Read the introduction below and review relevant information in your textbook.
Complete Preparation tasks 1-4 during week 6. Your responses should completely answer the questions and demonstrate your understanding of the material, and the combined responses should be at least 200 words for full credit.
Complete GenEd tasks 5-9. Your combined responses to Tasks 5-9 should be at least 300 words for full credit. (Most students require 350-450 words to fully respond to these tasks.) Consult the GenEd Project Rubric to make sure your response includes all required elements of the scientific method.
Upload your combined responses to Preparation tasks 1-4 and GenEd tasks 5-9 in a single MS Word document to the Assignment Submission folder. Please review the GenEd Project rubric for detailed expectations as your responses will be evaluated for completeness, content, concepts, comprehension, clarity, and citation. (see GenEd Project rubric)
Introduction with Preparation Tasks:
The mighty yeast, Saccharomyces cerevisiae, or baker’s yeast, is a single-celled member of the kingdom Fungi. For 10,000 years or more, humans have been working with and benefiting from this simple, yet amazing organism.
Yeast are capable of growth using aerobic respiration or anaerobic fermentation, resulting in production of CO2gas and ethanol. These fermentation byproducts have been contributing to leavened bread and the production of beer and wine for thousands of years, but baker’s yeast has a more modern contribution to human technology as well. Some forms of ethanol biofuel are produced using these yeast, and S. cerevisiae has been a star model eukaryote to study central processes in cells. When it comes to basic cell biology, researchers have learned much about human diseases by studying these simple eukaryotes.
Yeast have a somewhat unusual ability to reproduce either sexually using meiosis, or asexually using mitosis, depending on the environment in which they are living.
Preparation Tasks
Preparation Task 1:
Describe the mechanisms by which meiosis would introduce genetic variability in a population. If one diploid yeast cell was heterozygous for an allele with a Dominant mutation on it, what proportion of its offspring could be expected to carry that dominant mutation after mating? (Assume it mates with a cell that is homozygous for the normal, recessive allele.)
Interestingly, yeast switch to sexual reproduction when they are under conditions of stress.
For the purposes of this task, assume yeast populations follow this simplified rule: When yeast are reproducing sexually, they will be found as diploid cells that can go through meiosis (or mitosis), while populations that are producing asexually will include only haploid cells undergoing mitosis. Remember that chromosomes can be counted using karyotypes as seen in your text Figure 9.3.
Preparation Task 2:
Explain why sexual reproduction could be advantageous to a population under stressful conditions. Relate this to the process of natural selection.
Preparation Task 3:
Consider the differences between mitosis and meiosis. Examine the figure “A Simplified Model of Yeast Reproduction” above, and identify ways in which you could determine whether a yeast cell was going through mitosis or meiosis.
Organisms, including yeast, find a variety of environmental conditions stressful. We can grow yeast in a laboratory under either stressful or non-stressful conditions.
Conditions or chemicals that damage organelles (Chapter 3), interfere with transporting nutrients (Chapter 4), or affect the processes of aerobic or anaerobic respiration (Chapter 6) would “stress” these organisms. Environments that affect protein folding (Chapter 2) or enzyme regulation (Chapter 4), are also stressful environments.
Preparation Task 4:
Revisit these sections in your textbook if needed, and propose at least two specific situations or conditions (that you could control) that yeast may find stressful. Include a citation (your textbook or other sources you may consult)
Gen Ed Assignment Tasks
Task 5 Define a problem or pose a question:
Define a question you could investigate that links a stressful scenario you identified in Preparation Task 4 to sexual reproduction in yeast.
Task 6 Formulate a hypothesis:
Formulate a hypothesis that could be tested regarding your question. Include your reasoning that led to this hypothesis.
Task 7 Designing an experiment:
Outline an experiment you could use to test this hypothesis. Include and identify the following 6 key elements of your experiment:
the experimental versus control group
the dependent variable
the independent variable
the standardized variables
adequate replication/sample size
materials and methods
Task 8 Drawing Conclusions:
(Defining results that would support or refute your hypothesis.) Complete both A +B.
A) Describe a possible result from your experiment that would support your hypothesis. You will to describe the results for both the experimental and the control groups to draw a valid conclusion. Provide an explanation for your conclusion. Your explanation should demonstrate the connection between your results and the support of your hypothesis.
B) Describe a possible result from your experiment that would refute your hypothesis. You will to describe the results for both the experimental and the control groups to draw a valid conclusion. Provide an explanation for your conclusion. Your explanation should demonstrate the connection between your results and how they refute your hypothesis.
Task 9 Envision future directions:
Imagine that you have discovered a new species of yeast. Describe how your method, process, or solution could be applicable to this new situation.
The combined responses to all tasks 1-9 must be uploaded to submission folder to receive credit. You will then receive your grade and feedback in the grade book as usual.
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