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BIOLOGY, M6 2025 HSC 12 MC

The following represents a karyotype for an individual with Down syndrome.

 

What conclusions can be drawn about the individual from this karyotype?

  1. A male with a deletion mutation
  2. A female with a deletion mutation
  3. A male with a chromosomal mutation
  4. A female with a chromosomal mutation
Show Answers Only

\(D\)

Show Worked Solution
  • D is correct: XX sex chromosomes indicate female; trisomy 21 is a chromosomal mutation.

Other Options:

  • A is incorrect: Down syndrome involves an extra chromosome, not a deletion.
  • B is incorrect: Down syndrome is caused by an extra chromosome 21, not deletion.
  • C is incorrect: The presence of two X chromosomes indicates a female individual.

BIOLOGY, M6 2024 HSC 3 MC

The image shows a chromosome that has undergone mutation. Each letter represents a gene.
 

What type of mutation has occurred?

  1. Deletion
  2. Duplication
  3. Inversion
  4. Substitution
Show Answers Only

\(B\)

Show Worked Solution
  • Looking at the sequence, we can see that genes C and E appear twice in the mutated chromosome (creating a repeat of genetic material).
  • This is characteristic of a duplication mutation rather than deletion (loss), inversion (reversal), or substitution (replacement).

\(\Rightarrow B\)

BIOLOGY, M6 2021 VCE 20 MC

The diagram below shows the chromosomes from two different but related plant species.
 

Compare the chromosomes of the two plant species.

The differences seen in the chromosomes of Plant species 2 compared to the chromosomes of Plant species 1 can be described as

  1. aneuploidy.
  2. polyploidy.
  3. triploidy.
  4. trisomy.
Show Answers Only

\(B\)

Show Worked Solution
  • Polyploidy – the cells of an organism have more than one pair of (homologous) chromosomes.

\(\Rightarrow B\)

BIOLOGY, M6 2023 HSC 20 MC

The diagram shows the karyotype of a normal female Tasmanian devil cell and the karyotype of a Tasmanian devil facial tumour cell.

M1, M2, M3 and M4 are marker chromosomes. These are chromosomes of unknown origin additional to the normal chromosomes found in the cells of Tasmanian devil facial tumour disease.

What can be deduced from the karyotypes?

  1. The karyotype of the tumour cells shows trisomy.
  2. The karyotype of tumour cells contains multiple chromosomal inversions.
  3. The karyotype of tumour cells contains both chromosomal insertions and deletions.
  4. The karyotype of the tumour cells contains more chromosomes than the karyotype of the normal Tasmanian devil cells.
Show Answers Only

\(C\)

Show Worked Solution
  • The karyotype of the tumour cells contains a deletion of the chromosome set 2 and addition of marker chromosomes.

\(\Rightarrow C\)

BIOLOGY, M6 EQ-Bank 27

Compare the processes and effects of point mutations and chromosomal mutations. Include examples in your answer.   (8 marks)

