Massachusetts Comprehensive Assessment System (MCAS) Biology Practice Test

What aspect of an organism's phenotype can mutations directly affect?

1. Environmental factors surrounding the organism.

2. Nucleic acid sequence

3. Amino acid synthesis pathways.

4. Protein folding mechanisms.

The correct answer is: Nucleic acid sequence

Mutations are changes in the nucleotide sequence of an organism’s DNA, which can directly influence the organism's phenotype. A phenotype refers to the observable physical or biochemical characteristics of an organism, which arise from the expression of genes and the interaction of these genes with the environment. When a mutation occurs in the nucleic acid sequence, it can alter the way that genetic information is translated into proteins. These proteins play crucial roles in determining an organism’s traits. For example, a mutation may lead to a different amino acid being incorporated into a protein, potentially changing its structure and function, and, consequently, the organism's phenotype. Examining the other options reveals that while they may be related to biological processes, they do not directly pertain to the immediate effects of mutations on phenotype. Environmental factors can influence phenotype but are not a consequence of mutations. Amino acid synthesis pathways may be impacted by mutations if they affect the genes associated with these pathways, but the synthesis pathways themselves are not directly altered by a mutation. Similarly, while mutations can affect protein folding mechanisms by changing the protein's primary structure, the direct effect of a mutation is on the nucleic acid sequence itself. Therefore, nucleic acid sequence is the most direct aspect related to mutations and their effects