Advanced Placement (AP) Biology Practice Exam

Where are extranuclear genes located?

1. In the nucleus of the cell

2. In the cytoplasm of organelles

3. In the cell membrane

4. In the ribosomes

The correct answer is: In the cytoplasm of organelles

Extranuclear genes are located in the cytoplasm of organelles, specifically within mitochondria and chloroplasts. These organelles contain their own DNA, which is distinct from the nuclear DNA found in the cell's nucleus. This extranuclear DNA is involved in encoding proteins that are essential for the functions of the organelles, such as energy production in mitochondria and photosynthesis in chloroplasts. The presence of this genetic material supports the endosymbiotic theory, which suggests that these organelles originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Thus, the correct answer highlights the unique genetic contributions of organelles outside the nucleus to cellular function.