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Transcript of P Katin Cells Cells and More Cells
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e l o IT
. . . . . .
, R.. . .. p b1; . 1m . 1
od
d
I n ~
U on
of S
ovl
d Soc aUf ~ p b
S N
S OS OO2< S 9
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Do you have a mir r
or
at home? Go
and
take a good
look at you rself. h
er
e is your nose, you r
ea
rs, yo ur eyes
and your mouth. the mirro r is large or if you have
al ready crawled up o n a chai r, then you can see yo ur
shoulde rs, you r arms a nd your stomach. Where d id all
those diffe rent
par
ts of you co me from?
h
ey simply
grew. Re memb
er
, yo u w
er
e sma ller on you r last birthday
th an yo u a re now. And you r arms were sma ller, and
your legs, and
your
ears, and eve n you r nose. And two
years ago on you r birthday you w
er
e even smalle r. Y
ou
probably don t remember wha t yo u looked like
thr
ee
yea rs ago.
I bel ieve me and if you don t, ask your
moth
er
, or fa the r or grandmot
her
befo
re
th at you were
very small.
And before that? Befor e that you were very tiny,
smaller han he smallest dot on a p iece of pa per. And
yo u
ca
n t give tha t dot legs or a rms or a nose. Not because
th e pe nc il is too thi ck, but beca use you did n ot hav e th em
th en. And you didn t have
ea
rs, or eyes, or a stomach. .
Yo u
wer
e a
ce
ll. One t iny, litt le cell.
you want
10
know what a cell is and where it came
from, read fur ther.
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Le t s go to th e zoo. First we
wil
visit the lion.
The
re
h
e
i
s
.
L
e
t
s
g
o
c
l
o
s
e
r
.
E
v
e
n
c
l
o
s
e
r
.
D
o
n
t
b
e
a
f
r
a
i
d
,
h
e
i
s
i
n
a
c
a
g
e
T
he
r
e
.
N
o
w
w
e
c
a
n
s
e
e
h
i
s
n
o
s
e
.
L
e
t
s
t
a
k
e
a
m
a
g
n
i
f
y
i
n
g
g
l
a
s
s
a
n
d
l
o
o
k
t
h
r
o
u
g
h
it
.
W
h
a
t
d
o
w
e
s
e
e
?
S
m
o
o
t
h
,
d
a
m
p
s
k
i
n
a
n
d
t
h
a
t
is
a
l
l
.
B
u
t
w
h
a
t
i
f
w
e
h
a
d
m
a
n
y
m
a
g
n
i
f
y
i
n
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g
la
s
s
e
s
a
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w
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l
a
i
d
o
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e
o
n
to
p
o
f
t
h
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o
t
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e
r
?
T
h
en
w
e
w
o
u
l
d
h
a
v
e
a
n
i
n
-
s
t
r
u
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t
c
a
l
l
e
d
a
m
i
c
r
o
s
c
o
pe.
mag n i
i
es every th ing
a
r
o
u
n
d
y
o
u
.
T
h
e
r
e
a
r
e
m
i
c
r
o
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c
o
p
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s
w
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c
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c
a
n
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a
g
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o
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d
r
e
d
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v
e
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o
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th
o
u
s
a
n
d
ti
m
e
s
.
S
o
,
if
w
e
h
a
d
a
m
i
c
r
o
s
c
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e
,
t
h
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n
w
e
w
o
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s
e
e
t
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h
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s
k
i
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o
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o
n
s
n
o
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is
m
a
d
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o
f
s
e
p
a
r
a t
e
l
i
t
tl
e
p
a
r
t
s
,
a
n
d
t
h
e
s
e
p
a
r
ts
a
r
e
c
a
l
l
e
d
c
e
l
l
s
.
Not on ly the lion s nose is m ade of c ells, b
u
t
h
is
t
o
n
g
u
e
a
n
d
t
a
i
l
,
a
n
d
i
n
s
id
e
s
t
o
o
.
A
l
m
o
s
t
e
v
e
r
y
t
h
i
n
g
i
n
t
h
e
li
o
n
s
b
o
d
y
.
