Lecture Homework #4 Answers
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Orange Coast College *
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Information Systems
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Feb 20, 2024
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Answers and Explanations for Homework #4 BIS 2B Grosberg & Stachowicz Spring 2023 1. Correct Answer: None of the above. Epistasis is when interactions between two or more genes produce a particular phenptype. The example we discussed in class concerned coat color in Labrador retrievers, but there were two loci that interacted, one producinbg pigment (or not), the other whether the pigment (if produced) was brown or black. 2. Correct Answer: 0.2 This question was virtually exactly like the example in the Problem-Solving Discussion. Note that the question states the population is in H-W equilibrium. You can directly calculate the frequencies of the X
1
and X
2
alleles by taking the square root of their respective recessive phenotype frequencies. Since allele frequencies must sum to 1, by subtracting the frequency of X
1
+ X
2
from 1, you will get the frequency of X
3
. 3. Correct answer: None of the above. Because the question said nothing about whether the population was in H-W equilibrium, you could not take the square root of the frequency of the recessive phenotype (frequency of white-flowered plants). There is no way to solve this problem unless either you know the population is in H-W equilibrium, or you know the frequencies of all three genotypes. 4. Correct Answer: If two populations have the same alleles, they will have the same allelic frequencies. All the statements but this one are true. The fact the same two alleles are segregating in different populations says nothing about whether the allelic frequencies in both populations will be the same or different. 5. Correct Answer: Inbreeding or Mutation Inbreeding alone will ONLY change genotypic frequencies (how?), but does not directly affect allelic frequencies. We will also accept mutation as a correct answer, and will re-
grade all of the Homework assignments to make sure that you receive full credit for either answer. 6. Correct Answer: Graph D Graph D is the only graph showing that males with lengthened tails have more nests than those with shorter tails.
7. Correct Answer: The population is in Hardy-Weinberg equilibrium. The question does not say whether the population is in H-W equilibrium. You are just given the Observed genotypic frequencies. Because you know the frequencies of the 3 genotypes, you can easily calculate the frequencies of the S and s alleles. Once you do that, you can then predict the excepted frequencies at H-W equilibrium. Do these expected frequencies differ from those observed in the question? 8. Correct Answer: Each individual pool of breeding salamanders would carry little genetic variation, and would likely have different allelic frequencies than other pools. What major assumption of H-W equilibrium has been violated in scenario? How will violation of this assumption (infinite population size) affect the number of alleles in each population, and how will the expanses of uninhabitable between the remaining pools affect the potential for genetic drift among the pools? 9. Correct Answer: the population Cells and individuals generally do not exhibit genetic variation. Communities and ecosystems consist of populations of species, but it is only the unit of the population within a species that is relevant for measuring and comparing levels of genetic variation. (Would it make sense to compare levels of genetic variation in a plankton species and otters in a coastal community or ecosystem?) 10. Correct Answers: Fitness Function I: B [What form of selection does this fitness function represent? How will it shift the mean and variance of a population for a given trait?] Fitness Function II: C Fitness Function III: A
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