Living Environment Regents Practice Test

During chromosome replication, which event occurs first when a genetic error happens?

1. New proteins are produced

2. New mRNA is synthesized

3. A DNA strand with an altered sequence is formed

4. A new inheritable trait is expressed

The correct answer is: A DNA strand with an altered sequence is formed

During chromosome replication, if a genetic error occurs, the formation of a DNA strand with an altered sequence is the first event that takes place. This step is fundamental because errors can arise during the actual replication of DNA. A mutation or change in the nucleotide sequence can occur, leading to a DNA strand that differs from the original template. This altered sequence results from mispairing of nucleotides or issues during the DNA synthesis process. Once altered DNA is created, subsequent processes such as transcription and translation can happen, leading to the production of new mRNA and potential new proteins. These changes can then contribute to the expression of new traits, but they follow after the initial alteration in the DNA sequence itself. Hence, the immediate outcome of the genetic error is the formation of this modified DNA strand, making it the first event in the sequence of consequences stemming from the error.