細胞分裂是一個重要的生物學過程，它使細胞能夠成長、修復受損細胞、取代死亡細胞，並進行繁殖。而細胞分裂分為兩種形式：有絲分裂和減數分裂。
有絲分裂會從一個”母細胞”分裂出兩個遺傳上相同的”子細胞”，而減數分裂則產生與母細胞遺傳不同且僅含有一半DNA量的細胞。大部分身體細胞都會進行有絲分裂，但某些細胞相對於其他細胞會更頻繁地進行有絲分裂。例如，位於胃壁的細胞每隔幾天就會自我替換，因為它們需要抵抗強烈的消化酸。相比之下，肝細胞可能需要長達一年的時間才會進行自我替換。還有一些細胞，例如某些神經細胞和眼睛晶狀體的組成細胞，可以一生無需進行分裂。減數分裂僅在生殖細胞（精子和卵子）的形成過程中發生，用於性繁殖。
細胞分裂的階段
在進行有絲分裂或減數分裂之前，細胞會經過一個稱為間期的準備過程，其中細胞生長並複製其遺傳信息。
有絲分裂除了間期外，還包括六個階段。前五個階段將細胞核及其遺傳信息分裂成兩半，最後一個步驟將整個母細胞分裂成兩個相同的子細胞。有絲分裂的階段包括：
1. 前期：染色體，其中包含遺傳信息，緊縮並準備與細胞分裂過程中的纖維絲連接。
2. 促中期：通常包含染色體的核膜破裂，纖維絲形成並與染色體結合。
3. 中期：染色體在纖維絲的中央對齊。
4. 後期：染色體分開並向纖維絲的極點移動，同時纖維絲的極點也移開。
5. 末期：兩組分開的染色體周圍形成新的核膜。
6. 細胞質分裂：細胞分裂。
減數分裂與有絲分裂有類似的步驟，但有兩次分裂。第一次分裂產生兩個具有兩套染色體的細胞，就像有絲分裂一樣。第二次分裂創造出四個只包含一套染色體的細胞，因為遺傳信息不會再次複製。減數分裂的一個獨特特點是在第一個前期（前期I）中發生的一個稱為交叉互換的過程。這個過程會將來自不同父母的相應染色體之間的DNA混合在一起，增加了遺傳多樣性。
NIGMS資助的細胞分裂研究
許多由NIGMS支持的科學家致力於細胞分裂的研究。其中一些研究人員正在研究細胞如何通過有絲分裂和減數分裂期間的纖維絲對染色體的排列和分離來維持正常的細胞分裂。另一些則研究如何在減數分裂的交叉互換過程中防止引入遺傳錯誤。還有一些研究則致力於了解細胞是選擇生長和分裂還是進入休眠期的過程，這對於理解由於細胞分裂過多或不足引起的疾病非常重要。
這篇文章簡要介紹了有絲分裂和減數分裂在細胞分裂中的區別。有絲分裂產生遺傳相同的子細胞，而減數分裂產生遺傳不同且只含有一半DNA量的細胞。了解細胞分裂的過程和區別有助於我們更好地理解細胞生物學和遺傳多樣性的形成。同時，NIGMS資助的研究有助於揭示細胞分裂的機制，進一步推動我們對於疾病和遺傳的理解。
折疊內容
There are two kinds of cell division: mitosis and meiosis. What’s the Difference? Mitosis produces two genetically identical “daughter” cells from a single “parent” cell, whereas meiosis produces cells that are genetically unique from the parent and contain only half as much DNA.Sep 8, 2021
Posted on September 8, 2021February 9, 2023Make Like a Cell and Split: Comparing Mitosis and Meiosis by Abbey Bigler11 comments
Your body is made up of trillions of cells that all originate from just one—a fertilized egg. The massive multiplication of cells after conception is possible thanks to cell division, which occurs when one cell splits into two. Cell division not only enables growth but also replaces damaged or dead cells and makes reproduction possible. There are two kinds of cell division: mitosis and meiosis.
Mitosis is shown on the left, and meiosis is shown on the right. Credit: Judith Stoffer. Click to enlarge
What’s the Difference?
Mitosis produces two genetically identical “daughter” cells from a single “parent” cell, whereas meiosis produces cells that are genetically unique from the parent and contain only half as much DNA. Most cells in the body regularly go through mitosis, but some do so more often than others. For instance, those that line the stomach replace themselves after just a few days because they’re subjected to strong digestive acids. In contrast, liver cells may wait up to a year to replace themselves. There are also a few types that last a lifetime without dividing, such as some nerve cells and cells that make up the lens of the eye. Meiosis occurs only in the production of sperm and egg cells for sexual reproduction.
The Phases of Cell Division
Before either mitosis or meiosis occurs, cells go through a preparatory process called interphase, where they grow and make a copy of their genetic information.
Mitosis has six phases apart from interphase. The first five phases divide the nucleus and its genetic information in half, while the final step splits the entire parent cell into two identical daughter cells. The phases of mitosis are:
Prophase: Chromosomes, which contain genetic information, condense and prepare to attach to the spindle—a cellular machine that moves chromosomes during cell division.
Prometaphase: The nuclear membrane—a structure that typically contains the chromosomes—breaks apart, the spindle forms, and chromosomes attach to its strong, hollow fibers.
Metaphase: Chromosomes align along the spindle’s center.
Anaphase: Chromosomes pull apart and move toward the spindle’s poles, which also move apart.
Telophase: New nuclear envelopes form around the two separated sets of chromosomes.
Cytokinesis: Cells divide.
Meiosis has similar steps to mitosis but with two sets of divisions. The first division results in two cells that each have two sets of chromosomes, like in mitosis. The second division creates four cells that each contain one set of chromosomes, because the genetic information isn’t copied a second time. One unique feature of meiosis, which takes place during the first round of prophase (prophase I), is a process called crossing over. DNA is mixed between matching chromosomes from the different parents, increasing the genetic diversity.
NIGMS-Funded Cell Division Research
Many scientists who are supported by NIGMS study cell division. Some of these researchers are investigating how cells:
Maintain normal cell division through aligning and separating chromosomes via the spindle during mitosis and meiosis
Prevent genetic errors from being introduced during crossing over in meiosis
Decide to either grow and divide or enter a resting phase, which is important in understanding diseases caused by excessive or insufficient cell division
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