Editing G1 phase (section)

== Overview ==
[[File:Human karyotype with bands and sub-bands.png|thumb|250px|Schematic [[karyogram]] of the human chromosomes, showing their usual state in the G<sub>0</sub> and G<sub>1</sub> phase of the cell cycle. At top center it also shows the chromosome 3 pair in [[metaphase]] (annotated as "Meta."), which takes place after having undergone [[DNA synthesis]] which occurs in the [[S phase]] (annotated as S) of the cell cycle.<br>{{further|Karyotype}}]]
G<sub>1</sub> phase together with the [[S phase]] and [[G2 phase|G<sub>2</sub> phase]] comprise the long growth period of the [[cell cycle]] [[cell division]] called [[interphase]] that takes place before [[cell division]] in [[mitosis]] (M phase).<ref name=Lodish>{{cite book | first1 = Harvey | last1 = Lodish | first2 = Arnold | last2 = Berk | first3 = S Lawrence | last3 = Zipursky | first4 = Paul | last4 = Matsudaira | first5 = David | last5 = Baltimore | first6 = James | last6 = Darnell | name-list-style = vanc | title = Molecular cell biology | isbn = 978-0-7167-3136-8 | edition = 4th | url = https://archive.org/details/molecularcellbio00lodi | date = 2000 | location = New York | publisher = W. H. Freeman | url-access = registration }}</ref>

During G<sub>1</sub> phase, the cell grows in size and synthesizes [[mRNA]] and [[protein]] that are required for [[DNA]] synthesis. Once the required proteins and growth are complete, the cell enters the next phase of the cell cycle, S phase. The duration of each phase, including the G<sub>1</sub> phase, is different in many different types of cells. In human somatic cells, the  G<sub>1</sub> stage of the cell cycle lasts about 10 hours.<ref name=Morgan>{{cite book | last = Morgan | first = David | title = The Cell Cycle: Principals of Control | location = London | publisher = New Science Press LTD | date = 2007 }}</ref> However, in [[Xenopus]] embryos, [[sea urchin]] embryos, and [[Drosophila]] embryos, the G<sub>1</sub> phase is barely existent and is defined as the gap, if one exists, between the end of mitosis and the S phase.<ref name=Morgan />

G<sub>1</sub> phase and the other subphases of the cell cycle may be affected by limiting [[growth factors]] such as nutrient supply, temperature, and room for growth. Sufficient [[nucleotides]] and [[amino acids]] must be present in order to synthesize mRNA and proteins. Physiological temperatures are optimal for cell growth. In humans, the normal physiological temperature is around [[human body temperature|37 °C]] (98.6&nbsp;°F).<ref name= Lodish />

G<sub>1</sub> phase is particularly important in the cell cycle because it determines whether a cell commits to division or to leaving the cell cycle.<ref name= Morgan /> If a cell is signaled to remain undivided, instead of moving onto the S phase, it will leave the G<sub>1</sub> phase and move into a state of dormancy called the [[g0 phase|G<sub>0</sub> phase]]. Most nonproliferating vertebrate cells will enter the G<sub>0</sub> phase.<ref name= Lodish />