How Cells Reproduce, and Make Babies. Its Magical.
Once upon a time, you were a cell. As a cell you couldn't move, breathe, talk or hear, but the one thing that you could do is reproduce, and reproduce you did. Starting as one cell and then doubling exponentially until you ended up as a body with 50-75 trillion cells. The processes that control how that original cell is made, and how a person is made from that cell are some of the most important and intricate process in biology.
Then comes metaphase, where the chromosomes lined up across the center of the cell, across what as known as the metaphase plate, by the spindles attached to the centromeres. In anaphase this lining up pays off because, the pairs are then pulled apart by the centromeres to the opposite sides of the cells. In telophase the spindles disappear and the cell membrane starts to split apart into daughter cells. When the cell enters the final stage of mitosis, and the cell cycle, cytokinesis, the cell splits into two daughter cells, each with 23 pairs of chromosomes.
Disclaimer:
Now the first thing that I should explain is how the cell cycle and Mitosis work, as these will be necessary to understand how Meiosis (slightly more complicated than Mitosis) works, and how the baby duplicates its cells to grow in the womb.
Mitosis & The Cell Cycle:
Since Mitosis is a circular cycle (seems redundant right?) Which means the new cycle starts right after the last cycle ended. Now that the last cell cycle has ended our newly created (cloned would be a more accurate term?) cell (let's call it Joe) enters the magical phase of G1 (not G6, G1, that song is just stupid). The G1 phase is all about...you guessed it, Growth! All that the cell does during G1 is get nice and big to prepare to duplicate its chromosomes. This happens in the next stage, aptly named Synthesis. All that happens in this stage is the chromosomes make clones of themselves going from 23 pairs of chromosomes (2 sets of 23) to 46 pairs (4 sets of 23.) From here Joe then enters phase G2, also known as.......wait for it.......wait for it.......wait......GROWTH PHASE TWO!!!!!!! During this phase the cell gets to a large enough size that it cannot efficiently remove waste from the insides, and get "food" in. Which, of course, means it's time to end interphase (the last three phases/stages) and enter...Duh Duh Duh......the Mitotic cycle!!!
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| The Cell Cycle. Obviously. |
This is where the action starts. The mitotic cycle consists of four separate phases: Prophase, Metaphase, Anaphase and Telophase. Prophase, the first phase, is when the chromosomes become visible (under a microscope) and the nucleolus magically dissolves. During this phase the pairs of chromosomes, due to their cloning, are in an "X" shape, where the original, and duplicate are crossed over each other. These pairs are joined to the cells by spindles attached to "Centromere's"
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| "X" shape. |
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| Mitosis-ness....In image form! |
Meiosis & The Beginning of a Baby
When a mommy and a daddy love each other very much, (or 16 year old's want to get popular, yes I do hate MTV's programing) a baby is made. Ok, I'm joking. It's a lot more complicated than that. The process of cellular reproduction starts back when parents are just babies themselves. Creating a sort of never ending cycle of "which came first?" In order to create the cell that replicates into a baby, the parents must have sex cells (called gametes) to produce the sperm and the egg that join up and become a baby. Now, most people know that each cell has 46 chromosomes, organized into 23 pairs. But for a baby to be formed the sperm and egg have to have half that number (23 unpaired chromosomes) this happens through a process called meiosis. As Michael Rees, in his blog post "Cell's: They Reproduce." said:
"First off, the goal of meiosis is to produce a cell with only twenty-three chromosomes so that it can share its chromosomes with another cell in order to produce a cell with unique genes that is then
capable of developing into a baby of the species."
Simply put, Meiosis is Mitosis with an extra division added on to the end, allowing you to get 23 individual chromosomes rather than the 23 pairs normally produced in Mitosis. Meiosis follow's the basic pattern of mitosis, but at the end, it adds in an extra division of the daughter cells. By adding that extra division at the end of the mitotic cycle, the daughter cells of "Joe" do not get to go into synthesis, which then means that they don't double their number of chromosomes, which allows each daughter cell to get split into cells that each contain 23 individual chromosomes. Because sex cells each have 23 chromosomes they are able to combine into one cell with 23 pairs of chromosomes, which then divides by mitosis into more cells, which then create a baby. Simple right?
