Fungi have life cycles that are predominantly in which ploidy stage?

• A. Diploid
• B. Haploid
• C. Triploid
• D. Polyploid

Answer: (B)

Fungi spend most of their life as haploid. Their vegetative forms—hyphae and, in yeasts, the growing cells—carry a single set of chromosomes. Sexual reproduction brings two haploid nuclei together to form a diploid zygote, but that diploid stage is brief; it quickly undergoes meiosis to produce haploid spores, which restart the cycle. Some fungi show a long-lasting dikaryotic stage, where two distinct haploid nuclei share the same cell, but this is not a true diploid state. Because the organism’s cells are typically haploid for the majority of the life cycle, haploid is the best description.