Show Answers Only
  • Mutations are the change in an individuals genome. Their effects are dependent on
    • the location of the mutation. Mutations in coding DNA can affect proteins and have adverse physiological affects while mutations in non-coding DNA often have no affect, however may slightly impact cell activity.
    • the type of cell it occurs in. Somatic cell mutations only affect the individual, while germ-line mutations occur in germ-line cells which go on to produce gametes, thus potentially affecting offspring. 
  • Point mutations are mutations which change only a single base in a DNA sequence. They can be a single base substitution or the deletion or insertion of an extra base. Deletion or insertions are referred to as ‘frameshift’ mutations as they impact all codons proceeding it.
  • Sometimes substitution mutations are neutral and occur in non-coding DNA, code for an amino acid of very similar chemical composition or even code for the same amino acid. When a mutation does code for a dissimilar amino acid or a stop codon causing premature termination, this interferes with the shape of the polypeptide chain and the protein it becomes part of, rendering it faulty or completely unusable (e.g. sickle cell anaemia, NRAS mutation). The nature of frameshift mutations affecting every codon proceeding it are often more severe, as there is more potential to cause a faulty polypeptide chain (e.g. cystic fibrosis).
  • Chromosomal mutations can refer to the removal, insertion, translocation or inversion of large sections of a chromosome. These often affect genes by either splitting them up or relocating them to a new chromosome.
  • Chromosomal mutations can also refer to the relocation of entire chromosomes during meiosis of germ-line cells where they fail to separate. This is called non-disjunction and results in aneuploidy of two gametes, one which will result in having an extra chromosome (trisomy) and one will lack a chromosome (monosomy). Conditions such as Down’s syndrome (trisomy-21) or Turner syndrome (XO) are aneuploidy conditions but most often cause a miscarriage or unsuccessful zygote development.
  • Polyploidy is the complete development of an entirely new set of chromosomes. This is known to occur in strawberries which have 8 sets of chromosomes but cannot occur in humans.
  • While both can cause radical health defects, it is important to note that these mutations are the basis of evolution. Beneficial mutations are more likely to be carried through a species through generations according to natural selection.
Show Worked Solution
  • Mutations are the change in an individuals genome. Their effects are dependent on
    • the location of the mutation. Mutations in coding DNA can affect proteins and have adverse physiological affects while mutations in non-coding DNA often have no affect, however may slightly impact cell activity.
    • the type of cell it occurs in. Somatic cell mutations only affect the individual, while germ-line mutations occur in germ-line cells which go on to produce gametes, thus potentially affecting offspring. 
  • Point mutations are mutations which change only a single base in a DNA sequence. They can be a single base substitution or the deletion or insertion of an extra base. Deletion or insertions are referred to as ‘frameshift’ mutations as they impact all codons proceeding it.
  • Sometimes substitution mutations are neutral and occur in non-coding DNA, code for an amino acid of very similar chemical composition or even code for the same amino acid. When a mutation does code for a dissimilar amino acid or a stop codon causing premature termination, this interferes with the shape of the polypeptide chain and the protein it becomes part of, rendering it faulty or completely unusable (e.g. sickle cell anaemia, NRAS mutation). The nature of frameshift mutations affecting every codon proceeding it are often more severe, as there is more potential to cause a faulty polypeptide chain (e.g. cystic fibrosis).
  • Chromosomal mutations can refer to the removal, insertion, translocation or inversion of large sections of a chromosome. These often affect genes by either splitting them up or relocating them to a new chromosome.
  • Chromosomal mutations can also refer to the relocation of entire chromosomes during meiosis of germ-line cells where they fail to separate. This is called non-disjunction and results in aneuploidy of two gametes, one which will result in having an extra chromosome (trisomy) and one will lack a chromosome (monosomy). Conditions such as Down’s syndrome (trisomy-21) or Turner syndrome (XO) are aneuploidy conditions but most often cause a miscarriage or unsuccessful zygote development.
  • Polyploidy is the complete development of an entirely new set of chromosomes. This is known to occur in strawberries which have 8 sets of chromosomes but cannot occur in humans.
  • While both can cause radical health defects, it is important to note that these mutations are the basis of evolution. Beneficial mutations are more likely to be carried through a species through generations according to natural selection.

BIOLOGY, M6 EQ-Bank 14 MC

Which of the following is true of a mutation that produces an allele that is dominant?

  1. It would be expected to cause death.
  2. It could give an observable phenotype in a heterozygous genotype.
  3. It could give an observable phenotype only in a homozygous genotype.
  4. It would be expected to spread more quickly through a population than a recessive mutation.
Show Answers Only

`B`

Show Worked Solution

By Elimination

  • Mutations are not expected to cause death as death is dependant on the location and type of mutation (Eliminate A).
  • A dominant allele mutation vs recessive has no impact on spread in a population (Eliminate D).
  • The change in phenotype is not only possible in homozygous recessive phenotypes but also in heterozygous individuals (Eliminate C).

`=>B`

BIOLOGY, M6 EQ-Bank 12 MC

The bread mould, Neurospora crassa, normally produces its own amino acids from raw materials through a system of enzymes.
 

If a mutation occurred in gene B, the bread mould would still produce arginine if supplied with

  1. citrulline.
  2. ornithine.
  3. enzyme C.
  4. raw materials.
Show Answers Only

`A`

Show Worked Solution
  • Enzyme B only aids the production of ornithine to citrulline.
  • If the mould was directly supplied with citrulline, this would bypass enzyme B and it would be able to still produce arginine.

`=>A`

BIOLOGY, M6 2019 HSC 25

A human karyotype that shows evidence of chromosomal mutation is shown.

  1. Identify the evidence of chromosomal mutation in the karyotype.  (1 mark)

  2. Explain how cell division and fertilisation could lead to the production of this karyotype.  (4 marks)

Show Answers Only

a.   There is only one copy of the sex chromosome (Monosomy, Turner Syndrome).

b.    Process of producing karyotype:

  • During meiosis to produce a gamete, homologous chromosomes (during meiosis I) or sister chromatids (during meiosis II) may fail to separate.
  • This can occur with sex chromosomes, producing one gamete with 2 copies of the sex chromosome, and one without.
  • When the gamete without any sex cells undergoes fertilisation with a normal gamete with only one sex cell, the zygote will have only one sex cell, like the karyotype above.
Show Worked Solution

a.   There is only one copy of the sex chromosome (Monosomy, Turner Syndrome).

b.    Process of producing karyotype:

  • During meiosis to produce a gamete, homologous chromosomes (during meiosis I) or sister chromatids (during meiosis II) may fail to separate.
  • This can occur with sex chromosomes, producing one gamete with 2 copies of the sex chromosome, and one without.
  • When the gamete without any sex cells undergoes fertilisation with a normal gamete with only one sex cell, the zygote will have only one sex cell, like the karyotype above.

