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Aim
How is DNA coded
for traits?
What is Genetics?
• The branch of
biology that
studies genes,
heredity and
variation of
organisms
Heredity
For offspring to resemble their parents, there
must be a reliable way to transfer
information from one generation to the
next. Heredity is that passage of these
instructions from one generation to another
Traits
• Physical Attributes or characteristic
– Example: hair color, eye color, height
What is DNA?
Every organism requires
a set of coded
instructions for
specifying its traits. DNA
• Contains coded
instructions for inherited
traits
• Contains code for making
proteins
Genes
Genes
A set of DNA
strands that are
responsible for
traits. One or
more genes
determine a
trait
Chromosomes
• There are 46
chromosomes in
the nucleus.
Chromosomes are x
shaped and contain
thousands of
genes.
Largest to smallest
•
•
•
•
Cell
Nucleus
Chromosome
Gene
Where do organism receive their heredity in
sexual reproduction?
• You will receive
half the code
from your mother
and half the code
from your father.
23
23
• Leads to variety
Double stranded-looks like a
latter (Sides & Rungs)
Sides:
• Phosphoric Acid
• Sugar
Rungs(steps)
• A-T
• G-C
Base Pairs
Connect two sides
5
The molecular bases
The most common molecular bases are
Adenine
(A)
Thymine
(T)
Cytosine
(C)
Guanine
(G)
10
Bonding 1
The bases always pair up in the same way
Adenine forms a bond with Thymine
Adenine
Thymine
and Cytosine bonds with Guanine
Cytosine
A-T
Guanine
C-G
Base sequence is important
• Base sequence
determines kind of
gene an organism
possesses
• If the base
sequence changes,
trait also changes
• The gene expression
changes
Hair color gene -Brown
1. If Strand I in the diagram represents a segment of a
replicating DNA molecule with bases A-T-C-C-G-A, the
complementary DNA strand would contain the bases
1.T-A-G-G-C-T
2.T-U-G-G-C-T
3.U-A-G-G-C-U
4.A-T-G-G-C-T
2. The type of molecule represented above is found in
organisms.
Which statement correctly describes the sequence of bases
found in this type of molecule?
1.It changes every time it replicates.
2.It determines the characteristics that will be inherited.
3.It is exactly the same in all organisms.
4.It directly controls the synthesis of starch within a cell
3. Which statements best describe the relationship
between the terms chromosomes, genes, and nuclei?
1.Chromosomes are found on genes. Genes are found in
nuclei.
2.Chromosomes are found in nuclei. Nuclei are found in
genes.
3.Genes are found on chromosomes. Chromosomes are
found in nuclei.
4.Genes are found in nuclei. Nuclei are found in
chromosomes
4. The diagram below represents the banding
pattern for human chromosome 11, with some of
the bands labeled.
The bands represent
1.proteins
2.genes
3.starches
4.enzymes
5. What determines the kind of genes an
organism possesses?
1.type of amino acids in the cells of the
organism
2.sequence of the subunits A, T, C, and G
in the DNA of the organism
3.size of simple sugar molecules in the
organs of the organism
4.shape of the protein molecules in the
organelles of the organism
What is replication?
• DNA must copy
before cells
divide. This is
called replication
• Nucleus can
then divide. This
is called mitosis
Steps for DNA replication:
1.
2.
3.
DNA untwists and
separate
DNA copies
(replication)using
each strand as a
template
2 strands twist
into helix
Step 1- DNA separates
Separation occurs at base
pairs
• Separation
occurs at the
molecular base
pairs. It is
indicated by the
arrow in the
picture to the left
Two templates are created
• These templates
will now
determine the
order of the new
base pairs
created
2 templates
Step 2- Two new DNA molecules
are created
• Replication
produces two
identical
strands of DNA
When does DNA need to copy?
For cell division to occur
Mitosis
Meiosis