Bikont
Eukaryotes defined by a fused TS-DHFR gene, including plants and many protists.
Zygmunt Put · CC BY-SA 4.0
Bikonts are a major group of eukaryotic organisms primarily defined by a fused TS-DHFR gene, not by the presence of two flagella. This group includes many single-celled and multi-celled organisms, and while many bikonts have two flagella, the defining molecular trait is the fusion of the genes for thymidylate synthase and dihydrofolate reductase into a single unit. Bikonts are significant in evolutionary biology as one of the two primary divisions of eukaryotes, the other being unikonts.
- definition
- Eukaryotic organisms defined by a fused TS-DHFR gene
- key_trait
- Fusion of thymidylate synthase and dihydrofolate reductase genes into a single unit
- includes
- Archaeplastida, Excavata, Rhizaria, Chromalveolata, and possibly Apusozoa
- alternative_name
- Diphoda (proposed in 2015)
- contrasting_group
- Unikonts (separate TS and DHFR genes)
Quick Facts
- Taxon
- Bikonta
- Subdivision
- Diaphoretickes / Excavata / Hemimastigophora
Facts from the source article.
Lore & Background
Bikonts are primarily defined by the fusion of the genes for thymidylate synthase and dihydrofolate reductase into a single gene that encodes a bifunctional protein; in unikonts, these genes are translated separately. A shared molecular trait is this gene fusion, not the presence of two flagella. Bikonts are the clade that includes Archaeplastida (plants and relatives), Excavata, Rhizaria, and Chromalveolata, rather than a single ancestral organism giving rise to these groups.
Reader's Guide
The bikont group represents a fundamental split in the eukaryotic tree of life, contrasting with unikonts (which include animals, fungi, and Amoebozoa). Relationships within bikonts remain unresolved, with competing hypotheses: Cavalier-Smith grouped Excavata and Rhizaria into Cabozoa, and Archaeplastida and Chromalveolata into Corticata, while other studies suggest Rhizaria and Chromalveolata form a clade. An alternative nomenclature proposed in 2015 uses 'Diphoda' for bikonts. The corticates roughly correspond to bikonts. While many subgroups like Haptophyta, Cryptophyta, and Viridiplantae are considered monophyletic, Archaeplastida may be paraphyletic. Recent reconstructions placed Archaeplastida and Hacrobia together in an HA supergroup, but this has fallen out of favor due to disputes over hacrobian monophyly. The group's significance lies in its role in understanding early eukaryotic evolution and the diversification of major lineages.
Did You Know?
- Bikonts have a fused gene for thymidylate synthase and dihydrofolate reductase, while unikonts have separate genes.
- Cavalier-Smith suggested that Apusozoa, typically considered incertae sedis, are actually bikonts.
- An alternative name for bikonts is Diphoda, proposed in 2015.
- In Cavalier-Smith's system, corticates are a subgroup within bikonts, not roughly equivalent to bikonts as a whole.
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Frequently Asked Questions
What is a bikont?
Bikonts make up one of the two major branches of eukaryotic life, encompassing an enormous range of organisms from simple single-celled protists to complex multicellular forms like all plants. They stand as the counterpart to the other primary eukaryotic lineage, the unikonts, and together these two groups account for essentially all known eukaryotes.
Are bikonts defined by having two flagella?
Although the name hints at a two-flagellum structure and many members do bear two, the true defining trait is molecular: the thymidylate synthase and dihydrofolate reductase genes are fused into a single combined unit. This genetic signature is what actually unites the group, making flagellar number a secondary and sometimes variable feature rather than the core criterion.
Which major lineages are included in the bikont group?
The bikont clade traditionally encompasses Archaeplastida (the lineage containing all plants), Excavata, Rhizaria, and Chromalveolata, with Apusozoa sometimes added as well. This makes it an extraordinarily diverse assemblage stretching from familiar trees and flowers to obscure marine protists.
How do bikonts differ from unikonts?
The fundamental split in eukaryotic evolution divides organisms into these two camps, with unikonts characterized by a single flagellum and the absence of the fused TS-DHFR gene arrangement. In practical terms, animals, fungi, and amoebozoans belong to the unikont side, while plants, most algae, and a wide array of other protists fall on the bikont side.
What is 'Diphoda' and how does it relate to bikonts?
Diphoda is an alternative name proposed in 2015 for what is more commonly called the bikont group, referring to the same collection of eukaryotic organisms. The term emphasizes the historical two-flagellum characterization, though as with 'bikont,' the genuine unifying feature remains the fused TS-DHFR gene rather than flagellar count alone.
More in Higher-Level Taxonomy & Evolution 1-24
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