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Self-replication is a fundamental feature of life. It was proposed that self-replication emerged in the evolution of life when a molecule similar to a double-stranded polynucleotide (possibly like RNA) dissociated into single-stranded polynucleotides and each of these acted as a template for synthesis of a complementary strand producing two double stranded copies. [4]
In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself.
Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote, which itself is produced by fusion of two gametes, each having been produced by meiotic cell division. [5] [6] After growth from the zygote to the adult, cell division by mitosis allows for continual construction and repair of the organism. [7]
The Neuronal cell cycle represents the life cycle of the biological cell, its creation, reproduction and eventual death. The process by which cells divide into two daughter cells is called mitosis . Once these cells are formed they enter G1, the phase in which many of the proteins needed to replicate DNA are made.
Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids. [citation needed]
Three basic categories of cells make up the mammalian body: germ cells, somatic cells, and stem cells.Each of the approximately 37.2 trillion (3.72x10 13) cells in an adult human has its own copy or copies of the genome except certain cell types, such as red blood cells, that lack nuclei in their fully differentiated state.
Viruses can reproduce only inside cells, and they can gain entry by using many of the receptors involved in immunity. Once inside the cell, viruses use the cell's biological machinery to their own advantage, forcing the cell to make hundreds of identical copies of themselves.
This continual division of labile cells allows them to reproduce new stem cells and replace functional cells that are lost in the body. [1] Functional cells may be lost through necrosis , which is the premature death of cells caused by environmental disturbances, such as diseases or injuries. [ 3 ]