HSCBiology

Inquiry Question 1: How does mutation introduce new alleles into a population?

Content Descriptor: Explain how a range of mutagens operate, including but not limited to:

Electromagnetic radiation sources (6.1.1)

Physical (electromagnetic radiation sources)

• Ionising – Radioactive material which is highly ionising such as radioactive waste, causesbackbone or pairs to break
• UV radiation –Some UV can disrupt bonding or cause the formation of a thymine 
• Excessiveheat – Vibrate and break apart

Chemicals (6.1.2)

Chemical (may be base analogues fit into the place of a base, or intercalating agents which stick in between bases)

• Ingested –Tar, alcohol and fatty foods, adds bulky chemicals which interfere with 
• Irritantsand poisons – Benzene and cleaning products
• Metal pollutants – Mercury, arsenic, cadmium causes the formation of reactive oxygen

Naturally occurring mutagens (6.1.3)

Biological (naturally occurring mutagens)

• Transposons– Autonomous relocation and gene disruption
• Viruses– Change gene function, cause damage through 

Content Descriptor: Compare the causes, processes and effects of different types of mutation, 

including but not limited to:

Point mutation (6.1.4)

Point mutations refer to mutations to a single nucleic base pair.

• Substitution – Single base pairs are mutated into a different pair. When this occurs in all cellsin the individual, it is referred to as a SNPS. These can occur during DNA replication, due to a mutagen or a copying error. Usually has a low impact upon the individual, as it will only affect a single amino acid. Example diseases caused by substitution includes sickle cell 
• Deletion or insertion (frameshift) – The addition or removal of a single nucleic base pair. Thiscan be caused by intercalating mutagens. Shifts the codon reading frame to vastly alter phenotypic  Examples of diseases caused by this includes cystic fibrosis.

Changes caused by a point mutation can be:

• Silent – Substitution caused no change to amino acid produced and thus has no phenotypic
• Missense – Mutation causes the incorrect amino acid to be produced and added to This will affect phenotypic expression as the incorrect protein will be produced which will alter the cells’ physiology.
• Nonsense – Mutation prematurely places a stop codon, making the polypeptide undevelopedand non-functioning.

Chromosomal mutation (6.1.5)

Sectional changes:

Refers to a mutation of the sections of genes on the chromosomes. These mutations only occur during meiosis:

• Deletion – Segment of DNA is lost on chromosome. Will affect phenotypic expression sincegenetic information is not 
• Inversion – Section of DNA is inverted to be arranged in the opposite direction. Usually willnot have a large effect on genetic information since no genetic information is lost.
• Translocation – Sections of DNA are placed onto a different non-homologous chromosome.This will cause the gametes to either have more or less genetic 
• Duplication – Segment lost from one chromosome and added onto its’ homologous pair.Similar to translocation, this will cause the gametes to either have more or less genetic 

Aneuploidy:

The condition of having more or fewer chromosomes than the standard number (2N+1, 2N+2,2N- 1…). This usually results from the non-disjunction of chromosomes during anaphase I or II during meiosis.

Down Syndrome (trisomy 21):

A form of polysomy (greater number of chromosomes than standard), caused by an additional chromosome 21. Down Syndrome can be caused by:

• Non-disjunction of chromosome 21 in meiosis. This accounts for 95% of Down Syndrome
• Translocation of chromosome 21, attaching itself to another chromosome, usuallychromosome  This accounts for 3% of cases.
• Mioticerrors – The failure of the pair of chromosomes 21 to separate during early embryonic miotic  This accounts for under 3% of cases.

Down Syndrome occurs in approximately 1/800 births of women aged 30-31, increasing drastically as the maternal age increases, due to the high rate of mutation in eggs.

Characteristics of Down Syndrome include:

• Intellectualdisability
• Characteristicphysical features such as poor muscle tone
• Difficultywith speech and communication

Content Descriptor: Distinguish between somatic mutations and germ-line mutations and their effect on an organism: (6.1.6)

Germline:

• Occur in sex cells or the production organs for sex cells, caused by the exposure of these cellsto 
• Willbe passed onto offspring who receive mutated 
• Willaffect localised cells but may also impact a community through 

Somatic:

• Occur in a regular body cell. Caused by exposure to a mutagen, this mutation will beexpressed in any cells which are produced via mitosis as clones of the affected cell. Uncontrolled replication of cells affected by somatic mutations are 
• Cannotbe passed onto 
• Effect will be localised, impacting the functioning of the cells affected and possibly theindividual if the mutation is 

Cancer:

Normal cells are programmed to die in a process called apoptosis, usually corresponding with the time that they have accumulated damage which prevents them from carrying out their normal function.

Cancer cells have mutated such that their regulatory genes have been switched off, allowing them to continue to replicate regardless of the damage they have accumulated.

Content Descriptor: Assess the significance of ‘coding’ and ‘non-coding’ DNA segments in the process of mutation: (6.1.7)

Coding:

Coding segments of DNA hold the information which is changed into amino acids and proteins through the process of transcription translation. Mutations in these coding regions will therefore affect the proteins produced if the mutation is nonsense of missense. This will thus be phenotypically expressed through affecting cell processes and function.

Non-coding:

While non-coding sections do not code for proteins, mutations in these non-coding regions have been shown to affect regulatory proteins and the expression of genes. Thus, non-coding regions will also indirectly be expressed.

Content Descriptor: Investigate the causes of genetic variation relation to the processes of fertilisation, meiosis and mutation: (6.1.8)

Mutation:

Alterations in the genetic code causes changes to the amino acids which they code for. This changes the amino acids produced, altering protein shape and therefore cell functioning. If this mutation is in gametic cells, it may be passed onto offspring causing new alleles and thus genetic variation from parents.

Meiosis:

Division into homologous pairs and crossing over re-arrange existing alleles into new combinations creating genetic variation.

Fertilisation:

the mechanism by which meiosis and mutation act. The uniting of gametes allows for the new assembly of alleles producing genetic variation. Mate selection can also impact which genes are selected to be passed on.

Content Descriptor: Evaluate the effect of mutation, gene flow and genetic drift on the gene pool of populations: (6.1.9)

Effect on gene pool:

• Mutation – Acts via the mechanism of natural selection. Provides random mutations whichmay be beneficial to the survival of the organism making it more likely to be passed onto  Increases genetic diversity.
• Gene flow – Migration from one place to another, causes an increase or decrease in geneticdiversity due to the loss or gain of different allele frequencies. For example, sickle cell has a frequency of 0.1 in Sudan but a 0.01 frequency in Australia. A large migration from Sudan to Australia would alter the gene pool by increasing the sickle cell gene 
• Genetic drift – Random events which cause an allele frequency. This may be due to a weatherevent such as storm (known as bottleneck) or a small sample of the population moves to a new area, not fully representing the old population (the founder effect). Genetic drift can cause alleles to become fixed (100% frequency) or lost (0%) frequency. Tends to reduce genetic 

Hardy Weinberg Equilibrium:

Where P and Q represent a dominant and recessive allele:

Inquiry Question Review: How does mutation introduce new alleles into a population? (6.1.10)

You should be able to:

• Describethe different types of mutagens and how the operate
• Understandthe process and effects of:
  • Germlinemutation
  • Somaticmutation
  • Mutationin coding and non-coding regions
  • Geneflow
  • Geneticdrift
• Comparechromosomal and point mutations