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NCEA Level 3 Biology
MUTATIONS
Question 1: Mutations
a) Define the term mutation.
b) Many chemicals can act as mutagenic agents. Name TWO mutagenic agents that are not chemicals.
c) Explain where in the human body a mutation must take place in order for it to be inherited.
d) What is the name given to an organism with characteristics changed by a mutation?
e) Identify the type of gene mutation described in each case below.
GGTACG

GGCACG
ii) CAGTGT

CAGGTT
iii) ACTTCA

ACTTTCA
i)
f)
Another type of mutation is chromosomal mutations which can result in changes to the original sequence
of genes on the chromosome. The letters on the diagram below represent the positions of genes along a
chromosome.
a
b
c
d
e
f
Redraw this chromosome diagram to show the result of each of the following chromosomal mutations:
i) duplication
ii) inversion
g) Use your knowledge of the possible effects of gene mutations and how genes work to explain how a
mutated gene is more likely to be harmful to an individual than the normal gene.
h) Discuss (giving at least 3 reasons) why a point or gene mutation is less likely to have a major impact on
the phenotype of an organism compared with a chromosomal mutation.
i)
Give two reasons why a species is often protected against the inheritance of severe mutations carried by
individual organisms.
Evolutionists argue that “mutation is the key to genetic change and hence evolution”.
j)
Discuss (with arguments for and against) the idea that mutation provides sufficient change to produce new
species.
Question 2: Downs Syndrome
Down Syndrome is a condition caused by a chromosomal abnormality. Affected individuals are generally
trisomic for chromosome 21. This is an example of aneuploidy.
a) What is a syndrome?
b) What is the total chromosome number of a trisomic Downs Syndrome individual?
c) Explain what causes aneuploidy?
d) Suggest a possible reason why the presence of an extra chromosome causes such a profound effect on
the development of a person’s phenotype
(Please Turn Over)
Downs syndrome is about 100 times more likely to occur in children of mothers over 45, than in those of
mothers less than 19 years old. The age of the father on the other hand has a much less marked effect.
e) Discuss the reasons that this 'Maternal Age Effect' occurs and the reasons that there is no corresponding
'Paternal Age Effect'?
Question 3: Kiwifruit Polyploidy
Modern kiwifruit (Actinidia deliciosa var deliciosa) is a hexaploid (6N) and has probably evolved as a result of
polyploidy. Two other species of Actinidia are thought to have hybridised as part of the evolution of the modern
kiwifruit.
a) Define polyploidy.
A possible ancestry of the evolution of modern kiwifruit is shown below:
Actinidia species 1.
X
Actinidia species 2.
genome AA
genome BB
2N = 58
2N = 58
Actinidia chinensis.
new species
X
Actinidia species 3.
genome (i)
genome CC
4N = 116
2N = 58
Actinidia deliciosa
Modern kiwifruit
genome AABBCC
6N = (ii)
b) Complete the 2 boxes marked (i) and (ii) above.
c) Describe two ways in which polyploidy can be of use to plant breeders
Polyploidy in plants often results in the instant formation of a new species.
d) Discuss a possible sequence of events that could produce a new plant species from a single polyploid plant.
Question 4: Metabolic Disorders
a) Name a genetic metabolic defect which occurs as the result of a mutation affecting the breakdown
of the essential amino acid, phenylalanine.
b) Where in the metabolic pathway does this error occur?
c) What effect does this mutation have?
MARKING SCHEDULE
Question 1 Mutations
Question
1a
1b
1c
1d
1e
1f
1g
1h
1i
Evidence for
Achieved
A change in the DNA sequence
that is not repaired.
correct
- viruses
- high temperatures
- various high energy radiations
any 2.
In the ovaries or testes / gonads
Mutant
Correct
i. substitution
ii. inversion
iii. addition / insertion
need all 3
i. any duplication single gene or
more eg. abcddef, abcdbcdef.
ii. any inversion of 2 or more
genes eg abdcef, aedcbf.
Not fedcba.
need both
If it does not code for the
correct protein will there be an
effect / process cease /
structure not form.
correct idea
At least ONE valid reason given
for gene mutations and
chromosomal mutations
eg.
gene mutations:
- codon redundancy means
correct protein still produced
- protein may still function with
different amino acid especially
near end of an amino acid chain
