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) Substitution2) Insertion3) 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) Missense2) Nonsense3) 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 post-transcriptional 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) Duplication2) Deletion3) Inversion4) 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.