Textbook Question
How would the results vary in cross (a) of Problem 32 if genes A and B were linked with no crossing over between them? How would the results of cross (a) vary if genes A and B were linked and 20 map units (mu) apart?
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Ch. 13 - Translation and Proteins
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 13, Problem 22
A series of mutations in the bacterium Salmonella typhimurium results in the requirement of either tryptophan or some related molecule in order for growth to occur. From the data shown here, suggest a biosynthetic pathway for tryptophan.
Verified step by step guidance1
Step 1: Analyze the growth pattern of each mutant on different supplements. Note which mutants grow (+) or do not grow (−) on minimal medium, anthranilic acid, indole glycerol phosphate, indole, and tryptophan.
Step 2: Identify the position of each mutation in the biosynthetic pathway by determining the earliest supplement that restores growth. For example, if a mutant grows when anthranilic acid is added but not on minimal medium, the mutation likely affects a step before anthranilic acid synthesis.
Step 3: Arrange the compounds in order based on the mutants' growth patterns. Since trp-8 grows with anthranilic acid, indole glycerol phosphate, indole, and tryptophan, but not on minimal medium, anthranilic acid must be upstream of the mutation in trp-8.
Step 4: Use the pattern of growth restoration to infer the sequence of intermediates in the tryptophan biosynthesis pathway. For example, if trp-3 grows only when indole, indole glycerol phosphate, or tryptophan is added, but not with anthranilic acid, then indole glycerol phosphate is downstream of the mutation in trp-3.
Step 5: Summarize the biosynthetic pathway by ordering the intermediates from anthranilic acid to indole glycerol phosphate to indole to tryptophan, placing the mutations accordingly to reflect the block in the pathway.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Biosynthetic Pathways
Biosynthetic pathways are sequences of enzymatic reactions that convert simple molecules into complex products, such as amino acids. Understanding these pathways helps identify the order of intermediate compounds and the enzymes involved. Mutations blocking specific steps cause accumulation or requirement of intermediates, revealing pathway structure.
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Guided course
05:44
Repair Pathways
Genetic Mutations and Auxotrophy
Mutations in genes encoding enzymes of a biosynthetic pathway can cause auxotrophy, where an organism requires an external supply of a nutrient it normally synthesizes. By analyzing which supplements restore growth in mutants, one can infer the position of the mutation in the pathway and the intermediates involved.
Recommended video:
Guided course
10:48Mutations and Phenotypes
Use of Growth Supplementation Tests
Growth supplementation tests involve providing mutants with various pathway intermediates to determine which compounds rescue growth. This method helps map the biosynthetic pathway by identifying the earliest compound that restores growth, indicating the step at which the mutation blocks synthesis.
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Guided course
09:46Mitosis Steps
Related Practice
Textbook Question
Many antibiotics are effective as drugs to fight off bacterial infections because they inhibit protein synthesis in bacterial cells. Using the information provided in the following table that highlights several antibiotics and their mode of action, discuss which phase of translation is inhibited: initiation, elongation, or termination. What other components of the translational machinery could be targeted to inhibit bacterial protein synthesis?
Textbook Question
Three independently assorting genes (A, B, and C) are known to control the following biochemical pathway that provides the basis for flower color in a hypothetical plant:
Three homozygous recessive mutations are also known, each of which interrupts a different one of these steps. Determine the phenotypic results in the F1 and F2 generations resulting from the P1 crosses of true-breeding plants listed here:
colorless (aaBBCC) × green (AABBcc)
Textbook Question
Three independently assorting genes (A, B, and C) are known to control the following biochemical pathway that provides the basis for flower color in a hypothetical plant:
Three homozygous recessive mutations are also known, each of which interrupts a different one of these steps. Determine the phenotypic results in the F1 and F2 generations resulting from the P1 crosses of true-breeding plants listed here:
yellow (AAbbCC) × green (AABBcc)