Topic 6 - Mutations and Gene Pools Flashcards
(21 cards)
What is a mutation?
Is a permanent change in the DNA sequence that can result in the formation of a new allele. It introduces genetic variation, which may affect the organism’s traits and can be beneficial, harmful or neutral.
What is a mutagen?
It is a physical, chemical, or biological agent that increases the rate of mutation.
How are mutations caused?
1) Spontaneously
2) Induced
How are mutations spontaneously caused?
It is due to random errors in DNA replication, cell division (mitosis, or meiosis).
How are mutations induced?
Mutations are caused by the environment through to the exposure to mutagens such as:
- Ionising radiation (UV light, X-rays, gamma rays)
- Chemical mutagens (mustard gas, formaldehyde)
- Biological agents like viruses
How does electromagnetic radiation (EMR) cause DNA damage?
- Breaking chemical bonds within the DNA molecule, especially in the sugar-phosphate backbone.
- Causing base alterations, leading to incorrect base pairing during DNA replication.
- Creating thymine dimers (in the case of UV radiation) – two adjacent thymine bases bond together, distorting the DNA strand and blocking transcription and replication.
How do chemical mutagens cause DNA damage?
- Chemically modify DNA bases, leading to incorrect base pairing during replication.
- Insert between bases (intercalating agents), distorting the double helix and often causing frameshift mutations.
- Inhibit enzymes involved in DNA repair, making mutations more likely to persist.
What are the types of cells affected?
1) Somatic
2) Germline
What are somatic mutations?
Mutations that only occur in body (somatic) cells. This mutation usually only affects the individual and is lost when they die. This means somatic cell mutations can’t be passed on to offspring and are not inherited.
What are germline mutations?
Mutations that occur in reproductive cells (gametes – sperm and egg). This mutation doesn’t affect the individual but will be passed on to offspring, affecting future generations.
What are the different sections DNA can be affected by mutation?
1) Gene Mutation
2) Point Mutation
3) Chromosomal Mutation
What is gene mutation?
Affects a single gene which may result in a missing or malfunctioning protein.
What is a point mutation?
Affects one nucleotide. This includes substitution and frame shift mutation (insertion and deletion).
What is substitution?
When one base is substituted with another base. Substitution mutations only affect the transcription and translation of a single codon, leaving the remaining codons of the gene unaffected.
What is a chromosomal mutation?
Affects large sections of DNA or whole chromosomes. This may involve:
- Changes in structure (inversion, translocation)
- Changes in number (trisomy, monosomy)
What are the different types of point mutations?
1) Missense Mutation
2) Nonsense Mutation
3) Neutral Mutation
4) Silent Mutation
5) Frameshift Mutation
What is a missense mutation?
Mutations that cause a change in the amino acid produced and therefore the entire protein.
What is a nonsense mutation?
A change in base accidentally codes for the stop codon, which causes the translation of a protein to stop prematurely.
What is a neutral mutation?
The mutation causes a change in the amino acid produced. However, the amino acid is of the same type as the correct amino acid and does not change the structure and function of the protein.
What is a silent mutation?
Mutations that do not cause a change in the amino acid and proteins produced. This is because most amino acids are coded for by more than one base.
What is a frameshift mutation (insertion and deletion)?
Is the addition or deletion of a single nucleotide. Bases are read in groups of 3 because 3 bases code for a single amino acid (the building blocks of protein). So, by adding or removing a nucleotide, the subsequent bases will be read in the incorrect ‘group of 3’, potentially changing the amino acid and proteins produced.
