MUTATIONSSlide 2 Mutations

Slide 3 Examples of Mutations

Slide 4 How Mutations occur

Slide 5 The Benefit of Mutations

Slide 6 Rate of Incidence

Slide 7 Gene Mutations

Slide 8 Frame Shift

Slide 9 Deletion and Inversion

Slide 10 Translocation and Duplication

Slide 11 Whole Chromosome Mutations

Slides 12 & 13 Polyploidy

MUTATIONSMutations are caused by Mutagens.

Pathogens (Microbes and viruses)

Radiation (Nuclear and Solar)

Chemicals (smoking, herbicides, pollutants, diet, etc.)

A carcinogen is a cancer causing mutagen.

Mutations change the genetic information in a cell.

If the cell is somatic then part of the organism will be affected.

If the cell is a gamete then the entire offspring will be affected.

Normal red blood cell

“Sickle” cell

SOME MUTATION EXAMPLES

HOW MUTATIONS OCCUROne example of the process by which genetic information is changed:

UV Light

Thymine dimer

DNA of tumour suppressor

gene

Lab manual page 140-2

BENEFITMost mutations are harmful.

Beneficial ones tend to occur more often in organisms with short generation times.

Many may be silent – not observed – and may only be selected for or against at a later date.

Neutral mutations make no change at all.Example:

mRNA

Amino acids

Mutant DNA

mRNA

DNA

This is known as Degeneracy – where multiple triplets code for one Amino acid.

Genes mutate at known rates. This rate varies depending on the gene involved. Some genes have high spontaneous mutation rates.

Mutation rates for genes within a species are probably similar, but the viability of mutations varies greatly.

Mutant genes in the human population:

With approximately 30,000 genes in the human genome and two copies of each gene, each cell has a total of 60,000 genes.

In higher organisms, a mutation for a specific gene will occur in one gamete in 300,000.

Then one in five of us on average carries about 1 new mutant gene!

Rates of Mutation

60,000 ÷ 300,000 = 0.2 = 20%

Lab manual page 143

GENE MUTATIONSMutations that affect one gene arise from point mutations – a change in the nucleotides on a DNA strand.

Base mismatching

- Missense substitution – may change one Amino Acid

- Nonsense substitution

Mutated DNA creates a STOP codon which prematurely ends synthesis of the polypeptide chain

Normal DNA

Mutant DNA

mRNA

Normal polypeptide

e.g. Sickle cell anaemia

Insertion

Deletion

Causes a frame shift – it stuffs up the whole rest of the sequence.

Large scale frame shift results in a new amino acid sequence. The resulting protein is unlikely to have any biological activity.

Mutation: Insertion of C

Original DNA

Mutant DNA

mRNA

Amino acids

Normal polypeptide

Lab manual page 145, 9

CHROMOSOME MUTATIONSThese can only occur during meiosis.

a.k.a. Block mutations.

Deletion: Inversion:

Examples:

Cru-Du-Chat, Prader-WilliExamples:

On chromosome 2 – unviable offspring

Translocation:

A section of one chromosome is lost to another one

Duplication:

A section of one chromosome is lost to its Homologue

Chromosomes 9 and 22 – chronic leukaemia

Chromosomes 9 – resulted in evolution of haemoglobin

Lab manual page 150-1

WHOLE CHROMOSOME MUTATIONSNormal (Euploid) humans have chromosomes (2 exact sets).

Aneuploidy is the term for having 1 or more missing or extra (not 2 sets).

Monosomy = only one of a pair

Polysomy = more than 2 of a pair, e.g. Trisomy = 3 homologues.

This normally results from non-disjunction during meiosis.

46

Somatic cell

Gametes

Some examples:

Trisomy chromosome 21 (Down’s)

Monosomy sex chromosome (XO = Turner’s)

Trisomy sex chromosome (XXY = Klinefelters)

Lab manual page 153-7

POLYPLOIDYn = haploid (gametes)

Usually only in plants.

Allopolyploidy – from mating between 2 species.

Autopolyploidy – from the same species.

Often the initial hybrid is sterile, but as it reproduces asexually non-disjunction (amphiploidy) causes a doubling of the chromosome number… resulting in a fertile species.

2n = diploid (normal individual)

3n or more = polyploidy

Autopolyploidy

Allopolyploidy

Lab manual page 158-9, (160-1)