Cleavage in Animal Development: Definition, Patterns & Regulation Video

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  • 0:01 Embryonic Development
  • 0:47 Major Events During Cleavage
  • 2:10 Patterns of Cleavage
  • 3:30 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Did you know that you were once just a tiny, single cell? But look at you now - a full grown multicellular being! You can thank cleavage for that, which you'll learn about in this video lesson.

Embryonic Development

You've come a long way from when you were just a zygote. You probably don't remember this stage of your life because you were only a newly fertilized egg in the first stage of being a unique individual. But think about how much has happened to you since then - you developed and grew, you were born, and now here you are, learning about it all!

As a human you are made up of many trillions of cells, but you weren't always this way. The first major stage of development a zygote goes through to help you reach this great cellular height is called cleavage. This is the rapid cell division that leads to a multicellular embryo (to cleave something is to split or slice it). And, this is such an important stage that we've devoted an entire lesson to it! Ready to get started?

Major Events During Cleavage

There are some really important things that happen during cleavage, as well as some processes that are essentially put on hold. The cell is dividing incredibly fast during cleavage, which means that the processes that go along with cell division, such as DNA synthesis, mitosis, and cytokinesis, also occur at rapid-fire speed. But during this time, very few new proteins are made. The embryo also doesn't do much growing in terms of size during cleavage - it stays the same size as the zygote! What happens is that, as the cells continue to divide, they divide into smaller and smaller cells instead of just building up into a larger embryo.

This makes sense if you think about it. If you cut an apple in half, you have divided the apple into two equal segments. Divide each of those two pieces in half and you now have four. But you don't have four larger pieces, just four pieces that add up to the same size as the original apple.

In an embryo, this process continues on and on, with each new cell dividing into smaller cells until a hollow cell ball called a blastula is formed. And inside this ball is a fluid-filled cavity called the blastocoel. Unlike our apple, though (which is now just many equal-sized pieces of one apple), each new cell that is formed from division has its own nucleus and is its own independent cell.

Patterns of Cleavage

Just like animals come in all shapes and sizes, so does the cleavage that creates them. There are two main patterns of cleavage to be familiar with: complete and incomplete. Complete cleavage is also called holoblastic cleavage, and incomplete cleavage is called meroblastic cleavage.

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