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Mutations.  A mutation is a change in the normal DNA sequence.  They are usually neutral, having no effect on the fitness of the organism. General types.

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Presentation on theme: "Mutations.  A mutation is a change in the normal DNA sequence.  They are usually neutral, having no effect on the fitness of the organism. General types."— Presentation transcript:

1 Mutations

2  A mutation is a change in the normal DNA sequence.  They are usually neutral, having no effect on the fitness of the organism. General types of Mutations

3 Introduction  Or they are harmful, and are responsible for many disorders.

4 General types of Mutations  Sometimes, beneficial mutations occur, which cause the “mutants” to better survive in their environment.  These mutations lead to adaptations and are the basis for the theory of Evolution by Natural Selection.

5 There are 2 General Categories of Mutations  Single gene Mutations  Changes in nucleotide sequence of one-gene  Chromosomal Mutations  Changes in chromosomes, involve many genes

6 Types of Single Gene Mutations

7 A) Point mutations  a change in one nucleotide OR base pair in a gene  Often involves a substitution mutation where one base pair is switched for another.  Can also be a single base pair insertion or deletion.

8  Usually occur due to an uncorrected mistake in DNA replication.  Insertions can be fixed by exonucleases.  Deletions are rarely reversible. Substitutions, Insertions and Deletions

9  A point mutation is not a problem if it occurs in an intron section of DNA.  A point mutation may cause problems if it occurs in an exon region of DNA, since these areas of DNA code for protein. The effects of Point mutations on Protein

10  Insertion and Deletion mutations (but NOT substitution mutations) can result in frameshift mutations.  If a number of nucleotides is added or removed that is not a factor of 3 this causes the entire reading frame of the gene to be altered. Frameshift Mutation

11  Analogy:  THE CAT ATE THE RAT - delete C  THE ATA TET HER AT - no longer makes sense  THE CAT ATE THE RAT - add BAD  THE BAD CAT ATE THE RAT - still makes sense Frameshift Mutations


13  There are 3 main categories for how mutations affect the amino acid sequence of the protein: The effects of mutations on Protein

14 1) Silent Mutations  Due to the redundant nature of the genetic code the mutation codes for the same amino acid

15 2) Missense mutations  the mutation codes for a different amino acid

16  Can be harmful, for example alkaptonuria- most often due to a substitution mutation leading to a missense mutation.  Alters the gene for the enzyme that degrades tyrosine ;  Due to the faulty enzyme, homogentisic acid accumulates in the body, causes black urine damages cartilage &heart valves, causes kidney stones Missense Mutation Examples

17  Sickle Cell Anemia is another disease caused by a single base pair substitution leading to a missense mutation. Missense Mutation Examples

18  Missense Mutations can also be beneficial and may play a role in creating new proteins, such as antibodies, for fighting new infections. Missense Mutation Examples

19 3) Nonsense Mutations  the change results in a premature stop codon.

20  Can be lethal to the cell, usually very harmful to the organism. Nonsense Mutations

21  Change to the chromosome number is always detrimental, if not lethal, to the organism Chromosomal Mutations

22  Mutations can also involve rearrangement of genetic material which may affect several genes and several chromosomes and therefore protein synthesis.

23 Chromosomal Deletions and Duplications  Deletions result in a loss of genes  Duplications result in multiple copies of genes or even chromosomes.

24 Inversions  An inversion is the reversal of a segment of DNA in a chromosome.

25 Translocations  A translocation is the trading of chromosomal segments between two different chromosomes.

26 Translocations  They are usually not the same size segment being traded.  Some forms of cancer are caused by translocations (i.e. leukemia).

27  Spontaneous mutations occur naturally  Induced mutations are caused by environmental factors.  Causes of Spontaneous mutations include:  Errors in DNA replication  DNA transposition CAUSES OF MUTATIONS

28  movement of specific DNA sequences, called transposable elements, or transposons, within and between chromosomes.  Described by Barbara McClintock (American geneticist) DNA Transposition

29  A mutagen or mutagenic agent is a substance or event that increases the rate of mutation. Causes of Induced mutations

30  cause physical damage to DNA  X-Rays – point mutations and chromosomal deletions  UV radiation – causes reactions between adjacent pyrimidine bases (C and T) Physical Mutagens

31  Chemical mutagens react chemically with DNA to cause a nucleotide substitution or frameshift mutation.  May also have a similar structure to a nucleotide but with different base pairing properties Chemical Mutagens

32  Nitrites (small amounts in cured meats)  Gasoline fumes  50+ compounds found in cigarette smoke  Most chemical mutagens are also carcinogenic Examples of Chemical Mutagens

33  Mutations that accumulate too rapidly or are very harmful do not provide a selective advantage.  The DNA polymerase enzymes can repair errors made in DNA replication. DNA Repair

34  Mismatch repair by Mut proteins also helps to reduced replication errors.  Cells have other mechanisms that recognize and repair DNA that becomes damaged. DNA Repair

35  Photorepair is used to correct UV radiation damage. A photolyase enzyme uses visible light to cleave the bond made between adjacent pyrimidines.  Excision repair enzymes recognize and remove many different forms of damage, a DNA polymerase enzymes rebuild the removed segment. Examples of DNA Repair

36  Mutations are usually _______________and have no effect on the organism.  However, when mutations are _____________, they can have lethal effects.  _____________ mutations are rare and result in ____________________. Conclusion

37  _______________________affect one nucleotide  _______________________are caused by insertions or deletions of nucleotides.  The result of a mutation on the protein is considered __________ (no effect), _____________ (single amino acid change) or ______________ (premature stop codon). Conclusion

38  Chromosomes can have _______________, ___________________, _______________, and ___________________… all of which affect protein production and can lead to genetic disorders.  Stay away from _____________________as much as possible if you want to minimize your chances of accumulating mutations. Conclusion

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