Key area 6: Mutations

1. Key area 6: Mutations

2. Mutations Mutations are a change in the structure or amount of an organism’s DNA. Mutations arise spontaneously and at random.

3. Frequency of mutations Mutations 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.

4. Types of mutation • Single gene mutations • Chromosome structure mutations • Polyploidy

5. 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.

6. (a) Deletion mRNA Met Gln Protein Thr Ser STOP mRNA Met Gln Protein His Leu

7. (b) Insertion mRNA Met Gln Protein Thr Ser STOP mRNA Met Ala Protein Asp Ile Leu

8. (c) Substitution mRNA Met Gln Protein Thr Ser STOP mRNA Met Gln Protein Thr Ser STOP

9. 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

10. 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.

11. 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?

12. 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.

13. 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 haeomoglobin with 4 oxygen carrying subunits Haeomoglobin with only 2 oxygen carrying subunits

14. 2. Chromosome structure mutations

15. (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.

16. (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.

17. 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).

18. 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.

19. (c) Inversion Reverses the normal sequence of genes. This often results in the formation of non-viable gametes.

20. Non-reciprocal translocation

21. Reciprocal translocation

22. 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.

23. 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.

24. 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.

26. Polyploid plants with an uneven number of sets of chromosomes are sterile. This allows the production of seedless fruits. e.g. bananas

27. Polyploidy in animals It 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.