Question

I'm currently studying Plant Life Cycle (Alternation of Generations) and I don't understand why gametophytes produce sperm and eggs via mitosis and not meiosis, as mitosis is responsible for body cells and meiosis for sperm and eggs. Also, mitosis produces a diploid cell, then why are sperm and eggs haploid in this case?

Answer 1

the gametophyte is the structure that produces gametes, the gametophyte is haploid, and the sporophyte is diploid, 2 haploid gametes combine to form a zygote which develops into a diploid sporophyte, so gametes should be haploid. haploid gametophyte cannot undergo meiosis ( to undergo meiosis pair of homologous chromosomes are required, they pair up and exchange genetic material during prophase I ) so gametophyte undergo mitosis to produce haploid gamete, these haploid gametes combine to form zygote which develops into sporophyte (2n) which undergoes meiosis to produce spores which are haploid, this process gives genetic variability and haploid spores gives rise to haploid gametophyte.