Which generation is multicellular, haploid, and produces haploid gametes by mitosis?

Which generation is multicellular, haploid, and produces haploid gametes by mitosis?

• A. Sporophyte generation
• B. Gametophyte generation
• C. Zygotic generation
• D. Diploid generation

Answer: (B)

In alternation of generations, there are two multicellular stages with different ploidy. The haploid stage is the gametophyte: it comes from haploid spores and grows by mitosis, staying haploid. Because it’s haploid, every cell has one set of chromosomes, and this generation makes haploid gametes through mitosis. When two gametes unite, they form a diploid zygote that grows into the sporophyte, the other multicellular generation. The sporophyte is diploid and produces haploid spores by meiosis, which then develop into new gametophytes. The zygotic generation, in contrast, starts as a diploid zygote and immediately undergoes meiosis, not a multicellular haploid stage that produces gametes by mitosis. So the correct generation is the gametophyte generation.

In alternation of generations, there are two multicellular stages with different ploidy. The haploid stage is the gametophyte: it comes from haploid spores and grows by mitosis, staying haploid. Because it’s haploid, every cell has one set of chromosomes, and this generation makes haploid gametes through mitosis. When two gametes unite, they form a diploid zygote that grows into the sporophyte, the other multicellular generation. The sporophyte is diploid and produces haploid spores by meiosis, which then develop into new gametophytes. The zygotic generation, in contrast, starts as a diploid zygote and immediately undergoes meiosis, not a multicellular haploid stage that produces gametes by mitosis. So the correct generation is the gametophyte generation.