USA Biology Olympiad (USABO) Practice Exam

Which generation in the life cycle of ferns is typically haploid?

1. Sporophyte

2. Gametophyte

3. Both Sporophyte and Gametophyte

4. Neither Generation

The correct answer is: Gametophyte

In the life cycle of ferns, the generation that is typically haploid is the gametophyte. Ferns exhibit a distinct alternation of generations, which involves two different phases: the sporophyte and the gametophyte. The sporophyte generation is the dominant and more recognizable phase, which is diploid. It develops from the fusion of gametes and produces spores through a process called meiosis. These spores are haploid and can grow into a gametophyte. In contrast, the gametophyte generation arises from these spores and is typically small, heart-shaped, and independent in many fern species. This stage is haploid, meaning it contains a single set of chromosomes. The gametophyte produces gametes (sperm and eggs) through mitosis, which are also haploid. When these gametes fuse during fertilization, they create a diploid zygote that then develops into a new sporophyte. Thus, the haploid stage of the fern life cycle is indeed the gametophyte generation, making it the correct answer.