NESA Biology Mutation
15 sample questions with marking guides and sample answers · Avg. score: 72.3%
Ionising radiation like X-rays causes mutations by
inhibiting DNA polymerase activity.
promoting DNA base mispairing.
inserting extra nucleotides into a DNA strand.
causing breaks in DNA strands.
Reveal Answer
inhibiting DNA polymerase activity.
Ionising radiation damages the DNA structure directly rather than targeting or inhibiting the enzymes involved in DNA replication, such as DNA polymerase.
promoting DNA base mispairing.
While chemical mutagens or base analogs typically promote base mispairing, ionising radiation primarily causes severe structural damage to the DNA backbone.
inserting extra nucleotides into a DNA strand.
Intercalating agents (like ethidium bromide), not ionising radiation, cause mutations by inserting themselves between DNA bases, which can lead to the insertion or deletion of nucleotides.
causing breaks in DNA strands.
Ionising radiation, such as X-rays, carries enough high-energy to break the phosphodiester bonds in the DNA backbone, leading to single- or double-strand breaks that cause mutations.
If a geneticist is studying the amino acid sequence of haemoglobin, they are most likely looking for the possibility of
sickle cell anaemia or thalassemia.
Tay-Sachs disease or thalassemia.
thalassemia or malaria.
malaria or sickle cell anaemia.
Reveal Answer
sickle cell anaemia or thalassemia.
Both sickle cell anaemia and thalassemia are genetic disorders that directly affect the structure or production of haemoglobin chains, which can be identified by studying its amino acid sequence.
Tay-Sachs disease or thalassemia.
While thalassemia affects haemoglobin, Tay-Sachs disease is caused by a mutation affecting the enzyme beta-hexosaminidase A, which is unrelated to haemoglobin.
thalassemia or malaria.
Thalassemia is a genetic disorder affecting haemoglobin, but malaria is an infectious disease caused by a parasite, not a genetic mutation in the haemoglobin protein.
malaria or sickle cell anaemia.
Sickle cell anaemia is caused by a mutation in haemoglobin, but malaria is a parasitic infection, not a genetic disorder found in the amino acid sequence of haemoglobin.
A mutation is a permanent change in the DNA code. Lactase persistence is the ability to digest lactose (the sugar found in milk) in adults. This ability is attributed to a mutation that became present in various gene pools between 2000 and 20 000 years ago. Only about 35% of the world's adults possess the mutation today and can effectively digest lactose.
Identify and describe the type of mutation that would be responsible for lactase persistence, considering that it has been maintained within the gene pool. Compare this type of mutation to mutations that are not passed to future generations.
Reveal Answer
Germ-line mutation.
This type of mutation is not somatic, found in the gametes and not body cells. Germ-line mutation is involved with the formation of offspring, and is not removed from the gene pool when the individual dies
| Descriptor | Marks |
|---|---|
germ-line mutation | 1 |
not somatic | 1 |
found in the gametes not body cells | 1 |
involved with production of the zygote/formation of offspring | 1 |
not removed from the gene pool when the individual dies | 1 |
Point mutations can alter the DNA code in a number of ways, one of these being a frameshift mutation. Explain what a frameshift mutation is and describe two other ways point mutations can alter the DNA code.
Reveal Answer
A frameshift mutation occurs when nucleotides are added or removed from a section of code, which results in new codons.
Other types of mutations include silent mutations, where the codon still codes for the same amino acid, and can be caused by the insertion of a new nucleotide.
Missense mutations occur when the code is changed to a different amino acid, caused by the substitution of one nucleotide being replaced by a new nucleotide.
Frameshift
| Descriptor | Marks |
|---|---|
States that a frameshift occurs when nucleotides are added or removed from a section of code | 1 |
States that it results in new codons/codes for different amino acids | 1 |
Other types of mutations 1
Marking Bands| Descriptor | Marks |
|---|---|
Describes a mutation type (silent, missense, or nonsense) and its cause/effect | 2 |
Identifies a mutation type or describes its cause/effect only | 1 |
None of the above | 0 |
Other types of mutations 2
Marking Bands| Descriptor | Marks |
|---|---|
Describes a second mutation type (silent, missense, or nonsense) and its cause/effect | 2 |
Identifies a second mutation type or describes its cause/effect only | 1 |
None of the above | 0 |
In farming populations, the allele frequency for lactase persistence can be as high as 96% whereas in non-farming populations the frequency is only 20%. Explain how natural selection could be responsible for this difference in allele frequency.
