3.4.3 Genetic diversity can arise as a result of mutation or during meiosis Flashcards
Gene mutations
A change in the DNA base sequence of chromosomes - any change to one or more nucleotide bases or any rearrangement of bases in DNA
What stage of the cell cycle do gene mutations arise spontaneously?
DNA replication –> Synthesis Phase of Interphase
Why might a mutation not lead to change in the amino acid sequence?
- Genetic code is degenerate: mutation may end up coding for the same amino acid as the original triplet
- Mutation may occur in intron (non-coding for polypeptides)
What are the factors that contribute to the likelihood of mutations?
- High energy radiation (X-rays, gamma rays)
- High energy particles (ionized and radioactive energy particles)
- Mutagenic agents/carcinogens (e.g tar in cigarette smoke)
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another.
In regards to substitution mutation, what are the three types of mutations as a consequence?
- Silent mutation
- Mis-sense mutation
- Nonsense mutation
What is a silent mutation?
No change in the amino acid (same amino acid as the original triplet)
What is a nonsense mutation?
A stop codon is produced
What is a mis-sense mutation?
A different amino acid is produced.
Describe the effect that a mis-sense mutation has on the formation of a protein?
- Different amino acids —> different protein produced
- Primary structure is affected
- Secondary structure is affected: different R-groups/H-bonds/ionic bonds/disulphide bridges.
- Tertiary structure is affected – folding of protein
What is a deletion mutation?
When a nucleotide is lost from the original DNA sequence
What is a frame shift?
When ALL the amino acids after the point of mutation will be in the wrong triplet
Why is a deletion mutation more harmful and significant than a substitution mutation?
Frame shift means the entire amino acid sequence will be different
What is an addition mutation?
When a nucleotide is added to the original DNA sequence –> frame shift changing the entire amino acid sequence after the point of mutation
What are mutagenic agents?
Factor that increase the rate of gene mutation
What are chromosome mutations?
Errors during meiosis with the gametes produced containing variations in the numbers of whole chromosomes or parts of chromosomes
What is chromosome non-disjunction?
Pairs of chromatids that do not separate in meiosis, resulting in gametes with one more or one less chromosome than normal
What are the examples of non-disjunction disorders?
- Down syndrome: extra chromosome 21
- Patau’s syndrome: extra chromosome 13
- Edward’s syndrome: extra chromosome 18
- Kleinfelters
- Turners
