Differential Gene Expression: Definition & Examples

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  • 0:00 Differential Gene Expression
  • 0:52 Cells and the Genome
  • 3:21 The Practical Application
  • 5:01 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

In this lesson, explore the theory of differential gene expression and discover what it means in terms of how different cells are formed, how DNA is stored, and how to clone a sheep.

Differential Gene Expression

Growing up, did anybody ever tell you that you can be anything you wanted to be? It's a very inspiring thing to hear. And as it turns out, the ability to become almost anything is actually encoded into our DNA. Granted, we are talking about a cell's ability to turn into part of a kidney or a liver, not an astronaut or ballerina. But the idea is the same.

You see, when cells divide the resulting new cell has a purpose, a function. And the cell arrives at that function through differential gene expression, the activation of different genes within a cell that define its purpose. Is this a skin cell? A muscle cell? A brain cell?

The process of differential gene expression is how cells grow up and determine just what they are going to be.

Cells and the Genome

Let's back up just a little bit and talk about cells themselves. This on the left is a red blood cell. And over here on the right, this is a brain cell. They look different and they have different functions because each one relies on a different set of active genes that define it. But if we zoom in all the way to the molecular level, well, these two cells look exactly identical, and they are.

You see, within the nucleus of the cell is more than just those few genes that define this individual cell. In fact, this nucleus holds an entire genome, the entire DNA sequence for that individual. This is true of every single somatic cell in the body which is basically every cell except sperm or egg cells.

Whether we're comparing a human brain cell or kidney cell or muscle cell or a toenail cell, encoded in the nucleus is your entire DNA sequence. This is where differential gene expression comes in. Practically every single cell in your body contains the genes for the protein hemoglobin. So why is it that only red blood cells are able to actually make it? Hemoglobin only comes from red blood cells and that's because during the process of differential gene expression those genes were activated, defining this type of cell. The genes to produce hemoglobin are not activated in a brain cell or muscle cell -- just in red blood cells.

This process is how all of the different cells in your body define their purpose. Differential gene expression theory was first proposed in the 1960s and since then has become the accepted standard based around three main points.

First, every cell contains the complete genome, which means that the difference between cells is not due to the genes present within the nucleus but through the expression of those genes.

Second, only a small percentage of the genome is expressed in each cell.

And the third argument of differential gene expression theory is that the unused genes within a cell are not destroyed.

The genes from making hemoglobin still exist in your brain cells, even if they aren't being expressed. They're just being stored, just in case. So a newborn cell really can be potentially anything when it grows up. It's just a matter of expressing the right genes.

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