Reveal Answer
Lactase persistence mutation became present, causing variation in the gene pool in populations that used milk as an energy source.
Those that had the lactase persistence mutation had a better chance of survival, somore individuals with the lactase persistence allele survive to reproduce. So more offspring is born with the mutation present. Thus, allele frequency of the mutation increases over time.
In populations without a milk diet there would be no difference in survival rate, so allele frequency of mutation remains unchanged
| Descriptor | Marks |
|---|---|
lactase persistence mutation became present | 1 |
causing variation in the gene pool | 1 |
in populations that used milk as an energy source | 1 |
those that had the lactase persistence mutation had a better chance of survival | 1 |
more individuals with the lactase persistence allele reach adulthood/survive to reproduce | 1 |
more offspring born with the mutation present | 1 |
allele frequency of the mutation increases over time | 1 |
in populations without a milk diet there would be no difference in survival rate/selection advantage | 1 |
allele frequency of mutation remains unchanged | 1 |
Use the following information to answer the question.
A scientist identified a single-stranded molecule with the structure shown below.
| exon | intron | exon | intron | exon | intron |
|---|---|---|---|---|---|
| 50 bases | 150 bases | 70 bases | 80 bases | 120 bases | 40 bases |
It would be reasonable for the scientist to conclude that this molecule is
mature mRNA.
pre-mRNA.
copy DNA.
DNA.
Reveal Answer
mature mRNA.
Mature mRNA has already undergone splicing to remove introns, so it would only contain exons.
pre-mRNA.
Pre-mRNA is a single-stranded transcript that contains both coding regions (exons) and non-coding regions (introns) before it is processed.
copy DNA.
Copy DNA (cDNA) is synthesized from mature mRNA using reverse transcriptase, meaning it lacks introns.
DNA.
While genomic DNA contains both exons and introns, it is typically a double-stranded molecule, whereas the molecule described is single-stranded.
Random assortment of chromosomes occurs during
fertilisation.
meiosis I.
meiosis II.
mitosis.
Reveal Answer
fertilisation.
Incorrect. Fertilisation involves the random fusion of two haploid gametes to form a diploid zygote, rather than the random assortment of chromosomes during cell division.
meiosis I.
Correct. Random (independent) assortment occurs during metaphase I of meiosis I, when homologous chromosome pairs align randomly at the cell equator before separating into daughter cells.
meiosis II.
Incorrect. Meiosis II involves the separation of sister chromatids, not the random assortment of homologous chromosome pairs, which already took place during meiosis I.
mitosis.
Incorrect. Mitosis produces genetically identical daughter cells and does not involve the pairing or random assortment of homologous chromosomes.
Which of the following are all selection pressures which could reduce genetic variation in a population?
disease, increased competition and climate change
increased food availability, disease and climate change
increased competition, reduced environmental pollutants and disease
reduced land availability, increased food availability and climate change
Reveal Answer
disease, increased competition and climate change
Disease, increased competition, and climate change are all strong selection pressures that can cause significant mortality, eliminating disadvantageous alleles and reducing overall genetic variation.
increased food availability, disease and climate change
Increased food availability is a relaxed selection pressure that reduces competition, allowing more individuals to survive and typically maintaining or increasing genetic variation.
increased competition, reduced environmental pollutants and disease
Reduced environmental pollutants represents a relaxation of selection pressure, which allows a wider variety of phenotypes to survive rather than reducing genetic variation.
reduced land availability, increased food availability and climate change
Increased food availability relaxes selection pressure, meaning more individuals with diverse traits can survive, which does not reduce genetic variation.
Species of the genus Homo do not possess the powerful jaw muscles commonly found in the genera Australopithecus and Paranthropus. According to the fossil record, this decrease in the size of jaw muscles coincided with changes in brain size. Scientists have discovered that both the reduction in the size of the jaw muscles and the change in brain size occurred due to mutations.
Describe the various types of mutations, identify the causes and describe how they can occur.
Reveal Answer
A mutation is a change in a gene or a chromosome, leading to new characteristics in an organism or their offspring.
Mutations can be gene mutations or chromosomal mutations. Gene mutations are changes in a single gene which occur during DNA replication, while chromosomal mutations affect all or part of a chromosome. Mutations can also be somatic or germline. Somatic mutations occur in the body cells, meaning reproductive cells are not affected and therefore the mutation is not passed on to offspring. Germline mutations occur in the reproductive cells or gametes, and therefore can be passed on to offspring.
