inquiry q1: how does mutation introduce new alleles into a population? Flashcards
Mutation
A mutation is a change in the genetic material of a cell. This happens when the sequence of nucleotides in DNA is altered, changing the gene coded, therefore the protein or RNA end product.
* It can occur spontaneously due to errors in meiosis or mitosis, natural degradation over time, or induced by environmental agents known as mutagens.
Mutagen
A mutagen is any environmental agent that has the potential to cause a mutation.
* Mutagenesis is the process of mutations that change normal base pairs to altered base pairs.
Eg. A carcinogen is a mutagen and a chemical that can cause cancer (causes mutations in genes that aid the repair of DNA).
Type of mutagens:
Physical Mutagens
Particle radiation (nuclear power plants, nuclear weaponry)
* Particle radiation is the energy that is emitted by fast-moving subatomic particles. Particle radiation is produced by nuclear fission and fusion and is an extremely powerful mutagen.
High energy EM radiation (UV, x-rays, gamma rays)
- Non-ionising radiation
- UV radiation is non-ionising but still penetrates skin and has enough energy to hit DNA.
Ionising radiation
Ionising radiation occurs in physical mutagens, causing atoms to vibrate and lose electrons, breaking bonds and damaging DNA. Multiple fractures in the DNA can overwhelm enzymes causing mistakes to be made and mutations to occur.
Types of mutagens:
Chemical mutagens
Chemical interact with DNA by:
* tricking the DNA into thinking they’re a part of it
* changing the nucleotides
* directly getting in between nucleotides
This causes misreading and changes in polypeptide synthesis. Chemical mutagens are often ingested (like alcohol and tobacco) or environmental (like cleaning products, asbestos, lead).
Types of chemical mutagens
Intercalating agents
* Chemicals that insert themselves into the bonds between base pairs and alter the shape of the DNA, leading to subsequent errors in replication.
Base analogues
* Chemicals that are structurally similar enough to the nitrogenous bases in DNA that they are incorporated into the DNA sequence during replication instead of the usual bases, meaning that the DNA no longer functions.
DNA reactive chemicals (reacting chemicals)
* Chemicals that react directly with DNA that cause breakages and cross-links in DNA strands.
* e.g. ROS (reactive oxygen species), highly reactive molecules containing oxygen, while ROS are produced during normal cellular function, excessive amounts are thought to contribute to the development of cancer.
Biological mutagens (naturally occuring mutagens)
Biological mutagens are living molecules that can cause mutations and cancers by interfering with the functions of oncogenes and tumour-suppressor genes.
Oncogenic virius
* During the viral replication process, certain virus’s DNA or RNA affects the host cell’s genes in ways that may cause it to become cancerous.
Transposable element
* Short DNA sequences that move around the genome, extremely common in eukaryotic genomes, causes errors in replication and interfere in the functing od certain genes, multiple copies of the same sequence can change chromosome crossover points and cause errors in chromosome duplication.
Point mutations
Point mutation involves changing one or very few nucleotide bases in a gene sequence.
* Type of point mutations are substitution and frameshift mutations (insertations and deletions).
Point mutation:
Substitution
Substitution: When one base is changed to a different base in a DNA sequence.
1. Silent mutation: results in a new codon that still codes for the same amino acid.
2. Missense mutation: results in an amino acid being replaced, will still produce a protein but may not function properly.
3. Nonsense mutation: results in an amino acid being changed to a stop condon, results in an incomplete amino acid and usually non-functional proteins.
Point mutation:
Frameshift Mutations (Insertions and Deletions)
Both insertion and deletion cause a massive impact as they result in a frameshift where every codon from that point on is affected, which means that incorrect amino acids are being created, resulting in non-functional proteins.
* Insertions: when one base is added to DNA sequence
* Deletions: when one base is removed from the DNA sequence
Chromosomal Mutations
Chromosomal mutations involves large scale mutations that affect the overall structure of a chromosome or the entire number of chromosomes in a cell are altered.
Types of chromosomal mutations:
Aneuploidy (Numerical abnormalities)
Nondisjunction of chromosomes during meiosis, when homologous chromosomes or sister chromatids fail to separate, results in mutant gametes which can result in offspring containing extra or less chromosomes.
Types of chromosomal mutations:
Polyploidy (Structural abnormalities within chromosomes)
Chromosomes have sections deleted, duplicated, or translocated from one chromosome to another, or chromosomes being inverted to face the opposite direction.
* Deletion: Loss of part or all of chromosomes → will affect the growth and development of an organism.
* Duplication (replication): Copy of all or part of chromosome → will increase gene expression, could be either beneficial or harmful depending on the gene.
* Inversion: Reverses direction of parts of chromosome → lowers fertility due to production of unbalanced gametes
* Insertion: section of chromosome breaks off and attaches to a different chromosome → results in gametes with two copies of the genes in the inserted section or may be missing the genes entirely
* Translocation: Two chromosomes exchange segments with each other → will interrupts gene regulation and could cause some forms of cancer.
Types of chromosomal mutations:
Trisomy
Where there is an extra copy of a chromosome present, can lead to shortened life span or development problems
e.g. Down syndrome
Somatic mutations
- Occurs in somatic cells (body cells)
- Affects the individual and cannot be inherited by offspring nor passed on to the next generation
- Mutated cells can divide, growing tissue with this error (cancer)
- Caused by environmental factors
