Transcript Changes in DNA

Changes in
DNA
Analogy

We will be using a sentence as an analogy to
represent a strand of DNA.

Our sentence is:
The fat cat ate the wee rat.
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If this sentence represents a strand of DNA,
what does each word represent?
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What does each letter represent?
Mutations?!?
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Now, we’re going to look at mutations in
the DNA.
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When you hear about mutations, you may
think about some teenage turtles or
growing an extra arm, but the word
mutate just means change. Let’s look at
what happens when we change the
sentence/DNA.
Substitution
The fat cat ate the wee rat.
The fat cat ate the wet rat.
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What changed?
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What does this represent?

How would this type of change affect the
protein?
Deletion
The fat cat ate the wee rat.
The fat cat att hew eer at.
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What changed?

What does this represent?

How would this type of change affect the
protein?
Insertion
The fat cat ate the wee rat.
The fab tca tat eth ewe era t.
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What changed?

How would this type of change affect the
protein?
Point Mutations vs.
Frameshift Mutations
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The substitution example was a point mutation.
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These last two examples of deletion and insertion
were frameshift mutations.
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What’s the difference between a point mutation
and frameshift mutation?

Which has the most significant impact on the
protein? Why?
Synonymous (“Silent”) Point
Mutations

What do you think a synonymous (“silent”) point
mutation can cause?
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Do not cause a change in the amino acid sequence
Generally, do not cause a change in the protein—
however, can reduce the amount of a specific
protein the cell makes or cause the structure of the
protein to be changed in a manner that disrupts its
functioning in the body
Example:

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TAT changed to TAC—both still code from Tyrosine
CTC changed to CTA—both still code for Leucine
Inversion
The fat cat ate the wee rat.
The fat tar eew eht eta tac.
 What
 How
changed?
would this type of change affect the
protein?
Chromosomal Mutations
• What changed?
• How would this type of
change affect the
protein?
Chromosomal Mutations
• What changed?
• How would this type of
change affect the
protein?
Chromosomal Mutations
• What changed?
• How would this
type of change
affect the
protein?
Non-Disjunction
Ex: Trisomy 21 or Down Syndrome

Sometimes, there is an
error in meiosis when
egg or sperm cells
divide resulting in too
many or too few
chromosomes.
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How do you think this
type of change would
impact an organism?
Mutation Impact
 The
impact of a mutation on an individual also
depends on where and when it occurs.
 If
there was a mutation in the DNA of a zygote,
how would that impact the individual?
 How
might a mutation in a skin cell affect an
individual?
Pedigree Charts
 Pedigree
charts are like a genetic family tree.
 They
can use family information to trace genetic
conditions that have been passed along in the
family (genetic conditions caused by
mutations).
 Genetic
counselors use them to help people
analyze their family history and determine the
probability of them having or passing on a
particular condition (mutation).
Pedigree Chart Symbols
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Empty Square = male
Empty Circle = female
Filled/Darkened Square = affected male
Filled/Darkened Circle = affected female
Square/Circle with Slash through =
deceased individual
Pedigree Chart Example