Mutations can be caused by mutagenic agents, which are substances that are known to increase the rate at which mutations occur, such as ionising radiation (e.g. X-rays), mustard gas, formaldehyde, and some antibiotics. Mutations can also be caused by errors in DNA replication, resulting in deletion where part of a chromosome is lost, duplication where a section of chromosome is repeated or occurs twice, etc. Finally, mutations can be caused by errors in cell division, leading to inversion where a broken part of a chromosome joins back but in the wrong way, translocation where part of a chromosome breaks off and re-joins to the wrong chromosome, etc.
Define
| Descriptor | Marks |
|---|---|
Defines a mutation as a change in a gene or a chromosome (leading to new characteristics in an organism or their offspring) | 1 |
Types of mutations
| Descriptor | Marks |
|---|---|
1 mark for each valid point (up to 3 marks):
| 3 |
1 mark for each valid point (up to 3 marks):
| 3 |
Causes - Mutagens
| Descriptor | Marks |
|---|---|
States mutations are caused by mutagens/mutagenic agents | 1 |
Defines mutagens as substances that are known to increase the rate at which mutations occur (e.g. ionising radiation, mustard gas, formaldehyde, some antibiotics) | 1 |
Causes - DNA replication
| Descriptor | Marks |
|---|---|
States mutations are caused by errors in DNA replication | 1 |
1 mark for each valid point (up to 2 marks): Deletion: part of a chromosome is lost; Duplication: section of chromosome is repeated/occurs twice; Insertions: DNA can be duplicated/extra DNA added; Frameshifts: incomplete DNA code/unreadable DNA code | 2 |
Causes - Cell division
| Descriptor | Marks |
|---|---|
States mutations are caused by errors in cell division/meiosis | 1 |
1 mark for each valid point (up to 2 marks): Inversion: broken part of chromosome joins back but in the wrong way; Translocation: part of chromosome breaks off and re-joins to the wrong chromosome; Non-disjunction: during meiosis, a chromosome pair does not separate so one daughter cell has an extra chromosome and one daughter cell has one less (aneuploidy) | 2 |
Explain how the example of the evolution of the unique hominin jaw illustrates the importance of mutations to evolution.
Reveal Answer
Mutations introduce new alleles into a population. Hominin jaw mutations must have been an advantage to survival, as the organisms are better suited to bipedal locomotion. These favourable alleles are passed onto offspring, meaning the mutation is maintained in future generations.
| Descriptor | Marks |
|---|---|
Award 1 mark for each of the following points, up to a maximum of 5 marks:
| 5 |
An error during DNA replication resulted in the following change to mRNA transcripts.
| mRNA before | AUGAAGUUUGGCAUC ... (continued) |
| mRNA after | AUGAAGUUUGCAUCG ... (continued) |
The DNA replication error most likely involved
deletion of cytosine.
insertion of guanine.
substitution of uracil with guanine.
substitution of guanine with cytosine.
Reveal Answer
deletion of cytosine.
Comparing the sequences reveals that a guanine (G) is missing in the "after" mRNA (changing ...GGC... to ...GCA...), which causes a frameshift. Since mRNA guanine is transcribed from cytosine on the DNA template strand, a deletion of cytosine in the DNA would result in this specific error.
insertion of guanine.
An insertion would add a base to the sequence. The comparison shows that a nucleotide has been removed (deleted) rather than added, as the sequence has shifted to the left.
substitution of uracil with guanine.
A substitution replaces one nucleotide with another without changing the length of the sequence. The observed change is a frameshift mutation caused by a deletion, which alters the reading frame of all subsequent codons.
substitution of guanine with cytosine.
This describes a substitution mutation. However, the sequences show that a base was removed entirely, causing the downstream sequence to shift, which characterizes a deletion mutation rather than a substitution.
Outline how ONE type of electromagnetic radiation can cause a germline mutation.
Reveal Answer
X-rays are a type of electromagnetic radiation that damages the structure of DNA. If this damage occurs to the DNA in gametes (sex cells) then it is a germline mutation.
| Descriptor | Marks |
|---|---|
Outlines how a named type of electromagnetic radiation can cause a DNA mutation | 2 |
Provides some relevant information | 1 |
None of the above | 0 |
Explain the difference between exons and introns.
Reveal Answer
Exons are sequences of coding DNA, which is transcribed into mRNA and then translated into proteins.