A
n
d
th
e
l
io
n
i
s
n
o
t
t
h
e
o
n
l
y
a
n
i
m
a
l
w
it
h
c
e
ll
s
.
E
l
e
-
p
h
a
n
t
s
,
a
n
d
g
i
r
a
f
f
e
s
,
a
n
d
b
e
a
r
s
h
a
v
e
t
h
e
m
to
o
.
A
c
t
u
a
l
l
y
,
e
v
e
r
y
l
i
v
i
n
g
t
h
i
n
g
is
m
a
d
e
a
l
m
o
s
t
e
n
t
i
r
e
l
y
o
f
c
e
ll
s
.
E
v
e
n
g
r
a
s
s
.
E
v
e
n
t
r
e
e
s
.
E
v
e
n
y
o
u
r
g
ra
n
d
m
o
t
h
e
r
.
A
n
d
e
v
e
n
b
u
t
t
h
i
s
is
j
us
t
b
e
tw
e
e
n
u
s
)
y
o
u
r
fa
t
h
e
r
s
n
o
s
e
.
I
w
o
n
d
e
r
how ma ny ce
s his nose h as?
Y
o
u
a
r
e
a
l
s
o
m
a
d
e
o
f
t
h
e
s
e
c
e
l
ls
.
A
n
d
y
o
u
s
t
a
r
t
e
d
o
u
t
a
s
j
u
s
t
o
n
e
.
B
u
t
w
e
w
i
l
l
t
a
l
k
a
b
o
u
t
t
h
a
t
a
li
t
t
l
e
l
a
t
e
r
.
•
•
M
_
•
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·
l
@ _
HOW
BIG ARE CELLS?
Very ve ry sma ll So small that you can only see them
with a microscope A cell
s
a million times sma ller th an
you
are
If
we
co
uld take
ce
lls and put them in a line on
your
rul
er
there would be
abou
t a th ousand of them
between the sma llest divisions on the ruler which is one
millimeter
The
cell is to a gra in of sand what the grain
of sand
s
a wheel on a car Even a tiny dot on a piece
of
pa
p
er
is a lot bigg
er
than the ord ina ry cell
See
how small
cells
are
?
•
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J
WHAT COLOR ARE CELLS
When you go to bed tonight, look at yo urself carefu
ll
y.
You will p
robab
ly nd at least a few da rk spots, or birth-
ma rks, on your skin. They are
dark
because the cells in
them a re full
of
black o r da rk brown matt
er
And you have fed ce lls.
Th
ey
l
oat in your blood. In
each d
rop of
blood there are several million of these ce lls.
If
y
would take them
out
of that drop as is d
one
when
analysing yo ur blood , then the red color would leave the
blood along with those cells. Blood is red because
it
con-
tains red ce
lls
But most cells are colorless and transparent That is
why
ce
lls are colored with a special dye so we can see
them under the microscope. Then they become blue, red,
green and even luminous if they are dipped in special
luminous dye.
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v
W
H
A
T
S
H
P
E
S
A
R
E
C
E
L
L
S
D
i
f
f
e
r
e
n
t
s
h
a
p
e
s
.
T
h
e
r
e
a
r
e
r
o
u
n
d
c
e
l
l
s
w
h
i
c
h
fl
o
a
t
in
t
h
e
b
l
o
o
d
.
A
n
d
n
e
a
r
b
y
t
h
e
r
e
a
r
e
c
e
l
ls
w
h
i
c
h
lo
o
k
l
ik
e
sa uce rs . T hey a
re
t
h
e
c
e
l
l
s
w
h
ic
h
a
r
e
r
e
d
a
n
d
g
iv
e
b
l
o
o
d
i
ts
c
o
l
o
r
.
A
n
d
t
h
e
r
e
a
re
a
t
c
e
ll
s
l
i
k
e
s
h
s
c
a
l
e
s
.
S
k
in
i
s
m
a
d
e
o
f
t
h
e
s
e
.
A
n
d
t
h
e
re
a
r
e
c
e
l
l
s
w
h
i
c
h
r
e
s
e
m
b
l
e
a
c
u
p
.