♦ Mean mark (a) 47%
♦♦♦ Mean mark (b) 24%.

BIOLOGY, M8 2022 HSC 24

Birth defects in humans can be caused by chromosomal abnormalities.

\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\quad \textit{Maternal} \quad & \textit{Prevalence of}\\
\textit{age} & \textit{chromosomal}\\
\text{(years)} & \textit{abnormalities}\\
\text{} & \rule[-1ex]{0pt}{0pt}\text{(per 1000 births)}\\
\hline \rule{0pt}{2.5ex}20 \rule[-1ex]{0pt}{0pt}& 1.5 \\
\hline \rule{0pt}{2.5ex}30 \rule[-1ex]{0pt}{0pt}& 3 \\
\hline \rule{0pt}{2.5ex}35 \rule[-1ex]{0pt}{0pt}& 8 \\
\hline \rule{0pt}{2.5ex}40 \rule[-1ex]{0pt}{0pt}& 22 \\
\hline \rule{0pt}{2.5ex}45 \rule[-1ex]{0pt}{0pt}& 38 \\
\hline
\end{array}

  1. Draw a suitable graph of the data provided in the table. Include a suitable line of best fit.  (3 marks)
     

  1. Outline the trend shown in the data.  (2 marks)

  2. Explain the cause of a type of chromosomal mutation.  (3 marks)

Show Answers Only

a. 

 

b.   Data trend:

  • After 20 years of age, the older a woman is when she gives birth, the chance of her child having a chromosomal abnormality increases exponentially.

c.   Cause of chromosomal mutation:

  • Aneuploidy is a chromosomal mutation where the child contains either an extra or a deficit of a chromosome.
  • This is a result of non-disjunction, where in meiosis, chromosomes fail to separate.
  • This can produce a gamete with an extra chromosome (trisomy, 2N+1) or one missing a certain chromosome (monosomy, 2N-1).
  • Down Syndrome (Trisomy 21) is the result of a child containing an extra chromosome 21.

Other answers could include

  • Polyploidy, duplications of whole sets of chromosomes (XN).
  • Rearrangement, deletion, insertion, translocation or duplications of sections of a chromosome.
Show Worked Solution

a. 

b.   Data trend:

  • After 20 years of age, the older a woman is when she gives birth, the chance of her child having a chromosomal abnormality increases exponentially.

♦ Mean mark (a) 54%.
Mean mark (b) 56%.

c.   Cause of chromosomal mutation:

  • Aneuploidy is a chromosomal mutation where the child contains either an extra or a deficit of a chromosome.
  • This is a result of non-disjunction, where in meiosis, chromosomes fail to separate.
  • This can produce a gamete with an extra chromosome (trisomy, 2N+1) or one missing a certain chromosome (monosomy, 2N-1).
  • Down Syndrome (Trisomy 21) is the result of a child containing an extra chromosome 21.

Other answers could include

  • Polyploidy, duplications of whole sets of chromosomes (XN).
  • Rearrangement, deletion, insertion, translocation or duplications of sections of a chromosome.

♦♦ Mean mark (c) 32%.

BIOLOGY, M6 2020 HSC 23

The following diagram shows a mutation.
 

  1. What type of mutation is shown in the diagram?   (1 mark)

  2. Outline another type of mutation.   (2 marks)

Show Answers Only

a.   Point mutation (substitution of adenosine to thymine, base number 8).

b.   Chromosomal mutation:

  • This occurs when there is a change in the number or structure of chromosomes within an individual’s genome.
Show Worked Solution

a.   Point mutation (substitution of adenosine to thymine, base number 8).

b.   Chromosomal mutation:

  • This occurs when there is a change in the number or structure of chromosomes within an individual’s genome.

♦ Mean mark (b) 46%.

BIOLOGY, M6 2021 HSC 6 MC

A mutation involving a DNA deletion is illustrated.
 

Which statement about the mutation is correct?

  1. It will have an effect on many genes.
  2. It will have an effect on only one codon.
  3. It may be the result of an error during translation.
  4. It may be the result of an error during transcription.
Show Answers Only

`A`

Show Worked Solution
  • A single chromosome has thousands of genes.
  • Deleted area will have an effect on many genes.

`=>A`


♦ Mean mark 40%.