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GENETIC MUTATIONS
Introduction
Deviations from the expected chromosomal number, or mutations in the structure of a gene or chromosome,
are inherited in predictable Mendelian fashion; they often result in dead organisms or substantial changes in
phenotype.
For example, Aneuploidy is the gain or loss of one or more chromosomes from the diploid (paired
chromosomes) amount, resulting in conditions of monosomy(singles), trisomy (triples), tetrasomy (quadruples).
Down syndrome is caused by the trisomy of chromosome #21 in humans. (having 3 copies of chromosome
#21)
Often, a change in chromosome number or in the arrangement of the nucleotides in a gene, results in
phenotypic variation or disruption of development of an organism. Such phenotypic variations are passed to
offspring in a predictable manner, resulting in many interesting genetic situations.
(A) GENE MUTATIONS
1. Define a mutation.
A change to the genetic material (DNA) of an
organism.
4. Define and illustrate a frame shift mutation.
A type of mutation that involves an insertion or
deletion. Usually results in a shift of all nucleotides
to the right, or left, after the location where the
mutation occurred. This usually causes a dramatic
change in the mRNA codons of the gene(s).
Deletion is illustrated below (Second “T” was
deleted)
2. Define mutagen. Give three examples.
Normal DNA:
Anything that can cause a change (or mutation) in
the genetic material of a living cell
Mutated DNA: A T C G C A T C G G C A C T
Ex.) Dioxins, benzene, UV light, asbestos, DDT
pesticide, cigarette smoke, x-rays, poor nutrition
ATCGCTATCGGCACT
5. Describe 2 ways that DNA can mutate without
affecting the phenotype.
(1) Substitution which creates a codon for the same
amino acid
ex) CUU  CUC (still codes for Leucine)
3. Define and illustrate a point mutation.
(2) Inversion that flips a segment of genes that are a
mirror image of each other.
ex) CTGTC  CTGTC (flipping causes no change)
A type of mutation that involves changing a single
base in a DNA sequence. Generally involve a
substitution, insertion, or deletion.
6. Why do you think that an excess of genetic
material is usually less harmful to health than a
deficit?
Substitution is illustrated below (“T” was changed
to an “A”)
If a gene is deleted, that means the cell will not be
able to produce the protein that the gene codes for.
Normal DNA:
If you have extra genes, the cell can still produce the
protein that the gene codes for. Often, too much
protein could be produced which could cause
problems.
ATCGCTATCGGCACT
Mutated DNA: A T C G C A A T C G G C A C T
Note: Questions #7 - #13 refer to the DNA master
strand listed below:
AATGCCAGTGGTTCGCAC
7. Write the nitrogen base sequence of the
complementary DNA strand.
TTACGGTCACCAAGCGTG
Note: Questions: #14 - #21 refer to the DNA
master strand listed below:
AATGCCAGTGGTTCGCAC
14. If a `G' were added to the original master strand
of DNA after the third nucleotide (T), what
would the resulting mutated mRNA sequence
be?
UUACCGGUCACCAAGCGUG
8. Write the nitrogen base sequence of the strand
of mRNA read from the master strand of DNA.
UUACGGUCACCAAGCGUG
9. Write the polypeptide (amino acid sequence)
that results from this DNA master strand.
Leucine – Arginine – Serine – Proline – Serine Valine
10. If the seventh nucleotide in the original master
strand of DNA were changed from A to T, what
would the resulting new mRNA be?
UUACGGACACCAAGCGUG
11. Write the polypeptide (amino acid sequence)
that results from the mRNA molecule described
in #10.
Leucine – Arginine – Threonine – Proline – Serine Valine
12. Draw a circle around the amino acid in #11 that
changed as a result of the mutation described
in #10.
13. Name and describe the type of mutation
described in #10.
Substitution. One letter (nucleotide) was changed
into another letter (nucleotide)
15. Write the polypeptide (amino acid sequence)
that results from the mRNA molecule described
in #14.
