Ch. 16 - How Genes Work

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 16 - How Genes Work

Problem 11

Chapter 16, Problem 11

Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele?
a. A missense mutation
b. A frameshift mutation
c. A neutral mutation
d. A silent mutation

Verified step by step guidance

Understand the concept of a null allele: A null allele is a version of a gene that completely lacks normal function. This can occur due to mutations that disrupt the gene's ability to produce a functional protein.

Analyze the types of mutations provided: a missense mutation changes one amino acid in the protein, a frameshift mutation alters the reading frame of the gene, a neutral mutation has no effect on protein function, and a silent mutation does not change the amino acid sequence of the protein.

Determine which mutation is most likely to create a null allele: A frameshift mutation is most likely to create a null allele because it can drastically alter the protein's structure by shifting the reading frame, leading to a completely nonfunctional protein or premature stop codons.

Eliminate other options: A missense mutation might only partially affect protein function, a neutral mutation has no effect on function, and a silent mutation does not change the protein at all. These are less likely to result in a null allele.

Conclude that the most likely mutation to create a null allele in this case is a frameshift mutation, as it has the potential to completely disrupt the protein's function.

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Key Concepts

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

Types of Mutations

Mutations are changes in the DNA sequence that can affect gene function. The main types include missense mutations, which change one amino acid in a protein; frameshift mutations, which alter the reading frame of the gene; silent mutations, which do not change the amino acid sequence; and neutral mutations, which have no effect on fitness. Understanding these types is crucial for determining how they impact protein function and phenotypic traits.

Null Alleles

A null allele is a variant of a gene that results in a complete loss of function of the gene product, often due to mutations that disrupt protein synthesis. This can occur through various mechanisms, such as frameshift mutations or premature stop codons. Identifying mutations that create null alleles is important for understanding genetic diseases and traits, such as skin pigmentation in this context.

Frameshift Mutation

A frameshift mutation occurs when nucleotides are inserted or deleted from the DNA sequence, causing a shift in the reading frame during translation. This often results in a completely different and nonfunctional protein due to altered amino acid sequences and can lead to the creation of a null allele. Frameshift mutations are particularly significant in understanding genetic disorders and phenotypic variations.

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Types of Mutations

Related Practice

Textbook Question

A small portion of the human transport protein amino acid sequence is shown here. The upper sequence is associated with darker skin, and the lower sequence is associated with lighter skin. What DNA base-pair change created the light-skin form of the human protein from the gene that coded for the dark-skin form?

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

Investigators examined the expression of transporter mRNA and protein produced in zebrafish homozygous for each of the alleles and obtained the results summarized here (+=present,−=absent). Does the allele associated with light color appear to be altering transcription ortranslation? Why?

Textbook Question

Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

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Textbook Question

One of the possibilities considered about the genetic code was that the code was overlapping, meaning that a single base could be part of up to three codons. How many amino acids would be encoded in the sequence 5′-AUGUUACGGAAU-3′ by a non-overlapping and a maximally overlapping triplet code?

a. 4 (non-overlapping) and 16 (overlapping)

b. 4 and 12

c. 4 and 10

d. 12 and 4

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Textbook Question

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

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