Question

Sometimes a segment of DNA breaks off from a chromosome, then returns to the correct place on the original chromosome, but in reverse order. This type of chromosomal structural change is called a. crossing-over b. a translocation. c. an inversion. d. a deletion.

Short answer

c. an inversion.

Step-by-step solution

Understand the DNA Segments

A DNA segment can sometimes break off from a chromosome, which means it separates from the main structure of the DNA molecule.

Identify the Return to Original Chromosome

After breaking off, the segment returns to the original chromosome.

Recognize the Reversed Order

When the segment returns, it is not in its original order. Instead, it is reversed.

Review Chromosomal Structural Changes

Crossing-over refers to the exchange of segments between homologous chromosomes. A translocation involves a segment moving to a different chromosome. Deletion is the loss of a chromosome segment. An inversion is when a segment returns in the reverse order.

Determine the Correct Answer

Given that the segment returns in reverse order, it is indicative of an inversion.

Key concepts

DNA structural changes

DNA structural changes are modifications in the arrangement and organization of DNA within the chromosomes. These changes can occur due to different reasons, such as environmental factors, errors during cell division, or exposure to mutagens. Common types of DNA structural changes include:

• Crossing-over: The exchange of DNA segments between homologous chromosomes during meiosis.
• Translocation: A segment of a chromosome moves to a different chromosome.
• Deletion: The loss of a portion of a chromosome.
• Inversion: A segment breaks off and reattaches to the original chromosome in reverse order.

These changes can have various effects on an organism, from benign to causing serious genetic disorders.

Chromosome segments

Chromosome segments are parts of the chromosomes that house genes and regulatory elements controlling various biological functions. Each segment has a specific sequence of DNA that codes for certain traits or characteristics.
When a segment undergoes changes, it can impact the genetic instructions within the segment, leading to different outcomes. For example:

• Segments can break and reattach: Such as during an inversion where the segment reattaches in reverse order.
• Genes may be disrupted: If the break occurs within a gene, it can disrupt its function.
• Regulatory elements might change: This can lead to changes in gene expression, even if the actual gene sequence is unaffected.

These types of chromosomal modifications illustrate the importance of maintaining the structural integrity of chromosome segments for genetic stability.

Genetic mutations

Genetic mutations refer to changes in the DNA sequence that make up a gene. These mutations can be caused by errors during DNA replication, environmental factors like UV radiation, or exposure to chemical agents.
Mutations can be classified in several ways, including:

• Point mutations: A single nucleotide change in the DNA sequence.
• Insertions and deletions: Additions or removals of small DNA segments.
• Inversions: Entire segments of DNA are reversed in orientation.
• Translocations: Segments of DNA move to different chromosomes.

The effects of mutations vary widely. Some mutations are harmless, while others can lead to diseases, developmental problems, or beneficial adaptive traits.
Understanding the various types of genetic mutations helps in studying how genetic diversity and disease susceptibility occur.