Thames & Kosmos Genetics & DNA Lab handleiding

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Thames & Kosmos

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Handleiding

Where are these thousands of programs that

control our bodies and make us who we are

located? To answer that question, let’s take a

brief trip into our own insides. Your body is

made of about 100 trillion cells — that’s

100,000,000,000,000 of them. That’s rather

inconceivable. If you laid them all out in a

straight line, they would stretch out for four

million kilometers, and wrap 100 times

around the world. How did we come to know

all this? Well, why else do we have around 30

billion brain cells? A ﬂy doesn’t have to worry

about this kind of thing, because it only has

around 100,000 cells upstairs.

Cells and

Chromosomes

BRAIN TEASER:

In Experiment 9, which offspring would

surprise the parents?

ANSWER:

Like all animals and plants, humans come

from a single starting cell formed by the

fusion of an egg and a sperm cell. The egg cell

is actually the largest human cell, and at one

tenth of a millimeter in size it is just barely

visible to the naked eye. If it is fertilized by a

sperm cell, it divides in two cells, and then

the two cells divide again and then all those

cells divide — the embryo grows in the

mother’s womb, the baby grows, you grow...

until you are about 18 years old. And even

after that point, many cells in the body keep

dividing, because some are always dying off

and have to be replaced.

A skin cell on your ear lobe lives for one

month, one on your belly a little over two

weeks, yet other cells, such as the ones on

your bottom, just live four days. Every

second, about 50 million cells die inside us

and on us, and if they are outside on our skin,

they simply fall off, and we leave behind as a

kind of cellular trace showing where we have

gone and been. And when you scrape your

knee, you might lose several million cells in

one fell swoop in a few drops of blood. They,

too, will be immediately replaced: By other

blood cells, which divide and divide and

divide...

→ → →

Cells and Chromosomes | 19

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