Cellular reproduction requires many intricate steps. In this lesson, we will explore the step known as prophase to gain an understanding of what is happening inside our cells.
Definition of Prophase
Two types of cell division occur in all living things. They are known as mitosis and meiosis. Mitosis is the type of cell division that produces new body cells for every part of our bodies.
These could be skin cells, blood cells, cells that make up various tissues, and so on. Meiosis is the type of cell division that exclusively produces sex cells (either sperm or eggs). Prophase is the first step of mitosis, during which the cell’s chromatin condenses into chromosomes.
There are also two stages of prophase in the process of meiosis.
Prophase in Mitosis
Prophase is the first stage of mitosis. It is the stage of mitosis where the cell spends most of its time. Approximately 80% of the cell’s time of mitosis is spent in prophase, while the remainder of the steps take up the other 20%.
At the beginning of prophase, the membrane that surrounds the nucleus disintegrates. This allows the chromatin to be exposed and worked with during the remainder of prophase. Chromatin is a material made of loose strands of DNA. In this stage, the cell’s chromatin tightens, or condenses, into chromosomes, giving them a shape like an ‘X.’This leaves each chromosome with a complete copy of the genetic material of the individual. This means that every cell in our body has chromosomes that contain our genetic material as a result of the prophase stage of mitosis.
At the end of prophase, a structure called the mitotic spindle begins to form. This structure is crucial to the entire process of mitosis because it will work later in the process to pull the newly formed chromosomes to each end of the cell before it later divides and forms two cells.
Prophase in Meiosis
Meiosis is the process that produces sex cells that will carry the genetic information during the process of reproduction to form the new individual. During meiosis, prophase is divided into prophase one and prophase two. During prophase one, the chromosomes group together into pairs. While they are together, a process called crossing over occurs. This is where the legs of the X-shaped chromosome overlap and exchange genetic information.
Crossing over is very important because it provides genetic variation by randomly allowing the genes from two chromosomes to be exchanged. At the end of prophase one, the nuclear envelope begins to break down to allow the chromosomes to be moved to opposite ends of the cell before division occurs.