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Summary Grade 12 Biology: Mutations R50,00
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Summary Grade 12 Biology: Mutations

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A brief summary of mutations. these notes include definitions, a summary of genetic aberrations, the application of DNA technology and DNA profiling.

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  • May 20, 2020
  • 2
  • 2019/2020
  • Summary

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MUTATIONS
Genetic aberrations: caused by mutations
Mutations: any alteration in the genetic makeup (genetic code) of an organism

Genetic Aberrations
Factors that lead to genetic changes (changes in the sequence of nucleotides):
1. One or more nucleotides being damaged or lost by chance:
 Crossing over – paternal & maternal chromosomes in meiosis
 Replication of DNA
 Transcription – DNA to RNA
2. Breakdown of DNA by mutagens:
 Environmental factors – sunlight, radiation & smoking
 Mutagenic chemicals
 Viruses and micro-organisms
Mutagen: physical or chemical agents that induce and speed up mutations in DNA
Gene mutations: small, localised changes in the structure of DNA strands
Point mutations may occur by:
 Substitution – where one nucleotide is exchanged for another
 Insertions – where one or more extra nucleotides are added to the DNA molecule
 Deletions – where one or more nucleotides are removed from the DNA molecule
Point mutations: changes that involve a single nucleotide
 When the sequence of nucleotides is altered, individual codons are affected, altering the
mRNA transcribed from the mutated DNA. This causes the absence of, or incorrect form
of the protein for which that gene codes.

Application of DNA Technology
DNA profiling/fingerprinting:
 Involves extracting and identifying the highly variable regions of a person’s DNA that
contain STRs
STR (Short Tandem Repeat): repeating sequences of base
pairs
 At the same point in the DNA of different people, the
number of repeated sequences of base pairs varies
considerably
 Scientists can use samples from blood, bone, hair and other body tissues to generate a
DNA profile using the repeated sequences.

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