A
n
d
s
o
m
e
w
h
i
c
h
l
o
o
k
l
i
k
e
a
b
l
o
c
k
.
T
h
e
r
e
a
r
e
e
v
e
n
g
o
b
l
e
t
-
s
h
a
p
e
d
c
e
l
l
s
.
B
u
t
th
a
t
is
n
o
t
a
ll
M
a
n
y
c
e
l
ls
h
a
v
e
l
it
t
l
e
h
a
i
r
s
s
t
i
c
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i
n
g
o
u
t
i
n
d
i
f
fe
r
e
n
t
d
i
r
e
c
t
io
n
s
.
T
h
e
y
a
r
e
e
v
e
n
s
m
a
l
le
r
t
h
a
n
c
e
l
l
s
a
n
d
y
o
u
k
n
o
w
h
o
w
s
m
a
l
l
c
e
l
l
s
a
r
e
l
T
h
e
r
e
a
r
e
a
l
s
o
c
e
ll
s
w
i
t
h
o
n
e
l
o
n
g
t
a
i
l
m
u
c
h
lo
n
g
e
r
t
h
a
n
t
h
e
c
e
ll
i
t
s
e
l
f
.
T
h
e
s
e
c
e
l
l
s
lo
o
k
li
k
e
t
i
n
y
s
n
a
k
e
s
.
S
o
w
h
a
t
s
h
a
p
e
s
a
re
c
e
l
l
s
?
T
h
e
b
e
s
t
a
n
s
w
e
r
i
s
p
ro
b
a
b
l
y
:
a
l
l
s
h
a
p
e
s
.
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WHAT ARE CELLS MADE OF?
Basically cells are made of protein. And they have fat , lik
in soup broth. It even floa ts in the cell like fat in a soup bow
you let sit for too long.
he
outside of cells al
so
have a laye
of t l
Besides protein and fa t,
there
is a lso sugar. In some cell
ther
e is more, in othe rs less. Beets ha ve so much that they ar
even called suga r beets. Sugar which you sprinkle on you
cereal
is
made fr om the cells of these beers.
Cells c
onta
in other substances but th
ere
is
so little of them
thai we
will
not talk about them. Except
for
one.
A person needs all the parts of his body: his
ar
ms, and legs
and stomach. But the most im
po
rtant p
art
is his head and th
brain inside
it.
You see,
it
directs
the
arms, and legs, and even
the stomach. Your bra in remembers wha t h
ap
pen ed yeste rda
and thinks about what to do tomorrow. Wel there is somethin
a litt le like that
in
the cell.
h
is substance looks like thin threads
hin and long. And the
name
of it is long. t is
pro
bably th
longest and most complicated word you have ever heard. t i
de ox
y
ribo nu
-cleic acid.
h
ere
is no t much of it in your cells. Much less than protein
fat and sugar. But it is the most
imponant
substance in you
cells, and we will ta lk about it later. And so we don t have 1
write (
here
we go ) deoxyribonucleic acid
ever
y time,
we
wil
shorten it. We
will
take the rst letter
0 ,
and the letter N from
the middle, and then the lett
er
A instead
of
the word acid . So
from Ihat long word we have only three lette rs DNA. hat i
what eve
ryo
ne calls th is substance. BUI don t forget tha t th i
is only a shonened fo rm of th e real name: deoxyribonuclei
acid.
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HOW ARE CELLS MADE
Cells
ar
e very ve
ry
complicated. So
co
mplicated that no one
knows eve ryt hing
about
how they
ar
e made. Scien tists
ar
e still
trying 10 fi nd out more. For th is there are complicated instru
ments and huge microscopes.
The
y are so big that special build
ings have
be
constructed for them. II is fun ny
thai
in
or
d
er
to see a cell hun
dre
ds of times smaller tha n a gra in of sand we
need a microscope as big as a house But with these microscopes
scientists ha ve been able to
learn
someth ing
abo
ut how a cell is
made.
Let us begin with the outside.
