function is only rewarded if the corresponding resource is available in the environment. For example, the “@ancestor” organism cannot perform any functions, but random mutations over multiple generations might produce a descendant with a genome that codes for one or more functions (e.g., NOT). If the corresponding resource is in the environment (e.g., notose), then this Avidian will have an increased energy acquisition rate and be favored by natural selection within its environment.
Multiple types of variation between individuals in a population are possible. Phenotypes are the observable characteristics of an organism; genotypes are the specific genetic sequences that encode for that individual. In Avida-ED, we define the phenotype of an organism based on which of nine different logic functions the organism can perform. Whether or not the individual can perform the function is the phenotype. If the corresponding resource – which here are the words ending in -ose – is present, that phenotype will be rewarded. But note that, for example, if the organism consumes ornose, it has the ORN+ phenotype; ornose is the resource, and ORN is the function.
Natural selection acts upon phenotypic variation in a population of organisms. Individuals whose phenotypes are better suited to a particular environment tend to have greater reproductive success. For understanding Avidian phenotypes in selective environments, it is illustrative to use an analogy to bacteria processing sugar resources as food. When an individual bacterium is able to metabolize a sugar in its environment, it receives energy to be used for growth and reproduction; bacteria that can metabolize the sugar will be favored due to natural selection. Similarly, when an Avidian is able to perform a function corresponding to a resource in its environment it is rewarded with an increased energy acquisition rate, producing offspring more quickly; Avidians that can perform a function associated with an available resource will be favored due to natural selection. 1 attachmentsSlide 1 of 1
UNFORMATTED ATTACHMENT PREVIEW
Question 1 Question 5.1A. Before we begin the experiment, it is important to consider hypotheses. What are the hypotheses being tested in this experiment? (You may want to refer the Introduction to Random Mutation and Selection.) Question 2 Question 5.1B. How does this experiment test the hypotheses? (You may want to refer to the Activity page on Phenotypic Variation and Selection.) Question 3 Question 5.1C. Do you predict that an Avidian performing NOT will appear sooner in the first treatment when notose is absent in the environment or the second treatment when notose is present? Why? Exercise 5.2 Treatment 1: First Occurrence Of NOT When All Resources Absent (No Notose) 1. In the Population viewer, flip to Setup. 2. Drag “@ancestor” from the Freezer to the Ancestral Organism(s) box. 3. Set the following parameters: Dish Size 30×30; 2%
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