Mutations Worksheet - PHH
Name
There are three main types of mutations: point missense mutations, point nonsense mutations, and frameshift
mutations. In each of the following DNA sequences, you will use the mRNA and amino acid sequences to
identify the mutation that occurred and the effects of each on, if any. Look and analyze carefully!
Original DNA Sequence:
mRNA Sequence:
T A C A C C T T G G C G A C G A C T
AUG UGG
Amino Acid Sequence:
Mutated DNA Sequence #1: T A C A T C T T G G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #2: T A C G A C C T T G G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #3: T A C A C C T T A G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #4: T A C A C C T T G G C G A C T A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #1: T A C A C C T T G G G A C G A C T
What will be the corresponding mRNA sequence?
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutations
1. Define Mutation.
2. Which type of mutation results in a different amino acid sequence?
3. Which type of mutation stops the translation of the mRNA early?
4. What type of mutation gives you the exact same amino acid?
Several disorders in humans are caused by the inheritance of genes that have undergone insertions of a
string of 3 or 4 nucleotides repeated over and over. A locus on the human X chromosome contains such a
stretch of nucleotides in which the triplet CGG is repeated (CGGCGGCGGCGG, etc.). The number of CGGs
may be as few as 5 or as many as 50 without causing a harmful phenotype. Even 100 repeats usually
cause no harm.
*What may be an explanation why these repeating nucleotides might not have an effect on the
resulting protein?
The longer repeats have a tendency to grow longer from one generation to the next (to as many as 4000
repeats). This causes a constriction in the X chromosome, which
makes it quite fragile. Males who inherit such a chromosome (only
from their mothers, of course) show a number of harmful
phenotypic effects including mental retardation. Females who
inherit a Fragile X (also from their mothers; males with the
syndrome seldom become fathers) are only mildly affected.
This image shows the pattern of inheritance of the Fragile X
Syndrome in one family. The number of times that the trinucleotide CGG is repeated is given under the symbols. The gene is
on the X chromosome, so women have two copies of it; men have
only one. People with a gene containing 80–90 repeats are normal,
but this gene is unstable, and the number of repeats can increase into the hundreds in their offspring.
Males who inherit such an enlarged gene suffer from the syndrome.
*Why are there more men affected in this family with Fragile X Syndrome than women?