- mutation may be recessive /
hidden in heterozygous state
- mutation may be repaired
- mutation in intron will not be
expressed.
chromosomal mutations
- usually more than 1 gene
affected
- can disrupt (regulator,
operator) control genes.
- there is no repair mechanism
Evidence for Achieved with
Merit.
Gene mutation may not change
the protein or may not change it
significantly.
Only if it does not code for the
correct protein will there be an
effect / process cease /
structure not form.
Both ideas
At least TWO valid reasons
given for gene mutations or
chromosomal mutations
eg.
gene mutations:
- codon redundancy means
correct protein still produced
- protein may still function with
different amino acid especially
near end of an amino acid chain
- mutation may be recessive /
hidden in heterozygous state
- mutation may be repaired
- mutation in intron will not be
expressed.
chromosomal mutations
- usually more than 1 gene
affected
- can disrupt (regulator,
operator) control genes.
- there is no repair mechanism
any 2 correct reasons eg.
- carriers die before breeding
- carriers rendered sterile
- natural selection eliminates
carriers (lower selective
advantage)
- mutation may be somatic / not
inheritable.
Evidence for Achieved with
Excellence.
3 or more valid reasons for
both gene mutations and
chromosome mutations
(comparisons made)
Has presented two arguments
for OR two arguments against
For
- mutations are the only way
genes can change / mutation is
the ultimate source of variation
- mutations are inheritable /
accumulated mutations can be
passed to next generation.
- mutations occur at a slow
steady rate that allows
evolutionary processes to select
for advantageous ones
Against
- mutations are usually harmful /
not expressed / need to be
homozygous (inherited from
both parents) to be expressed
- mutations can have multiple
phenotypic effect
- many mutations are corrected
- rate is low
- mutations on their own are not
sufficiently rapid, evolution
relies on independent
assortment and crossing-over to
provide new combinations
1j
2a
2b
2c
2d
2e
Need 2 arguments for AND 2
against.
Single cause (in this case an
extra chromosome) that has
multiple effects (physical and
intellectual)
correct idea.
47
correct answer
Non-disjunction (or
description) resulting in
gamete with 24 (extra)
chromosome
correct idea
Having an extra chromosome
may allow for the overproduction of some proteins
(An extra gene may cause
more mRNA to be produced.)
Gamete production in either
males or females is explained
Female: ova are present at birth
suspended (in prophase I) and
by the end of her reproductive
life the ova are old / spindle is
older and chance of nonseparation of chromosome pairs
is more likely
Males: sperm are produced
throughout reproductive life. not
suspended in prophase I
and/ or small paternal effect
possibly caused by factors such
as frequency of intercourse etc.
Comparison between gamete
production in males and
females needed.
3a
3b
3c
Contains more than 2 sets of
chromosomes / more than twice
the haploid number / process
that increases number of sets of
chromosomes
correct definition.
i. = AABB
ii.= 174
Both need to be correct
Larger plants / improved
disease resistance / seedless
plants can be developed /
enables new species to be
produced
Need to have two ideas
States one idea relating to
allopolyploidy or autopolyploidy
States two linked ideas relating
to allopolyploidy or
autopolyploidy
Need to link at least 3 ideas for
allopolyploidy OR
autopolyploidy
e.g. allopolyploidy
- sterile hybrid (result of
interbreeding), has incompatible
chromosome compliment
(AABB)
- can no longer interbreed with
original population.
- non-disjunction / doubling of
chromosome number restores
compatible (homologous) pairs
and plant becomes fertile
OR
e.g. Autopolyploidy
- Normal 2n plant (AA) also has
doubling of chromosome
number ( 4N = AAAA)
- chromosomes remain
compatible due to ability to pair
at meiosis.
then
- polyploid plant reproduces,
(initial single plant by asexual
means or self-fertilisation).
8
4
3d
4a
4b
4c
Phenylketonuria
It is caused by a defect in the
enzyme (phenylalanine
hydroxylase) that
converts phenylalanine to
tyrosine
Needs to describe specific
reaction
Causes an accumulation of
phenylalanine some of which is
converted into phenylpyruvic
acid. This two substances are
toxic and can cause mental
retardation
Total.
17
Total Sufficiency:
Achievement: 9A
Merit:
9A + 5M
Excellence: 9A + 5M + 3E