Eukaryota, whose members are known as eukaryotes (/ - /,), is a diverse domain of organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea (both prokaryotes) make up the other two domains.
(Chatton, 1925) Whittaker & Margulis, 1978
|Supergroups and kingdoms|
The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard archaea. This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea. Eukaryotes represent a small minority of the number of organisms, but, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes. Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs. Their name comes from the Greek εὖ (eu, "well" or "good") and κάρυον (karyon, "nut" or "kernel").
Eukaryotic cells typically contain other membrane-bound organelles such as mitochondria and Golgi apparatus. Chloroplasts can be found in plants and algae. Prokaryotic cells may contain primitive organelles. Eukaryotes may be either unicellular or multicellular, and include many cell types forming different kinds of tissue. In comparison, prokaryotes are typically unicellular. Animals, plants, and fungi are the most familiar eukaryotes. Other eukaryotes are sometimes called protists.
Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four haploid daughter cells that act as sex cells or gametes. Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from genetic recombination during meiosis.