Leucine – Proline – Valine – Threonine – Lysine –
Arginine - ...
16. Compare your above polypeptide with the
polypeptide in question #9. Explain how the
polypeptide (amino acid sequence) in #15 has
changed as a result of the mutation described
in #14.
The amino acid sequence in the polypeptide is
completely different, except for the first one (Leucine).
Since all the letters where shifted to the RIGHT, all the
codons have changed.
17. Name and describe the kind of mutation
described in #14.
Insertion. One amino acid was added to the sequence
resulting in a frameshift to the right.
18. Looking at the original DNA sequence…if the
`G' in the fourth nucleotide position were
to be cut out of the original DNA strand, what
would the resulting mRNA look like?
UUAGGUCACCAAGCGUG
19. Write the protein fragment (amino acid chain)
that would result from the DNA molecule
described in #18.
Leucine – Glycine – Histidine – Glutamine –
Alanine – ...
20. Explain how the protein fragment (amino acid
chain) in #19 has changed as a result of the
mutation described in #18.
The amino acid sequence in the polypeptide is
completely different, except for the first one (Leucine).
Since all the letters where shifted to the LEFT, all the
codons have changed.
Also, the amino acid sequence is shorter by one amino
acid
21. Name and describe the kind of mutation
described in #18.
Deletion. One amino acid was removed from the
sequence resulting in a frameshift to the left..
Note: Questions #22 - #33 refer to the DNA master
strand listed below:
25. Write the new nitrogen base sequence of the
strand of mRNA read from the mutated strand
of DNA from #24.
AUCGGCUGGCUAUGCACG
26. Write the polypeptide (amino acid sequence)
that results from this mutated mRNA strand.
Isoleucine – Glycine – Tryptophan – Leucine –
Cysteine – Threonine
27. Describe one similarity between the original
mRNA strand and the mutated mRNA strand
Same length.
Same first 3 nucleotides
Same last 9 nucleotides
TAGCCAGCCGATACGTG C
22. Write the nitrogen base sequence of the strand
of mRNA read from the master strand of DNA.
AUCGGUCGGCUAUGCACG
28. Describe one difference between the original
mRNA strand and the mutated mRNA strand
Nucleotides #4 – 9 have a different order/sequence.
23. Write the polypeptide (amino acid sequence)
that results from this DNA master strand.
Isoleucine – Glycine – Arginine – Leucine – Cysteine
– Threonine
24. If the nucleotides between positions 4 – 9 went
through an inversion, what would the new
DNA sequence be?
TAGCCGACCGATACGTGC
29. Why do geneticists consider inversion
mutations NOT as serious as deletions or
insertions.
Since no nucleotides are lost or gained, NO
FRAMESHIFT occurs. Therefore all codons before
and after the inversion remain the same. Only the
codons within the inverted region are changed.
(B) CHROMOSOME MUTATIONS
Examine the following chromosomal mutations. In the table below, match the appropriate picture to the
chromosome mutation name. Then describe what happens in each of the chromosomal mutations. Extra
information can be found in Chapter 24 in your textbook.
B
A
E
D
C
F
G
LETTER
CHROMOSOME
MUTATION
Inversion
D
Polyploidy
G
Translocation
E
Trisomy
F
Deletion
A
Genes D through F are flipped over, changing the order of the genes on the
chromosome.
Number of chromosomes has been increased to many times the normal amount
Segment of chromosome (genes J & K) has been moved from one chromosome to
another chromosome.
Number of chromosomes has been increased from the normal 2 (pair) to a 3
(triplet). Ex. Down Syndrome (3 copies of chromosome #21 are present)
Segment of chromosome (genes D through G) have been removed/lost.
Duplication
Extra copies of genes have been inserted into the chromosome. Chromosome
now has 2 copies of genes C and D.
Monosomy
Number of chromosomes has been reduced from the normal 2 (pair) down to 1
(single). Ex. Turner’s Syndrome (only 1 X-chromosome)
B
C
DEFINITION/DESCRIPTION