Ch. 16 - How Genes Work

Freeman - Biological Science 7th Edition

Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook

Freeman 7th Edition

Ch. 16 - How Genes Work

Problem 8

Chapter 16, Problem 8

Explain what's wrong with this statement: All point mutations change the genotype and the phenotype.

Verified step by step guidance

Understand the terms: A point mutation refers to a change in a single nucleotide base in the DNA sequence. The genotype is the genetic makeup of an organism, and the phenotype is the observable characteristics or traits of an organism.

Recognize the types of point mutations: There are different types of point mutations such as silent mutations, missense mutations, and nonsense mutations. Each type affects the genotype differently.

Consider silent mutations: Silent mutations are point mutations that do not change the amino acid sequence of the protein. Although they change the genotype (the DNA sequence), they do not alter the phenotype (the observable traits).

Analyze the impact of other mutations: Missense mutations change one amino acid in the protein, potentially altering the phenotype. Nonsense mutations introduce a stop codon prematurely, usually resulting in a nonfunctional protein, which changes the phenotype.

Conclude that the statement is incorrect: Not all point mutations change both the genotype and the phenotype. Silent mutations are an example where the genotype is altered but the phenotype remains unchanged.

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Key Concepts

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

Point Mutations

Point mutations are changes in a single nucleotide base pair in the DNA sequence. They can be classified into three types: silent, missense, and nonsense mutations. While some point mutations can lead to changes in the phenotype, others may not affect the phenotype at all, particularly silent mutations that do not alter the amino acid sequence of a protein.

Genotype vs. Phenotype

The genotype refers to the genetic makeup of an organism, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype and environmental influences. Not all changes in genotype lead to observable changes in phenotype, as some mutations may occur in non-coding regions or may not affect protein function.

Silent Mutations

Silent mutations are a specific type of point mutation that do not result in a change in the amino acid sequence of a protein. This occurs due to the redundancy in the genetic code, where multiple codons can code for the same amino acid. As a result, silent mutations can change the genotype without affecting the phenotype, contradicting the statement in question.

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Types of Mutations

Related Practice

Textbook Question

Which of the following describes mutations? Select True or False for each statement.T/F Point mutations can occur in any DNA sequence.T/F Frameshift mutations can occur in any DNA sequence.T/F Neutral mutations depend on the degeneracy of the genetic code.T/F Deleterious mutations occur only in protein-coding sequences of DNA.

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Textbook Question

In a particular bacterial species, temperature-sensitive conditional mutations cause expression of a wild-type phenotype at one growth temperature and a mutant phenotype at another—typically higher—temperature. Imagine that when a bacterial cell carrying such a mutation is shifted from low to high growth temperatures, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects:a. the terminator sequenceb. the start codonc. sigmad. one of the polypeptides of the core RNA polymerase

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Textbook Question

Explain what's wrong with this statement: All point mutations change the genotype and the phenotype.

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Textbook Question

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.) (a) Suppose a mutation made the gene for enzyme C nonfunctional. What molecule would accumulate in the affected cells?

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Textbook Question

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.) (b) Suppose a mutant strain can survive if substrate 5 is added to the growth medium, but it cannot grow if substrates 1, 2, 3, or 4 are added. Which enzyme in the pathway is affected in this mutant?

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Textbook Question

Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.)

(a) Suppose a mutation made the gene for enzyme C nonfunctional. What molecule would accumulate in the affected cells?

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