Key Area 1.6 (a) and (b)
Gene Mutations
Learning Outcomes
Genetic Variation
• Within the human population, there are
many different types of variation in the
genomes.
• These difference are the result of
mutations and rearrangements of parts
of the sequence of bases.
Mutations
• Mutations are changes in the genome
that can result in no protein or an
altered protein being expressed.
• Mutations arise spontaneously and at
random but only occur rarely.
Single Gene (point) Mutations
• A single gene (point) mutation involves a
change in one of the base pairs in the
DNA sequence of a single gene.
• A point mutation can alter the
expression of the gene.
Single Gene Mutations
• Three types of single gene mutation are:
1) Substitution
2) Insertion
3) Deletion
Each of these results in one or more
codons for one or more amino acids being
altered.
Task
• Using the text book (page 61), add a
diagram of each type of mutation into
your notes.
• Ask your partner to check over it to
make sure it is fully completed and to a
high standard.
Impact of Protein Structure
• Single-nucleotide substitutions brings
about only a minor change (one
different amino acid).
• Single-nucleotide substitutions include:
1) Missense
2) Nonsense
3) Splice-Site
Missense
• Following a substitution, the altered
codon codes for an amino acid which still
makes sense but not the original sense.
Nonsense
• As a result of a substitution, a codon
that used to code for an amino acid
becomes changed into one that acts as a
stop codon.
• It causes protein synthesis to be halted
prematurely and results in the
formation of a polypeptide chain which
is shorter than the normal one.
Splice-Site
• A molecule of primary mRNA transcript
is spliced to remove introns and seal
exons together.
• A splice-site mutation substitutes,
inserts or deletes one or more
nucleotides at a site where introns are
normally removed.
• Splice-site mutations can alter posttranscriptional processing.
Research Task
• Research reasons for geographical
variation in incidence of post-weaning
lactose tolerance or sickle-cell trait in
humans.
Frame-shift Mutations
• Insertion and deletion both lead to
major changes since each cause a large
portion of gene’s DNA to be misread.
• The protein produced differs from the
normal protein by many amino acids and
it is usually non-functional.
• Frame-shift mutations can also result in
an expansion of a nucleotide sequence
repeat.
Starter/Task
Key Area 1.6 (c), (d) and (e)
Chromosome Mutations
Learning Outcomes
Chromosome Mutations
• These mutation alter the structure of
one or more chromosomes.
• There are four types of chromosome
mutations:
1) Duplication
2) Deletion
3) Inversion
4) Translocation
Duplication
• A segment of genes is repeated.
• Some duplication of genes may have a
detrimental effect or be of an
advantage.
Deletion
• A segment of genes becomes detached
and the two remaining ends join giving a
shorter chromosome lacked the
detached genes.
• Deletion normally has drastic effects on
the organism involved.
Inversion
• A segment of genes is reversed.
• This results in non-viable gametes.
Translocation
• A section of one chromosome breaks
off and attaches to another
chromosome that is not it’s matching
partner.
• Translocation leads to non-viable
gametes.
Task
• Using page 67-69, add diagrams of each
type of chromosome mutation to your
notes.
Importance of Mutations
• Mutation is the only source of new
variation.
• New alleles of genes arise.
• Most mutations are harmful or lethal,
but rarely, can be advantageous.
• Mutations are the raw material of
evolution!!!
Polyploidy
• Polyploidy is the result of an error
occurring during gamete formation or
cell division and all the matching
chromosomes fail to separate.
• Polyploidy is a mutation where cells
receive one or more extra sets of
chromosomes.
Think and Discuss
• Would you ever eat a polyploidy fruit or
vegetable?
• What do you think it would look
like/taste like?
Polyploidy in Plants
• Approximately 50% of plant species are
polyploid, due to duplication of entire
genomes millions of years ago, in their
common ancestors.
Importance of Polyploidy
• Polyploid plants are larger, have
increased seed and fruit size, and
higher yields.
• Polyploid plants with an uneven number
of sets of chromosomes are sterile so
produce seedless fruit.
• Advantages are increased vigour, crop
quality and resistance to disease.
Examples of Polyploid
• Banana – a triploid, originated from a
cross between two species or wild
banana. Bananas are propagated
asexually.
• Potato – a tetraploid, native to South
America.
• Other examples include swede, oil seed
rape, wheat and strawberry.