Question

A haploid parent produces gametes by mitotic division. Does this mean that meiosis never occurs in organisms that are haploid?

Answer 1

Mitosis is a process which leads to formation of two identical daughter cells from a single parent cell. It is used for cell growth and replacement of worn out cells. It is called equational division. Meiosis is a phenomenon in cell division, which reduces the number of chromosomes in parent cells by half. It produces gamete cells, which are four in number. It is essential for production of egg and sperm cells for the process of sexual production.

Complete answer:
Meiosis can’t occur in haploid cells. Haploid parent (n) is able to produce gametes (n) via mitosis. The male gamete (n) and female gamete (n) are fused by the process of fertilization, which produces a zygote. Zygote is diploid ($2n$). Then, the zygote, which is a diploid cell, undergoes meiosis to produce a haploid one (n) again. Haploid organisms (algae like Spirogyra , Volvox) have meiosis stage in zygotic stage. Their haploid gamete cells fuse together and produce diploid zygote, when then undergoes meiotic process to produce haploid spores. These spores undergo mitosis to produce gametophyte. Formation of the zygote cell is the only diploid phase in these organisms. Haploid parents produce gametes by mitotic division to maintain the equal number of chromosomes in cells. Hence, meiosis can’t occur in haploid organisms. Meiosis can occur only in diploid organisms or in the diploid stage of their life cycle.

Note:
Generally, diploid stage is called sporophyte and haploid stage is called gametophyte. Meiotic process happens in sporophyte to produce spores and mitotic process occurs in gametophyte for the production of gametes. Mitosis is the longer cell cycle and it delivers gametes. Mitosis increases the ploidy level, while meiosis decreases the same. To maintain the chromosome number in the gametes, mitotic division occurs in the haploid parent.