Ch. 15 - Recombinant DNA Technology and Its Applications

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 15 - Recombinant DNA Technology and Its Applications

Problem 22b

Chapter 15, Problem 22b

You have identified five genes in S. cerevisiae that are induced when the yeast are grown in a high-salt (NaCl) medium. To study the potential roles of these genes in acclimation to growth in high-salt conditions, you wish to examine the phenotypes of loss- and gain-of-function alleles of each. How would your answer differ if you were working with tomato plants instead of yeast?

Verified step by step guidance

Step 1: Understand the difference in genetic manipulation techniques between yeast (S. cerevisiae) and tomato plants. Yeast is a single-celled organism that can be genetically manipulated relatively easily using techniques like homologous recombination and CRISPR-Cas9. Tomato plants, being multicellular and more complex, require different approaches such as Agrobacterium-mediated transformation or biolistic methods for introducing genetic changes.

Step 2: Consider the growth conditions and experimental setup. Yeast can be grown in controlled liquid media with high-salt conditions, allowing for rapid phenotypic analysis. Tomato plants, on the other hand, require soil or hydroponic systems, and phenotypic analysis may take longer due to their slower growth and development.

Step 3: Account for the differences in gene expression analysis. In yeast, gene expression can be studied using techniques like RNA sequencing or qPCR directly from cultures. In tomato plants, tissue-specific expression must be considered, and samples may need to be collected from specific organs (e.g., leaves, roots) for analysis.

Step 4: Plan for phenotypic evaluation. In yeast, phenotypes such as growth rate or survival in high-salt conditions can be assessed directly in culture. In tomato plants, phenotypes might include changes in growth, leaf morphology, or fruit production under high-salt conditions, requiring more complex observational methods.

Step 5: Adapt the experimental design for genetic studies. Loss-of-function alleles in yeast can be created by gene knockout or deletion, while in tomato plants, RNA interference (RNAi) or CRISPR-Cas9 can be used. Gain-of-function alleles in yeast can be introduced via plasmid overexpression, whereas in tomato plants, transgenic approaches or overexpression constructs integrated into the genome are required.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gene Function and Alleles

Genes are segments of DNA that encode proteins, which perform various functions in an organism. Alleles are different versions of a gene that can result in variations in traits. Understanding loss-of-function alleles (which disrupt gene function) and gain-of-function alleles (which enhance or change gene function) is crucial for studying how specific genes contribute to an organism's response to environmental stressors, such as high salt concentration.

Model Organisms in Genetics

Model organisms, like S. cerevisiae (yeast) and tomato plants, are species widely used in genetic research due to their well-characterized genomes and ease of manipulation. While yeast is a unicellular organism that allows for rapid genetic studies, tomato plants are multicellular and exhibit more complex traits, including developmental and physiological responses to environmental changes. This difference influences experimental design and interpretation of results.

Phenotypic Analysis

Phenotypic analysis involves studying the observable characteristics of an organism resulting from the interaction of its genotype with the environment. In the context of high-salt acclimation, examining phenotypes of different alleles helps determine how specific genes affect the organism's ability to cope with stress. The approach to phenotypic analysis may vary between yeast and tomato plants due to differences in growth conditions, developmental stages, and the complexity of traits being studied.

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Textbook Question

Bacterial Pseudomonas species often possess plasmids encoding genes involved in the catabolism of organic compounds. You have discovered a strain that can metabolize crude oil and wish to identify the gene(s) responsible. Outline an experimental protocol to find the gene or genes required for crude oil metabolism.

Textbook Question

You have generated three transgenic lines of maize that are resistant to the European corn borer, a significant pest in many regions of the world. The transgenic lines (T₁ in the accompanying table) were created using Agrobacterium-mediated transformation with a T-DNA having two genes, the first being a gene conferring resistance to the corn borer and the second being a gene conferring resistance to a herbicide that you used as a selectable marker to obtain your transgenic plants. You crossed each of the lines to a wild-type maize plant and also generated a T₂ population by self-fertilization of the T₁ plant. The following segregation results were observed (herbicide resistant : herbicide sensitive):

Explain these segregation ratios.

Textbook Question

Two complaints about some transgenic plants presently in commercial use are that (1) the Bt toxin gene is constitutively expressed in them, leading to fears that selection pressures will cause insects to evolve resistance to the toxin, and (2) a selectable marker gene—for example, conferring kanamycin resistance—remains in the plant, leading to concerns about increased antibiotic resistance in organisms in the wild. How would you generate transgenic plants that produce Bt only in response to being fed upon by insects and without the selectable marker?

Textbook Question

You have isolated another cDNA clone of the CRABS CLAW gene from a cDNA library. The cDNA was directionally cloned using the EcoRI and XhoI sites. You sequence the recombinant plasmid using primers complementary to the T7 and T3 promoter sites flanking the MCS. The first 30 to 60 bases of sequence are usually discarded since they tend to contain errors.

Can you identify the start of the coding region in the end of the gene? What does the sequence preceding the start codon represent?

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Textbook Question

You have identified five genes in S. cerevisiae that are induced when the yeast are grown in a high-salt (NaCl) medium. To study the potential roles of these genes in acclimation to growth in high-salt conditions, you wish to examine the phenotypes of loss- and gain-of-function alleles of each. How will you do this?

Textbook Question

You have isolated another cDNA clone of the CRABS CLAW gene from a cDNA library.. The cDNA was directionally cloned using the EcoRI and XhoI sites. You sequence the recombinant plasmid using primers complementary to the T7 and T3 promoter sites flanking the MCS. The first 30 to 60 bases of sequence are usually discarded since they tend to contain errors.

Can you identify which sequence portions are derived from the vector (specifically the MCS) and which are derived from the cDNA clone?