mutation

Question 1

Mutation

Answer 1

The alteration of a sequence of nucleotides in DNA, that may change the RNA product.

Question 2

Carcinogenic mutagens

Answer 2

Mutagens that change the cell cycle, causing increased cell division with no differentiation and creating masses of cells known as tumours.

Question 3

What mutations cause cancer?

Answer 3

Mutations in proto-oncogenes and tumour suppressor genes.

Question 4

Electromagnetic radiation sources

Answer 4

Enter cells from external sources and interfere with DNA molecules in the nucleus due to its highly-penetrative high-energy waves.

Ex. gamma rays, x-rays and UV light

Question 5

Pyrimidine dimers

Answer 5

UV creates a dimer structure by causing two adjacent base pairs to form covalent bonds with each other.

Question 6

Why are pyrimidine dimers bad?

Answer 6

They distort DNA’s double helix structure and prevent T bases form bonding with the opposite A bases.

The dimer structure isn’t replicated by DNA polymerase so no nucleotides are paired with the covalent pair, altering the mRNA sequence and negatively affecting protein structure/protein function.

Question 7

How else may radiation indirectly damage DNA?

Answer 7

By ionising other molecules to produce highly-reactive free radicals.

These unpaired electrons want to strip electrons from any molecules they encounter, reacting with DNA to damage it.

Question 8

Examples of chemical mutagens

Answer 8

Ingested chemicals like alcohol, charred and fatty foods. Environmental irritants and poisons like asbestos and pesticides.

Question 9

Base analogues

Answer 9

Chemicals structured similar to normal bases in DNA and may mistakenly become incorporated into DNA during replication. Results in mispairing of nucleotides, creating a non-functional protein product.

Question 10

Intercalating agents

Answer 10

Chemicals that insert themselves into the bonds between DNA pairs, altering the shape of DNA. Causes errors in replication.

Question 11

Reactive oxygen species

Answer 11

Chemicals that react directly with DNA and can cause breakages and cross-links in DNA strands.

Question 12

Naturally occurring mutagens

Answer 12

Spontaneous mutations like DNA replication errors that are retained because normal DNA repair doesn’t correct them

Question 13

Non biological naturally occurring mutagens

Answer 13

Metals like mercury and cadmium that occur naturally in the environment

Question 14

Biological naturally occurring mutagens

Answer 14

Viruses, bacteria, fungi and their products.

Mutagenic microbes can insert their own base sequence into DNA, changing the functioning of genes and triggering cancer.

Question 15

Transposons

Answer 15

Sections of DNA that spontaneously fragment and relocate or multiply within the genome.

When inserted into chromosomal DNA, they disrupt DNA functioning.

Question 16

Microbes

Answer 16

Mutagens such as viruses (HIV, hep B) and bacteria (Helicobacter) that may alter the genetic material in cells.

Question 17

Point mutation

Answer 17

A single nucleotide variation. Different from SNPs because they exist in less than 1% of the species’ population.

Question 18

Effects of point mutation

Answer 18

Affects phenotype if they occur within the exon of a gene, or affects gene expression when occurring within an intron.

Question 19

Base substitution

Answer 19

When one nucleotide base is replaces by a different base, possibly leading to a different amino acid inserted in the polypeptide.

Question 20

Nonsense mutation

Answer 20

Amino acid is changed into a premature stop codon, resulting in a non-functional resulting protein that has major phenotypic effect.

Question 21

Missense mutation

Answer 21

Results in an amino acid change. Functionality of the resulting protein is determined by whether the replacement amino acid is the same as the original.

Question 22

Silent mutation

Answer 22

When a substitution results in a new codon that still codes for the same amino acid, and thus have no effect on proteins and phenotype. Doesn’t alter amino acid sequence.

Question 23

Neutral mutation

Answer 23

Changes in DNA that result in an amino acid of the same type as the original so the change doesn’t significantly affect the structure of the protein.

Question 24

Sickle cell anaemia

Answer 24

A missense mutation; the amino acid glutamate is swapped for valine, altering the shape of the haemoglobin molecule and resulting in the sickle cell shape of the red blood cells.

