Biology Y11 2014 - DRM

MUTATIONSTypes of mutationsCauses ConsequencesExamples

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What is a mutation?

• A mutation is any change in the nucleotide sequence of an organism's DNA.

• It is an unpredictable, random change in the DNA. Mutations can take place in any type of cell: bacterial, fungal, plant, animal.

• Mutations are cumulative in a population. This leads to evolution (changes in time).

• Mutations can be neutral, beneficial or harmful.

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Types of mutations

• Affects one to three nucleotides

• Changes one gene• Point mutations are

changes in the genetic sequence that occur at a specific point along the DNA strand

MUTATIONS

point chromosomal

• Involve changes to large sections of a chromosome or affects even entire chromosomes

• Changes many genes

can be

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What causes mutations?

Changes in the DNA can be due to:

1. chance (spontaneous mutations)

2. mutagens.

Examples of mutagens are:• smoking • radiation (solar or nuclear)• toxic chemicals (pesticides, solvents)• high temperatures

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When and where• Mutations take place during DNA replication (making a

DNA copy) or during DNA transcription (copying the DNA to mRNA)

• Mutations can be located in germ cells or somatic cells. Somatic mutations take place in body cells. Germ-line mutations occur in gametes or in cells that eventually produce gametes. These mutations are passed on to an organism's offspring. As a result, future generations of organisms will carry the mutation in all of their cells.

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POINT MUTATIONS

There are several ways in which nucleotides can change:

• Insertion or Addition – adding an extra nucleotide

• Deletion – removing one nucleotide

• Substitution – changing one base for another

• Inversion – having the reversed order in a sequence

• Small number repeats – adding duplicates of very short sequences

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Examples of point mutations

Normal BEAST

substitution FEAST

Insertion BREAST

Inversion BEATS

Deletion BEST

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Consequences of point mutations

Mutations change transcription, therefore they affect the “reading frame”.

As a result, proteins may have different amino acids, or be terminated sooner.

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Consequences of base substitutions

Missense: the change in DNA sequence

changes the codon to a different amino acid.

If the amino acid is similar in structure, the mutation is silent or

neutral.

If the amino acid is different in structure,

the mutation leads to a altered protein. This

may lead to diseases.

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Consequences of base substitutions

Nonsense: a change

in the genetic code

results in the coding

for a stop codon rather

than an amino acid.

The shortened protein

is generally non-

functional or its

function is impeded.

This may lead to

diseases.

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Consequences of insertions or deletions

• Frameshift: The insertion or deletion of a number of bases that is not a multiple of 3. This alters the reading frame of the gene and frequently results in a premature stop codon and protein truncation.

Normal DNATHE BIG BAD FLY HAD ONE RED EYE AND ONE BLU EYE.

deletion in the 6th nucleotide:THE BIB ADF LYH ADO NER EDE YEA NDO NEB LUE YE.

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Examples of deletions

AUG AAA CUU CGC AGG AUG AUG AUG

AUG AAC UUC GCA GGA UGA UGA UG

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summary

Biology Y11 2014 - DRM

Sources

http://education-portal.com/academy/lesson/mutagens-and-the-eff ects-of-frameshift-mutations-definitions-and-examples.html#lesson

http://www.nature.com/scitable/topicpage/dna-is-constantly-changing-through-the-process-6524898

http://www.uvm.edu/~cgep/Education/Mutations.html

http://www.nature.com/scitable/topicpage/genetic-mutation-441