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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