Science 9
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Students will be expected to:
 Explain the importance of using the terms
gene and chromosome properly
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The cells of all living things contains DNA
It is a chemical compound that is responsible
for genetic information
Deoxyribonucleic acid
Provides directions that guide the well being of
the cell
Information gets sent from the nucleus to other
parts of the cell by chemical messengers
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It is made up of a series of chemicals called
nitrogen bases, held in a long, winding helix
They are used like letters or characters in a
simple code
There are four characters, or nitrogen bases,
that make up DNA: adenine (A), thymine (T),
cytosine ©, and guanine (G)
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The order in which they appear is the code
Groupings of three bases help to determine the
genetic make up of an individual
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A gene is a section of DNA that determines a
trait or characteristic
In humans, there are over 6 billion nitrogen
bases of DNA
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DNA can make copies of itself in a process
called replication
Cells need to be able to divide in order to
replace dead and worn out cells
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The DNA duplicates itself before a cell divides
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Each cell has a copy of genetic information
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When replicating, the DNA molecule “unzips”
and each side serves as a place to receive a
nitrogen base
Adenine always pairs with thymine
Cytosine always pairs with guanine
By the end of the process, two helixes are
formed
The two new DNA molecules are identical to
each other
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Humans have 46 chromosomes arranged in 23
pairs
One chromosome comes from each parent
The information on one chromosome may be
slightly different from the information of the
other chromosome (differences in the code)
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The DNA contained in your chromosomes is
unique to you
DNA is one way to identify yourself since no
one (except an identical twin) has all the same
DNA as you