Question 25

Insertions and deletions

Answer 25

The entire ‘reading frame’ of RNA is shifted, affecting every RNA codon after the change and impacting the production of the polypeptide. –> Frameshift mutation

Question 26

Effects of insertions or deletions

Answer 26

The polypeptide can be interrupted or not produced at all if one of the resulting codons is a stop codon. Ex. Muscular dystrophy

Question 27

Chromosomal mutation

Answer 27

Large-scale changes of DNA within a chromosome.

Question 28

Chromosomal deletion

Answer 28

When a section of DNA is removed and not replaced, leading to a reduction in the number of genes in a chromosome.

Question 29

Chromosomal insertion (duplication)

Answer 29

When a portion of DNA is duplicated and inserted. Effects depend on the size, location and number of repeats.

Question 30

Chromosomal inversion

Answer 30

When a section of DNA is removed, turned 180º and reinserted into the chromosome so that the bases are in reverse order. Ex. Haemophilia A, caused by an inversion mutation in the factor VII gene on the X chromosome.

Question 31

Chromosomal translocation

Answer 31

When a section of DNA is moved from one chromosome to a non-homologous chromosome. May lead to gene fusion, when the translocated region joins two normally separated genes.

Question 32

Aneuploidy

Answer 32

Numerical change in part of the chromosome set. Ex. Down syndrome

Question 33

Polyploidy

Answer 33

A numerical change in the whole set of chromosomes, resulting from all homologous chromosomes not separating during meiosis with one gamete having (2n) chromosomes and the others having none. Common in plants like tulips.

Question 34

Somatic mutations

Answer 34

Occurs in somatic cells (cells in the body other than sex organs), often due to replication errors prior to mitosis. Not hereditary, so no impact on species and their evolution. Ex. melanoma due to exposure to UV rays.

Question 35

How does a somatic mutation spread?

Answer 35

When a mutated cell continues to divide by mitosis, the error is replicated each time and passed onto cells in successive divisions, amplifying the error within that tissue. This may result in an observable phenotypic difference in the tissue such as cancer.

Question 36

Germline mutations

Answer 36

Occurs in the sexual reproductive cells that give rise to gametes and these mutations are passed to offspring. Can contribute to the species’ gene pool and influence whole populations of organisms and their evolution.

Question 37

How are germline mutations passed on?

Answer 37

When an affected gamete fuses with another and forms an embryo, the mutation is replicated in every cell of the embryo as it divides and grows, affecting all cells in the resulting child.

Question 38

Example of germline mutation in terms of meiosis

Answer 38

Homologous chromosomes in meiosis 1 or sister chromatids in meiosis 2 fail to separate correctly –> one gamete will end up with 2 copies of one chromosome, and another will end up without any copies of that chromosome.

Question 39

Coding DNA

Answer 39

Affects the type or sequence of amino acids in a protein end-product. As proteins are the product of genes in the coding region of DNA, if a mutation occurs, it directly affects the protein and the phenotype of the individual.

Question 40

How do coding DNA mutations affect eukaryotes?

Answer 40

May affect gene splicing and modify the function or levels of the protein product. The result of errors in eukaryotic genes involved in DNA repair are a general increase in mutations.

Question 41

How do coding DNA mutations affect prokaryotes?

Answer 41

Prokaryotic DNA is mostly coding DNA, so maintaining the integrity of DNA is essential for the survival of these species. Characteristics for DNA repair enzymes are not tolerant of genetic variation and change.

Question 42

Non-coding DNA

Answer 42

Mutations in these non-coding regions (regulatory sequences) affect gene expression and cell functioning.

Question 43

What is the significance of non-coding DNA in embryonic development?

Answer 43

Non-coding DNA is important during embryonic development, showing a link to birth defects. They may lead to developmental abnormalities that cause the embryo or foetus to be aborted, or may lead to congenital abnormalities.

Question 44

What evolutionary advantage is non-coding DNA suggested to provide?

Answer 44

Acts as a buffer area dividing one gene from the next. If a frameshift mutation arises, the introns will minimise the changes caused by the mutation. Gives leeway when genes break during crossing over, so the recombination doesn’t have to have pinpoint accuracy.