Al
l cells are sur rounded by
a thin covering made of protein and fat. This covering is called
a membrane or a plasma membrane to be more exact. It is so
th in that you can barely see it even with the most powerful
microscope.
if
you look very carefully you will notice that the
line
ac tually two.
The
membrane
ma
de of
two layers -
the
outer and the inner
Though it is very diffic ult to gel a good lo
ok
at the ce ll mem
brane it is still very important . I will te ll you why.
Your mother and fa ther feed you. Sometimes they give you
a delicious pie
and
at ether rimes not so delicious cereal. But
you need eat both because they are good fo r you. T hey
wou ld not give you food that was bad f
or
you.
This is what
rotein
Q cell
or plasma
mem r ne
I
at
s like
•
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·
•
Cells
have
decide
for
themselves what is good for them
and
wha t is harmful. Ma ny different substances float
around
them. But what is
amazi
ng is that only good things get into the
cell. It is the membrane which sees 10 this.
t
allows useful sub-
stances to pass freely
bU
I it
doe
s not lei ha
rmf
ul substances in.
This
means it can
distinguish one substance from another. So
far we know very little of how
it
does this.
But that
is
n all the ce ll membrane can do
When cells touch one anot
her
, thei r membran es slick together.
If they did not do this we wou ld fa ll apart into millions of separate
cells. But a cell on ly sticks to a ce
ll
which is the same kind and
does not stick 10 a cell which is different. Th is m
ean
s the
membr ne c n distinguish one ce
ll
rom nother
So, the outside of a ceU
is
its memb
rane
. And what
is in-
side? Everything that is insi
de
the m
emb
rane
is called eyre-
plasm. t is the maj
or pan of
the cell. And there
is
a reason.
Cytoplasm is like a large factory. T he protein
and
sugar and fat
which cells are made of are all produced in the cytoplasm.
J ust like in a real fac tory, the f nish
ed
products are sent
to different places on order. Some remain in the cytoplasm,
ot hers
ar
e sent f
ur
ther, to the m
embran
e,
and
sti
ll
others
ar
e
sen t out
of
the ce ll like, f
or
examp
le, the sa liva in your
mout
h .
And the substances in a cell a re not the only ones to move in
different directions. T he cell itself does.
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•
Do
you
remember when you cut
you
r fi nger not lo
n
ago
ry
to fi nd the cut. hereis alm ost no sign
of
it. Because cells
moved towards the wou nd fro m a
ll
sides a nd filled
it
up. Your
cut
healed. But ce lls do no t ha ve a r ms a nd legs. In o rder to mo ve they
ha ve to stretch o ne side a nd pull up the o ther like a wo rm . For
this the ce ll has muscles like yo u and I do only they a re ve ry
hin
h
ese are also located in the cytoplas m.
An d
nall y we ha ve co me
to
the most impo rta nt
pan he
nucleus is in th e cytoplas m
and
it contains
the
thi ng the cells need
most. Yo u haven fo r
got
te n a lready ha ve you?
hat
s rig ht
ONA. Something so imp
ortant
must be gua r
de
d. hatis wh y the
nucleus is surro unded by its o wn membr
an
e ca lled a nu cl
ear
membr
an
e or a nuclea r envelope. J ust like
the
cell is. T he
nucleus is much sma lle r than the cell so the l
on
g threads of DNA
a re wrap ped in tigh t bra ids so they ca n a ll 1. hese
ar
e called
chromosomes.
Eac h of you r ce lls has 46 of them. And ea ch of mine does too.
T he cells of
normal people contai n 46 chromosomes. Read th e
next chapter 10 fin d out why we need ch romoso mes.
Nucleus
ow a cell is made
ell orplasma
memb
r n
yt p
asm
Nucleus
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ucle r
membr ne
ucleus
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®
WHY DO WE NEED CHROMOSOMES?
A
mouse
d
oe
s not look like a n el
ephant
a nd a beetle
does not lo
ok
like a co w. No one would mix you up with
the boy next door o r co nfuse him with his broth
er if
they
are not
twin s.
Why is that ? You might say that a mou se is small
and
a n elephant is big
and
has a
tr
unk.
