Question 31 of 56
Q.Differentiate haplontic and diplontic life cycle.
Tamil Nadu DgeTamil Nadu HSC First Year (DGE) Board 2020Subjective· 3mImportance★★★★★
55% · 31/56 Questions
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Start your 14-day free trial to unlock the full solution →Haplontic and diplontic life cycles differ in which phase (haploid or diploid) is the dominant, multicellular one, and correspondingly in when meiosis occurs (immediately after zygote formation in haplontic vs at gamete formation in diplontic).
All sexually reproducing organisms alternate between a haploid (n) phase and a diploid (2n) phase, connected by fertilization (n + n -> 2n) and meiosis (2n -> n). Life cycles are classified by which phase is dominant (the larger, longer-lived, free-living multicellular phase):
Haplontic life cycle:
- The dominant, multicellular, free-living phase is HAPLOID (the gametophyte).
- The only diploid stage is the single-celled zygote, formed by fusion of two haploid gametes.
- The zygote undergoes meiosis IMMEDIATELY upon germination (called zygotic/initial meiosis) to regenerate the haploid phase — there is no multicellular diploid (sporophytic) generation.
- Example: Chlamydomonas, Volvox, and many green algae.
Diplontic life cycle:
- The dominant, multicellular, free-living phase is DIPLOID (the sporophyte).
- Meiosis occurs at the time of gamete formation itself (called gametic/terminal meiosis), directly producing haploid gametes.
- The haploid phase is represented only by the single-celled gametes — there is no multicellular gametophyte generation.
- Example: most animals (including humans), and among plants, some algae such as Fucus (a brown alga). …
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