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Molecular Genetics

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Mitosis versus Meiosis

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A la Shmoop

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So we're here talking about DNA replication now

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with Dr. Ruth Tennen, who is a guru on the subject.

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So, Dr. Ruth, what are the two main types of cells

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in the human body?

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So there's two types.

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One is the somatic cell.

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So, those are kind of the regular cells that you think about.

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So, your liver cells or your skin cells. Muscle cells.

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The other type is germ cells, or sex cells.

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And those are the cells that combine to form a new human. [egg and sperm combine to make a new human]

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[ crowd oohs ]

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Got it. So "somatic" - S-O-M-A-T-I-C.

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Where does that -- what's "som"?

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- It's not from "South and Market," right? - No.

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It was done before that.

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What is somatic?

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So "soma" means body.

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So it's basically body cells.

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Got it.

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Okay. So how do somatic cells relate with germ cells?

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Are they sort of coopetition? Are they frenemies?

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Are they just -- do they hate each other?

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Do they live separately?

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They're pretty happy together. They're in different parts --

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So, basically, your whole body is composed of somatic cells

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and then just sperm and egg cells.

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Those are the only germ cells you have.

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And the germ cells are what ultimately combine to form your body.

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So they're required to form the somatic cells also.

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And how does a germ cell -- cause, you know,

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a normal person, you think "germ, ooh, that's bad.

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I wanna not have any germs."

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But, in fact, that would be bad, right?

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Bad to not have germ cells, yeah.

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It would be difficult to reproduce if you were a human.

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Hmm. So we need the germs to reproduce?

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- Right. - That just seems counterintuitive, but take it. There.

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Okay, next. Five-dollar word - mitosis.

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We touched on this a little bit earlier.

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But give us a good definition for mitosis.

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So, mitosis is the process of cell division that somatic cells undergo. [cells divide]

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They take their duplicated DNA and they divide it into two new daughter cells.

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[ ding! ]

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Got it. So this is like the pants zipper thing

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with the ATCG?

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So, it's a little bit after that.

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During -- if you think about the cell cycle,

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which is basically how a cell goes from one to two cells,

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it starts off by replicating its DNA.

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And then at another point in the cycle is when the mitosis happens.

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And mitosis is just basically the physical separation

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of the DNA into two daughter cells.

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Got it. Okay.

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Then what's "meiosis"? M-E-I-O-S-I-S.

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"Me-osis" or "my-osis" is basically the same idea as mitosis,

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but it's for the germ cells, or the sex cells. [egg and sperm]

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And it's a little bit different because meiosis starts with

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- a normal cell that has two copies of every gene. - Mm-hmm.

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And then there are two stages of meiosis -

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one and two. And, ultimately, at the end, you end up,

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rather than having two copies, just having one copy of each gene in the cell.

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And that's what the egg and the sperm are.

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One copy that can combine to ultimately form a diploid cell.

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Got it. Fair enough.

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Okay. Wow. DNA replication.

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A la Dr. Ruth.

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What are the two main types of cells in the human body?

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What is mitosis?

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What is meiosis?

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