Th
e
oy
ne x t door is
sn ub-nosed a nd has frec kles a nd doe s not loo k a nythi ng
like you . .
And ag ain I ask
why
y doesn t a m
ou
se look like
an elepha nt? Why does the boy next doo r ha ve a snub
nose and freck les
and
yo u don t?
y
don t people look
like one a nothe r? ndwhy don ta nimals?
T h s a depends on chr omosomes. A mouse s chromo
so mes are not like th ose of an elephant and yours
are
not
like those of
the
boy next door. Everything that makes one
living
cr
eature different from another is contained in the
chromosomes. And how th e
ce
lls co me togeth
er
to make
a nose in stead of a stomach . And what color some
one s eyes should be. And th e color of his hair. And
th e sha pe of h is
ea
rs. And th e length of h
s
n
ng
er
s.
All of this infor ma tion is co ntai
ne
d in the chro mo
so mes. .
The
language of chromosomes is
not
simple . And the
re cordings do not loo k anythin g like ou r writing. By the
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way people did not a lways wri te with letters he Chinese
nd
J apanese still use specia l symbols instead of letters
ca lled hieroglyphics And several nationalities in ancien t
times used knots
on
a rope for recording infor
m -
tion
T he c
hro
mosomes look like those kno t recordings
But instead of knots specia l substa nces r e faste ned to the
threads of DNA here a re only fou r of them: adenine
guanine cytosine a nd thymine T hey a re shortened to the
fi
rst letters of
e ch
word: A G C nd T
hey
re like
the letters of the cell alphabet Words re made from these
Only in ou r language words a re
of
diff
er
en t lengths
here re short ones like ca t and long ones like rh inoce-
ros But in the language of chromosomes all the words
have only three letters here is CAG TAG AGA CCC
and m
or
e
oge
the r they f
orm
l
on
g orders showing what
how nd when the cell should do something
he language of chromosomes is very precise
nd
even in the longest recordings there are usually no
mist
k
es
•
]
i
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You a lrea dy know tha t you grew from one single ce ll B how did
that happen? T he ce ll is so
tiny
and look at how big and tall you have
ecome
I will
te ll
you how it happened
h
e cell bega n to divide
irst
into
two and the n the two into four Each of them divided in half again and
th is
went
on and on II is impossible 10
count
how many cells a re in your
body now Pr
obab
ly many millions
And you are still growing Every second the cells in your body con-
tinue to divide and
there are
m
or
e and m
or
e
of
them In your arms and
in
your
le
gs
an
d in your ea rs And each of
those
ce lls has a membrane
citoplasm and a nucleus And in the nucleus the re are 46 chromosomes
And the chromosomes in the new ce lls are exactly like those in th e very
f rst one This is because the cell makes anothe r nucleus membra -
ne cytoplasm and complete set of chromosomes before it divides
So when it does divkle everyth ing is evenly split between
th e
WO
ce lls
h
is way there are ident ical chromosomes in
all
the ce lls and that
means Ihe orders which
are
written on them are also identical
B there is a r iddle The orders are identical but the cells are differ-
ent Some are round ot hers are oval some are black
others
are red
Maybe not everythi ng is written in the ch romosomes? Scie ntists th ink
everything is But some ce lls obey one orde r while othe r ce lls obey
anot
her
We
still
do not kno w everyth ing about how they choose the necessary
order But we need to Because various diseases sta
rt
be
cau
se the cells get
mixed up and do not know which order to follow Perhaps by the lime
you grow up scient ists will have learned 10 manage the disobe dien
ce lls and to save people from many illnesses Maybe you will be the
one to do that
:
_
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ow
U
unt
i to0 0
•
•
t
r
1 .. . .
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HOW ARE CHILDREN MADE
You ca n pa rt ly answer this question yourself. T here was one
single cel l.
It
divided and divided and there were m
or
e a nd more
ce lls until f nally a child was made.
But where d
i
the
fi
r5 cell come f r
om
th
e one th at began
it
all? tcame from two - one from the mother and one from the
father.
Among the millions of cells whi
ch
you r
body
is made of there
are special cells. T hey
can
do things tha t other cells ca nnot.
