Animals, plants, fungi, and protists are eukaryotes. Eukaryotes are organisms whose cells are organized into complex structures enclosed within membranes. The defining membrane-bound structure which differentiates eukaryotic cells from prokaryotic - Bacteria and Archaea - cells is the nucleus. The presence of a nucleus gives these organisms their name, which comes from the Greek ευ, meaning “good/true”, and κάρυον, “nut”. Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies.
Cell division in eukaryotes is different from organisms without a nucleus (prokaryotes). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically-identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.- wikipedia
Phylogenetic tree showing extensive horizontal gene transfer between domains and an ancestral colony as the root of the tree.
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