Question

In plant cells meiosis cannot occur in haploid cell

Answer 1

Most fungi and some protists (unicellular eukaryotes) have a haploid-dominant life cycle, in which the “body” of the organism—that is, the mature, ecologically important form—is haploid.

An example of a fungus with a haploid-dominant life cycle is black bread mold, whose sexual life cycle is shown in the diagram below. In sexual reproduction of this mold, hyphae (multicellular, thread-like haploid structures) from two compatible individuals first grow towards each other.

Where the hyphae meet, they form a structure called the zygosporangium. A zygosporangium contains multiple haploid nuclei from the two parents within a single cell. The haploid nuclei fuse to form diploid nuclei, which are equivalent to zygotes. The cell containing the nuclei is called the zygospore.

Example of a haploid-dominant life cycle: black bread mold. A haploid spore (1n) undergoes mitosis to produce a multicellular individual (1n) with thread-like structures called hyphae. Two hyphae of compatible (+ and -) mating types extend protrusions towards one another, and where the protrusions meet, they form a zygosporangium with multiple haploid nuclei inside (some from both parent hyphae). Nuclear fusion then takes place, in which the haploid nuclei fuse to form diploid nuclei, and the cell containing the diploid nuclei is called the zygospore. The diploid nuclei in the zygospore undergo meiosis to produce haploid nuclei, which are released as unicellular spores (1n), and the cycle repeats.

The zygospore may stay dormant for long periods of time, but under the right conditions, the diploid nuclei undergo meiosis to make haploid nuclei that are released in single cells called spores^44start superscript, 4, end superscript. Because they were formed through meiosis, each spore has a unique combination of genetic material. The spores germinate and divide by mitosis to make new, multicellular haploid fungi