Mutation

• Mutations can lead to new alleles being formed, and this caused genetic diversity.
• Not all mutations do lead to new alleles though.
• Point Mutations - change only one triplet by substituting one nucleotide for a different one.
• There are three types of point mutations: silent, nonsense, and missense.
• What are the three types of point mutations?

  -Silent

  -Nonsense

  -Missense
• Silent Mutation - When a base is changed, but the amino acid does not change as the genetic code is degenerate.
• Nonsense Mutation - When the base change causes the amino acid to be swapped for a stop codon, resulting in a truncated protein, as translation will be terminated early.
• Missense Mutation - A point mutation which causes a change in amino acid structure, changing the protein's primary and tertiary structure.
• What is a silent mutation?

  When a base is changed, but the amino acid does not change as the genetic code is degenerate.
• What is a nonsense mutation?

  When the base change causes the amino acid to be swapped for a stop codon, resulting in a truncated protein, as translation will be terminated early.
• What is a missense mutation?


  A point mutation which causes a change in amino acid structure, changing the protein's primary and tertiary structure.
• The genetic code is universal ----> the same codon/triplets always code for the same amino acid in all organisms.
• The genetic cod is non-overlapping ----> each base/triplet/codon is only read once.
• The genetic code is degenerate ----> more than one triplet/codon can code for the same amino acid.
• What is meant by the genetic code being universal?

  The same codon/triplets always code for the same amino acid in all organisms.
• What is meant by the genetic code being non-overlapping?

  Each base/triplet/codon is only read once.
• What is meant by the genetic code being degenerate?

  More than one codon/triplet can code for the same amino acid.
• Frameshift mutations - 1 or more nucleotide is either inserted or deleted. This pushes the whole base sequence either to the left, in deletion, or the right, in insertion.
• Frameshift mutations change the whole sequence of amino acids after the mutation, changing the protein's primary and tertiary structure.
• Which type of mutation is more likely to cause changes to a protein produced?

  Frameshift mutations.
• Which levels of protein structure can be affected by a mutation?

  Primary (1*) and tertiary (3*).
• What is a mutagenic agent?

  A mutagenic agent is a substance or factor that can cause changes in the DNA sequence, leading to mutations.
• Name some mutagenic agents.

  -Cigarette tar

  -Radiation (UV, Gamma, X-Rays, Alpha and Beta particles etc) -Heavy metals (mercury, lead)

  -Some chemicals (asbestos)
• Some mutations are not changes to the base code (gene mutations) but are mutations of the number of chromosomes passed on from one generation to the next. These are chromosome mutations.
• Non-disjunction is the failure of homologous chromosomes to separate during meiosis.
• Plants often have more than the expected number of chromosomes, and this is called polyploidy.
• Triploid: (of a cell or nucleus) containing three homologous sets of chromosomes (one extra pair).
• Tetraploid: containing four homologous sets of chromosomes (two extra pairs).
• Down Syndrome is known as trisomy 21, as it is caused by an extra chromosome number 21.
• A person with Down Syndrome has 47 chromosomes instead of 46.
• Edward's Syndrome is also known as trisomy 18, as it is caused by an extra chromosome number 18.
• Characteristics of Edward's Syndrome include:

  -Cleft lip/palate

  -Microcephaly

  -Malformation of the hands and feet

  -Neural tube defect

  -Malformation of the sex organs
• In Edward's Syndrome, survival beyond the neonatal period is uncommon.
• Patau Syndrome is also known as trisomy 13, as it is caused by an extra chromosome number 13.
• In Patau Syndrome, survival beyond the neonatal period is uncommon.
• Characteristics of Patau Syndrome include:

  -Microcephaly

  -Abnormal openings in the skull

  -Malformations of the brain

  -Cleft lip/palate

  -Structural defects of the eyes

  -Polydactyly

  -Congenital heart defects

  -Neural tube defect

  -Malformation of sex organs
• Jacob's Syndrome is caused by an extra Y chromosome (XYY) and is noted for infertility and anti-social behaviour.
• What is non-disjunction?


  When parent chromosomes fail to separate.