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Ch. 4 - Gene Interaction
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 4 - Gene InteractionProblem 4a
Chapter 4, Problem 4a

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.
Using terminology, characterize the 12 colonies that grow on minimal medium and the 3 colonies that do not.

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1
Identify the type of medium used: A complete medium contains all the nutrients required for bacterial growth, while a minimal medium contains only the essential nutrients that the bacteria must synthesize themselves.
Characterize the 12 colonies that grow on minimal medium: These colonies are considered prototrophs, meaning they can synthesize all the compounds they need for growth from the minimal medium's basic nutrients.
Characterize the 3 colonies that do not grow on minimal medium: These colonies are considered auxotrophs, meaning they have mutations that prevent them from synthesizing one or more essential compounds, which must be provided externally for their growth.
Explain the genetic basis: The auxotrophic colonies likely have mutations in genes responsible for the biosynthesis of specific nutrients, such as amino acids, nucleotides, or vitamins, which are absent in the minimal medium.
Summarize the distinction: Prototrophs are wild-type bacteria capable of growing on minimal medium, while auxotrophs are mutants that require supplementation of specific nutrients to grow.

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Key Concepts

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

Complete Medium vs. Minimal Medium

Complete medium contains all the nutrients necessary for bacterial growth, including amino acids, vitamins, and other growth factors. In contrast, minimal medium provides only the essential nutrients required for growth, typically a carbon source, nitrogen, salts, and water. Understanding the difference between these media is crucial for characterizing bacterial colonies based on their nutritional requirements.
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Auxotrophs and Prototrophs

Prototrophs are bacteria that can synthesize all the compounds they need for growth from minimal medium, while auxotrophs lack the ability to synthesize one or more essential compounds and require additional nutrients found in complete medium. In this context, the 12 colonies that grow on minimal medium are likely prototrophs, whereas the 3 colonies that do not grow are auxotrophs, indicating their specific nutrient deficiencies.
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Selection Pressure

Selection pressure refers to environmental factors that favor certain traits over others, influencing the survival and reproduction of organisms. In this scenario, transferring colonies from complete to minimal medium creates a selection pressure that favors prototrophic bacteria capable of surviving on limited nutrients, while auxotrophic colonies are unable to thrive, highlighting the importance of nutrient availability in microbial growth.
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Related Practice
Textbook Question

Define and distinguish incomplete penetrance and variable expressivity.

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Define and distinguish epistasis and pleiotropy.

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Textbook Question

When working on barley plants, two researchers independently identify a short-plant mutation and develop homozygous recessive lines of short plants. Careful measurements of the height of mutant short plants versus normal tall plants indicate that the two mutant lines have the same height. How would you determine if these two mutant lines carry mutation of the same gene or of different genes?

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Textbook Question

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

The three colonies that do not grow on minimal medium are transferred to minimal medium supplemented with the amino acid serine (min + Ser), and all three colonies grow. Characterize these three colonies.

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Textbook Question

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

The serine biosynthetic pathway is a three-step pathway in which each step is catalyzed by the enzyme product of a different gene, identified as enzymes A, B, and C in the diagram below.


Mutant 1 grows only on min + Ser. In addition to growth on min + Ser, mutant 2 also grows on min + 3-PHP and min + 3-PS. Mutant 3 grows on min + 3-PS and min + Ser. Identify the step of the serine biosynthesis pathway at which each mutant is defective.

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Textbook Question

In a type of parakeet known as a "budgie," feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino).

a. List the genotypes for green, yellow, blue, and albino budgies

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