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Transcript 

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A suitcase of clothes
Boxes of household
goods
A fork with coiled
spaghetti
A bundle of rope
A chromosome
Biology
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Chromosomes are
pieces of tightly
packed “supercoiled” DNA.
The DNA is packed
up so it can be
moved easily.
Do you think the
DNA in cells is
packed up in
chromosomes most
of the time?
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Most of the time,
DNA is in long loose
strands, called
chromatin, in the
nucleus.
The DNA needs to
be accessible by
enzymes so it can
replicate and
produce mRNA,
which makes
proteins.
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Like shoes, chromosomes
come in pairs.
Unlike shoes, our pairs of
chromosomes are very
similar, but not always
identical.
Why do you think we have
un-identical chromosomes
that come in pairs?
How many
chromosomes
are pictured?
How many
homologous
pairs are
pictured?
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Chromosomes can be
duplicated
The 2 copies are
identical
The two copies are
called sister chromatids
They are connected at
the center at a point
called the centromere
How many
chromosomes are
pictured here?
How many
chromosomes
are pictured?
How many
homologous
pairs are
pictured?

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Chromosomes
contain many
different genes.
A gene is a
section of DNA
that codes for a
specific protein
or trait.
Example- a
gene that
makes a
protein that
helps blood clot
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Some genes
have different
versions (white
flowers or
purple flowers)
We call the
versions alleles.
Example: the
alleles for hair
color in rabbits
may be white,
brown, etc.
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Many different organisms have
different numbers of
chromosomes.
This makes sense because we all
have different traits, produced by
different proteins, which are
produced by different genes on
your DNA.
Mulberries have 308
chromosomes.
fruit flies have 8.
a dog has 78.
Our closest relatives, chimpanzees
and gorillas both have 48.
Human DNA can be separated
into 46 chromosomes.
 Since chromosomes come in
pairs, humans have 23 pairs of
chromosomes.
 People with Down Syndrome
have 47 chromosomes because
they were born with an extra
copy of chromosome #21.
 They still have 23 pairs of
chromosomes, but one of those
pairs is a “trio” because it has a
3rd chromosome.

MITOSIS
AND
MEIOSIS
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