Post on 19-Dec-2015
transcript
Unit 1: DNA and the Genome
Key area 6: Mutations
CFE Higher BiologyDNA and
the Genome
Mutations
Mutations are a change in the structure or amount of an organism’s DNA.
Mutations arise spontaneously and at random.
CFE Higher BiologyDNA and
the Genome
Frequency of mutationsMutations are rare.
In humans it is estimated that there is 1 mutation per 15-30 million base pairs.
Mutation rates differ in different genes and different organisms.
CFE Higher BiologyDNA and
the Genome
Types of mutation
1. Single gene mutations2. Chromosome structure mutations3. Polyploidy
CFE Higher BiologyDNA and
the Genome
1. Single gene mutations
These mutations involve a change in one of the base pairs in the DNA sequence of a single gene. Also known as point mutations.These may occur in the protein-coding sequence or the regulatory sequences which control expression of the gene.
CFE Higher BiologyDNA and
the Genome
(a) Deletion
Met Gln Thr Ser STOP
mRNA
Protein
Met Gln His Leu
mRNA
Protein
CFE Higher BiologyDNA and
the Genome
(b) Insertion
Met Gln Thr Ser STOP
mRNA
Protein
Met Ala Asp Ile Leu
mRNA
Protein
CFE Higher BiologyDNA and
the Genome
(c) Substitution
Met Gln Thr Ser STOP
mRNA
Protein
Met Gln Thr Ser STOP
mRNA
Protein
CFE Higher BiologyDNA and
the Genome
Write a description of each type of mutation:
Insertion, deletion, substitution.
Use the following sequences as your original DNA sequence:
T A G C C G T A T C G T A
CFE Higher BiologyDNA and
the Genome
The impact of point mutations
Research and produce a A3 poster on what is meant by:•Silent mutations•Neutral mutations•Missense mutations•Nonsense mutations•Frameshift mutations
Use diagrams to demonstrate the effects of each mutation on the resulting protein sequence.
CFE Higher BiologyDNA and
the Genome
Case Study: Sickle cell anaemia
• What type of mutation causes this disease?
• Are any of the mutations confined to a specific area or ethnic race?
• What are the symptoms associated with each mutation?
• Are any of the mutations beneficial or are they detrimental?
CFE Higher BiologyDNA and
the Genome
Splice site mutations
RNA splicing is important in creating the mature mRNA transcript.Mutations in the area that marks the start or end of an intron, may lead to one or more introns not being removed. This will lead to a creation of a protein that does not function properly.
CFE Higher BiologyDNA and
the Genome
Thalassemia, a disease caused by a defect in haemoglobin synthesis, is caused by a splice site mutation.
Intron Exon
Normal splicing Abnormal splicing
Normal functional haemoglobin with 4 oxygen carrying subunits
Haemoglobin with only 2 oxygen carrying subunits
CFE Higher BiologyDNA and
the Genome
2. Chromosome structure mutations
CFE Higher BiologyDNA and
the Genome
(a) Deletion
Deletion mutations have a drastic effect on the organism – as genes are lost.e.g. Deletion of part of chromosome 5 leads to Cri du Chat syndrome.
CFE Higher BiologyDNA and
the Genome
(b) Duplication
This results in a set of genes being repeated. Some duplications can be detrimental.e.g. Duplication of oncogenes is a common cause of cancer.
CFE Higher BiologyDNA and
the Genome
Evolutionary importance of gene duplication
Duplication of a gene produces a second copy of the gene which is free from selection pressure (it can become altered with out affecting the original gene’s function).
CFE Higher BiologyDNA and
the Genome
This means it can mutate to produce new DNA sequences.This may confer advantages to the organism and possibly increase it fitness and chances of survival.
CFE Higher BiologyDNA and
the Genome
(c) Inversion
Reverses the normal sequence of genes. This often results in the formation of non-viable gametes.
CFE Higher BiologyDNA and
the Genome
Non-reciprocal translocation
CFE Higher BiologyDNA and
the Genome
Reciprocal translocation
CFE Higher BiologyDNA and
the Genome
Translocation involves transfer of genes from one chromosome to another.
This results in problems pairing chromosomes during gamete formation and leads to non-viable gametes.
CFE Higher BiologyDNA and
the Genome
3. Polyploidy
Polyploidy is duplication of all the chromosomes – resulting in extra sets of chromosomes.
It is the result of an error during gamete formation.
CFE Higher BiologyDNA and
the Genome
Polyploidy in plants
Roughly 50% of plant species are polyploid.
Polyploid plants are normally larger, and have increased seed and fruit size. This is of economic importance.
CFE Higher BiologyDNA and
the Genome
CFE Higher BiologyDNA and
the Genome
Polyploid plants with an uneven number of sets of chromosomes are sterile. This allows the production of seedless fruits.e.g. bananas
CFE Higher BiologyDNA and
the Genome
Polyploidy in animalsIt is thought that polyploidy contributed to the evolution of vertebrate animals.However, mammals which are polyploid fail to survive.Except: Plains Viscacha rat of Argentina.