Th
ey
ca n join and serve as the beginning of a new life. All animals and
all humans have these cells. The jo ining of two of these cells
one from your father and one from your mother created the
one which you began from. Bur before these cells joined into one
both of them had gotten rid of half of their chromosomes
otherwise... Otherwise you wou ld have twice as many as you
need. You would have 92 instead of 46. And that should not
happen.
Now you know that half the chromosomes in your cells came
from your mother and half from your father. But your mothe r got
half of her chromosomes from h
er
mother your grandmother
and half from he r father your grandfather And the same is true
of your father. So some of your chromosomes came from you r
grandmot
he
rs and your grandfathers. And one or two from
your
gr
ea t-grandmothe r. So you sti
ll
look a
l
nle
l
ke her.
And maybe in many years your great-grandson will look
like you.
See how wonderfully everyth ing is done
•
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~ ~
A
BOY OR
A
GIRL
Who will co me f rom that cell, a oy o r a girl? T h is also depends on th e
chromosomes.
When you look at chro mosomes under the micr oscope, you can see
th at th ey are all d ifferent. Some a re sho rt while oth ers are long. So me a re
shaped like sling-sho ts, and ot he rs are straight
ke sticks.
Scientists have not discovered which ch ro mosomes dete rmine the
co lor of your eyes o r the shape
of
yo ur nose. But the chromosomes which
d
eter
mine whet h
er
a child
w
be a girl or a oy a re kn own and e ven ha ve
th eir own names. T hey a re called by letters of the alphabe t. One is the
leite r X, an d the oth er is the letter Y.
Like a ll e ther chromosomes, these two come to you fro m you r par
en
ts.
Th
e X chromosome ca me from you r mothe r. Later you will
e
ab le to say,
whic h c hromosome came from you r fathe r.
You see, both yo u r mother s cells and your father s cells have the X
ch ro mosome. But t he Y ch ro mosome
is only in your
fath
er s cells.
Th
is
c hromosome con ta ins the in
fonn
at ion which makes a boy diff
er
ent fr om
a
girl .
Yo u already kn ow that be for e two cells join togeth er, they ge t rid of
half their chromosomes. In t he moth
er
s cell, on ly an
c hro mosome re
mains because she does not have a Y chromosome ) . B UI in t he father s
cell the re can be either an or a Y chromosome. T h is is what decides who
will be born after a moth er s an d fa the r s cells join.
th e fathe r s
chro mosome joins with the mot
he
r
s, th en the child will be a girl.
But if the Y chro moso me was in th e father s cell, t he n a boy
will
be b
orn
.
Now you can say wh ich ch romosome yo u got from you r fa th er.
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NOW WH T
O YOU KNOW
A great dea l You know that every ving thing is made of
cells.
Y
know tha t cells multiply by dividing in ha lf. You know
that you c me from one single cell that appea red when a cell from
you r fathe r joined with a cell fro m
your
mother. And you have
also lea
rne
d about how a cell is made: a membrane on the outside,
cytoplasm inside, and a nucleus in the cytoplasm. In the nucl
eu
s
re chromosomes containing all the information about what the
cell should do.
See how many interesting th ings you can learn by asking
just one simple question : Where did I come from? And think
how many i
nter
esting things you still do not know. Why does a
cell suddenly begin to divide? How does it
i
ght against h rmfu l
germs? How does a cell move? How do new animals ap pea r if
children always resemble their p rents? Why are plants green
nd
we
r
en
t? Why is a frog cold, while we have a tempera
ture
of
36.6 degrees Celsius if we do not have a feve r? And why do we get
fevers?
Some of these questions do not h ve answers yet. We still
have much to le rn. And 10 do that we must study.
you un-
derstood what was
wr
itten in this book, then you ca n say that you r
studies have begun. Even if you do not rememb
er
ev
er
ythi ng,
that is no problem. Read this book again afte r a wh
e. And maybe
you
will
fi
nd othe r books about the tiny cells which make up grass,
and trees, and you r gr ndmother, and you yourself, and even
(but this is just between us)
your
fathe r s nose.
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