Zygotic meiosis is meiosis of a zygote immediately after karyogamy which is the fusion of two cell nuclei. This way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form either larger, multicellular individuals or more haploid cells.
Zygotic meiosis takes place in some lower plants and animals. They don’t form haploid gametes, in them the male and the female sex cells are diploid and they fuse to form tetraploid zygote on fertilization. This zygote in turn undergoes meiosis to get normal diploid set of chromosomes.
What You Need To Know About Zygotic Meiosis
- Zygote is the only diploid structure in the life cycle.
- The dominant individual in the life cycle is haploid hence the life cycle is haplontic.
- Meiosis takes place at the time of zygote germination
- This life cycle appears in all fungi, many protozoa and some algae.
In gametic meiosis, instead of immediately dividing meiotically to produce haploid cells, the zygote divides mitotically to produce a multicellular diploid individual or a group of more unicellular diploid cells. Cells from the diploid individuals then undergo meiosis to produce haploid cells or gametes.
Haploid cells may divide to form more haploid cells, as in many yeasts but the haploid phase is not the predominant life cycle phase. In most diplonts, mitosis occurs only in the diploid phase i.e gametes usually form quickly and fuse to produce diploid zygotes.
The diploid multicellular individual is a diplont hence a gametic meiosis is also referred to as diplontic life cycle. Diplonts are:
- Some brown algae
- Some fungi e.g brewer’s yeast.
What You Need To Know About Gametic Meiosis
- All structures except gametes are diploid.
- The dominant individual in the life cycle is diploid.
- Meiosis occurs only at the time of gamete formation.
- Some brown and green algae, animals and many other organisms maintain this type of life cycle.
In sporic meiosis, the zygote divides mitotically to produce a multicellular diploid ‘’sporophyte’’. The sporophyte creates spores via meiosis which also then divides mitotically producing haploid individuals referred to as ‘’gametophytes’’. Gametophytes now produce gametes via mitosis. In many plants, the gametophyte is not only small-sized but also short-lived.
In the whole cycle, gametes are usually the only haploid cells and mitosis usually occurs only in the diploid phase. Haplodiplonts include:
- Most plants
- Some fungi
What You Need To Know About Sporic Meiosis
- In sporic meiosis (also commonly referred to as intermediary meiosis), the zygote divides mitotically to produce a multicellular diploid sporophyte.
- Meiotic division occurs during sporogenesis
- Results in formation of haploid spores.
- Spore divides to form gametophytes which will form gametes. Gametes fusion results in diploid sporophyte i.e having Diplohaplontic life cycle.
- This life cycle is common in angiosperms.
Difference Between Zygotic, Gametic And Sporic Meiosis In Tabular Form
|BASIS OF COMPARISON||ZTGOTIC MEIOSIS||GAMETIC MEIOSIS||SPORIC MEIOSIS|
|Description||Zygote is the only diploid structure in the life cycle.||All structures except gametes are diploid.||In sporic meiosis (also commonly referred to as intermediary meiosis), the zygote divides mitotically to produce a multicellular diploid sporophyte.|
|Occurrence||Meiosis takes place at the time of zygote germination||Meiosis occurs only at the time of gamete formation.||Meiotic division occurs during sporogenesis|
|Results||The dominant individual in the life cycle is haploid hence the life cycle is haplontic.||The dominant individual in the life cycle is diploid.||Results in formation of haploid spores.|
|Presence||This life cycle appears in all fungi and some algae.||Some brown and green algae, animals and many other organisms maintain this type of life cycle.||This life cycle is common in angiosperms.|