Investigating Sexual and Asexual Reproduction in Yeast.

U6: GenEd Task Project – Instructions

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Investigating Sexual and Asexual Reproduction in Yeast
Instructions

• 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. At this point, you may want to share your Preparation task 4 with your instructor to make sure you are on the correct track.
• Complete GenEd tasks 5-9. Your combined responses to Tasks 5-9 should be at least300 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 LiveText. 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)
  • Upload a copy of your responses to LiveText to receive credit.

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 product of CO2 gas or 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 Task 1) Describe the mechanisms by which meiosis would introduce genetic variability in a population.

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 Fig 9.3.

Preparation Task 2) Explain why sexual reproduction could be advantageous to a population under stressful conditions.

Preparation Task 3) Consider the differences between mitosis and meiosis. Examine the figure “A simplified model of yeast reproduction,” 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 (Ch 3), interfere with transporting nutrients (Ch 4), or affect the processes of aerobic or anaerobic respiration (Ch 6) would “stress” these organisms. Environments that affect protein folding (Ch 2) or enzyme regulation (Ch 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: Based on the information above and in the figure “A Simplified model of Yeast Reproduction,” define a problem or question you could investigate regarding whether or not yeast are using sexual reproduction in the conditions you identified in Preparation Task 4.

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:

1) the experimental versus control group

2) the dependent variable

3) the independent variable

4) the standardized variables

5) adequate replication/sample size

6) materials and methods.

Task 8 Drawing Conclusions (Defining results that would support or refute your hypothesis.)Complete both A +B)

1. 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 groupsto draw a valid conclusion. Provide an explanation for your conclusion. Your explanation should demonstrate the connection between your results and the supportof your hypothesis.
2. B) Describe a possible result from your experiment that would refuteyour hypothesis. You will to describe the results for both the experimental and the control groupsto 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.

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