Introns are sequences of non-coding DNA and have a variety of other functions. They are spliced out of the mRNA prior to translation.
| Descriptor | Marks |
|---|---|
States that exons are coding DNA and introns are non-coding DNA | 1 |
Explains that exons are transcribed into mRNA and then translated into proteins, whereas introns are spliced out of mRNA and have other functions | 1 |
State a function of telomeres.
Reveal Answer
Telomeres protect the ends of chromosomes from being degraded, prolonging their life.
| Descriptor | Marks |
|---|---|
States a function of telomeres | 1 |
Mutation is the ultimate source of genetic variation because mutation
results from errors in DNA replication.
can be caused by environmental factors.
can create new alleles.
changes allele frequencies.
Reveal Answer
results from errors in DNA replication.
While mutations often result from DNA replication errors, this describes the mechanism of how mutations occur, not why they are the ultimate source of genetic variation.
can be caused by environmental factors.
Environmental factors like radiation or chemicals can cause mutations, but this explains the origin of mutations rather than their fundamental role in generating genetic variation.
can create new alleles.
Mutation is the only evolutionary mechanism that can generate entirely new alleles (DNA sequences), providing the raw material for genetic variation and evolution.
changes allele frequencies.
While mutation can change allele frequencies, other mechanisms like natural selection, gene flow, and genetic drift also do this. Mutation is unique because it creates new genetic material.
Koalas were once widespread in Australia. Due to a variety of factors, their population decreased and fragmented into small pockets, forcing them to inbreed. They have recently been hit by devastating epidemic diseases.
Explain why koalas face an increased extinction risk from disease.
Reveal Answer
High genetic diversity may allow for some members of the population to survive diseases and later reproduce and pass on their resistance to increase the survivability of the population.
However, inbreeding creates low genetic diversity, which makes koalas vulnerable to extinction due to disease.
| Descriptor | Marks |
|---|---|
Explains how genetic diversity can prevent extinction during rapid environmental change, e.g. disease | 1 |
Describes why koalas have low genetic diversity (inbreeding) | 1 |
States that koalas are more vulnerable to extinction due to low genetic diversity | 1 |
Which of the following is a type of physical mutagen?
alkylating agent
base analogue
UV light
transposable element
Reveal Answer
alkylating agent
Incorrect. Alkylating agents are chemical mutagens, not physical ones, because they induce mutations by chemically adding alkyl groups to DNA bases.
base analogue
Incorrect. Base analogues are chemical mutagens that structurally resemble normal DNA bases and cause errors when mistakenly incorporated during DNA replication.
UV light
Correct. Ultraviolet (UV) light is a physical mutagen (a form of radiation) that physically damages DNA by causing the formation of pyrimidine dimers.
transposable element
Incorrect. Transposable elements are biological mutagens, or mobile genetic elements, that cause mutations by inserting themselves into different locations within the genome.
Which event could cause a frameshift mutation?
non-disjunction during meiosis
error during replication
base pair substitution
heat damage
Reveal Answer
non-disjunction during meiosis
Non-disjunction involves the failure of chromosomes to separate during meiosis, leading to an abnormal number of chromosomes (aneuploidy) rather than a mutation within the DNA sequence.
error during replication
Frameshift mutations are caused by the insertion or deletion of nucleotides that are not multiples of three; these errors frequently occur due to strand slippage during DNA replication.
base pair substitution
Base pair substitution involves replacing one nucleotide with another (point mutation), which affects a single codon but does not shift the reading frame of the entire gene.
heat damage
Heat damage typically causes chemical changes like deamination or depurination, which usually result in base substitutions (point mutations) rather than the insertions or deletions required for a frameshift.
A dog has an extra chromosome in all its cells. The mutation that caused this most likely occurred in a
cell undergoing meiosis in the dog.
cell undergoing mitosis in the dog.
germ cell in one of the dog's parents.
somatic cell in one of the dog's parents.
Reveal Answer
cell undergoing meiosis in the dog.
A mutation occurring during meiosis in the dog would affect its gametes and potential offspring, not the dog's own body cells.
cell undergoing mitosis in the dog.
A mutation during mitosis in the dog would only affect the specific lineage of cells descended from that mutated cell, resulting in a mosaic rather than affecting all cells.
germ cell in one of the dog's parents.
For every cell in the dog's body to have an extra chromosome, the nondisjunction event must have occurred in a parent's germ cell, creating a gamete that passed the extra chromosome to the initial zygote.
somatic cell in one of the dog's parents.
Mutations in a parent's somatic (body) cells are not passed down to their offspring; only mutations in germ cells are inherited.