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Ch. 15 - Gene Mutation, DNA Repair, and Transposition
Chapter 15, Problem 4

Why would a mutation in a somatic cell of a multicellular organism not necessarily result in a detectable phenotype?

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1
Understand that somatic cells are any cells forming the body of an organism, excluding germ cells (sperm and egg).
Recognize that mutations in somatic cells are not passed on to offspring, as they do not affect the germ line.
Consider that a mutation in a single somatic cell may not affect the organism if the cell is not critical to the organism's function or if the mutation does not alter the cell's function significantly.
Realize that many somatic mutations are neutral, meaning they do not affect the cell's function or the organism's phenotype.
Acknowledge that the organism has many cells, and a mutation in one or a few cells may be masked by the normal function of the remaining healthy cells.

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Key Concepts

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

Somatic Cells

Somatic cells are any cells in a multicellular organism that are not germ cells (sperm or egg). They make up the majority of an organism's body and undergo mitosis for growth and repair. Mutations in somatic cells can occur without affecting the organism's overall phenotype, especially if they happen in non-coding regions of DNA or in cells that do not contribute to the organism's visible traits.
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Mutation Types

Mutations can be classified into several types, including silent, missense, and nonsense mutations. Silent mutations do not change the amino acid sequence of a protein, while missense mutations may alter a single amino acid, and nonsense mutations create a premature stop codon. A mutation in a somatic cell may not lead to a detectable phenotype if it is silent or occurs in a non-essential gene.
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Phenotype Expression

Phenotype refers to the observable characteristics of an organism, which result from the interaction of its genotype with the environment. Not all genetic changes lead to visible traits; some may be compensated for by other genes or may not affect the organism's function. Therefore, a mutation in a somatic cell may not manifest as a detectable phenotype if it does not influence the organism's overall appearance or health.
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Related Practice
Textbook Question

Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.

Which types of nucleotide changes (missense or synonyms) cause amino acid changes?

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Textbook Question

Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.

On what basis did the authors conclude that evidence of horizontal transfer is absent from their data?

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Textbook Question
What is a spontaneous mutation, and why are spontaneous mutations rare?
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Textbook Question

Most mutations are thought to be deleterious. Why, then, is it reasonable to state that mutations are essential to the evolutionary process?

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Textbook Question

Why is a random mutation more likely to be deleterious than beneficial?

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Textbook Question

Most mutations in a diploid organism are recessive. Why?

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