Ch. 15 - Gene Mutation, DNA Repair, and Transposition

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of GeneticsISBN: 9780135564776당신이 사용하는 게 아니라요?교과서 변경

Klug 12th Edition

Ch. 15 - Gene Mutation, DNA Repair, and Transposition

문제 21

15장, 문제 21

In maize, a Ds or Ac transposon can alter the function of genes at or near the site of transposon insertion. It is possible for these elements to transpose away from their original insertion site, causing a reversion of the mutant phenotype. In some cases, however, even more severe phenotypes appear, due to events at or near the mutant allele. What might be happening to the transposon or the nearby gene to create more severe mutations?

검증된 단계별 안내

Understand that transposons like Ds (Dissociation) and Ac (Activator) can move within the genome, which can disrupt gene function when they insert into or near genes.

Recognize that when a transposon excises (moves out) from its original site, it can sometimes restore the gene's function, leading to a reversion of the mutant phenotype.

Consider that during the excision process, the transposon may not leave the DNA cleanly; it can cause small insertions or deletions (indels) at the excision site, which can further disrupt the gene.

Realize that these imprecise excision events can create more severe mutations if they alter the coding sequence or regulatory regions of the gene, potentially causing frameshifts or loss of important gene elements.

Also, transposon movement can cause chromosomal rearrangements or affect nearby genes, which might contribute to the appearance of more severe phenotypes.

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Transposons and Their Mechanism of Transposition

Transposons, such as Ds and Ac elements in maize, are DNA sequences that can move within the genome. They insert into genes or regulatory regions, disrupting normal gene function. Their movement can be cut-and-paste or replicative, causing mutations or reversions depending on insertion or excision events.

Effects of Transposon Excision and Footprint Mutations

When a transposon excises from a gene, it may leave behind small insertions or deletions called footprints. These residual changes can alter the gene's coding sequence or regulatory elements, sometimes causing more severe mutations than the original insertion by disrupting gene function more extensively.

Local Genomic Instability Induced by Transposons

Transposon activity can induce genomic instability near the insertion site, including chromosomal rearrangements, duplications, or deletions. Such events can exacerbate mutant phenotypes by affecting multiple genes or regulatory regions, leading to more severe or novel mutations beyond simple insertional disruption.

관련 실천

교과서 질문

Compare DNA transposons and retrotransposons. What properties do they share?

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교과서 질문

It is estimated that about 0.2 percent of human mutations are due to TE insertions, and a much higher degree of mutational damage is known to occur in some other organisms. In what way might a TE insertion contribute positively to evolution?

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교과서 질문

Presented here are hypothetical findings from studies of heterokaryons formed from seven human xeroderma pigmentosum cell strains:

These data are measurements of the occurrence or nonoccurrence of unscheduled DNA synthesis in the fused heterokaryon. None of the strains alone shows any unscheduled DNA synthesis. Which strains fall into the same complementation groups? How many different groups are revealed based on these data? What can we conclude about the genetic basis of XP from these data?

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교과서 질문

Speculate on how improved living conditions and medical care in the developed nations might affect human mutation rates, both neutral and deleterious.

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교과서 질문

In a bacterial culture in which all cells are unable to synthesize leucine (leu⁻), a potent mutagen is added, and the cells are allowed to undergo one round of replication. At that point, samples are taken, a series of dilutions are made, and the cells are plated on either minimal medium or minimal medium containing leucine. The first culture condition (minimal medium) allows the growth of only leu⁺ cells, while the second culture condition (minimal medium with leucine added) allows growth of all cells. The results of the experiment are as follows:

What is the rate of mutation at the locus associated with leucine biosynthesis?

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교과서 질문

What genetic defects result in the disorder xeroderma pigmentosum (XP) in humans? How do these defects create the phenotypes associated with the disorder?

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