Module 6 Flashcards
Explain how mutagens from electromagnetic radiation sources work.
Ionising radiation such as x-rays, γ rays, α particles and β particles, can damage DNA Directly; Ionisation of molecules in the DNA, resulting in the sugar-phosphate backbone breaking, or a nitrogenous base changing so that it no longer pairs with its complementary base; Or Indirectly; Ionising other molecules in the cell, sometimes producing free radicals which can interact with other molecules to form compounds (such as H2O2) which can damage DNA.
Explain how naturally occurring mutagens work.
Naturally occurring mutagens are spontaneous and cause DNA replication errors which are retained because the normal mechanism of DNA repair does not correct them. Examples of naturally occurring mutagens of biological origin include various toxins produced by living organisms, such as alkaloids produced by plants such a bracken ferns, and mycotoxins produced by fungi.
Explain how chemical mutagens work.
Chemical mutagens are chemicals that cause mutations if cells are exposed to them for a long period of time. They cause DNA change by altering the function of proteins and therefore impairing cellular processes. Examples include; Heavy metals - which can cause the sugar-phosphate backbone of DNA to break or inhibit enzymes which repair DNA and Deaminating agents like nitrous acid (converts C to U).
What causes a point mutation? What is the effect of a point mutation? Name the types of point mutations.
A point mutation is a change in a single nucleotide base pair in DNA or RNA and is an example of a small-scale gene mutation. They are spontaneous. They can be harmful, neutral or beneficial depending on the type of point mutation; Nonsense, missense or silent. Silent mutations will have no effect. A nonsense mutation can cause a genetic disease such as cystic fibrosis.
What causes a chromosomal mutation? What is the effect of a chromosomal mutation? Name the types of chromosomal mutations.
A chromosomal mutation is a large-scale alteration, being a structural and/or numerical change in the entire DNA strand. Some chromosomal mutations involve a change in chromosome number. Types of chromosomal mutations include; deletion, duplication, inversion and translocation.
Compare somatic and germline mutations in relation to their effect on an organism.
Similarities
- Both occur during cell replication
Somatic mutation
- Occurs in non-reproductive/body cells
- cannot be transferred to future gens
- Occur during mitosis when DNA replication occurs
- Affects all cells from original mutated cell
- Can show harmful effects; damage caused to cells, cancerous growth, cell death.
- May result in physiological changes
- Mostly neutral, contribute to genetic diversity
- Do not directly change allele frequency in gene pool
Germline mutations
- Occurs in gametes during meiosis
- Passed on to offspring
- Resulting embryo will have mutation in every cell
- Can change allele frequency in a gene pool, e.g DDT resistance in mosquitoes
- Examples of inherited diseases include; cf, huntingtons, thalasssemia
What is a mutation?
A mutation is any change to the DNA of an organism, that is unpredictable and random. That is, it cannot be predicted which gene will be affected, and how it will be affected. Most mutations have no effect on the organism. Some result in a phenotypic change to the individual.
Why are ‘coding’ DNA segments significant in the process of mutation?
Exons or ‘coding’ DNA affect phenotype due to their direct effect on proteins.
What would you expect to happen to the translated DNA sequence if an intron was modified by a mutagen?
A mutation in an intron or non-coding DNA segment usually will have no phenotypic effect whatsoever on an organism, as introns are spliced out during RNA processing.
What would you expect to happen to the translated DNA sequence if an exon was modified by a mutagen?
A missense, non-sense or silent mutation would occur. Depending on which mutation resulted the effect would be different. A missense mutation is a mutation in which the wrong amino acid is encoded, therefore a change to the DNA results in a protein that is also changed. A nonsense mutation is a point mutation that creates a stop codon, therefore, the DNA sequence would be cut short. A silent mutation produces no change to the polypeptide encoded, because the genetic code is degenerate (or “redundant”).
How does fertilisation contribute to genetic variation?
Fertilisation increases genetic variation in the population as it creates a new gene combination through the mixing of maternal and paternal genetic material, therefore adding new gene combinations to the population.
How does meiosis contribute to genetic variation?
Meiosis contributes to genetic variation through the processes of independent assortment, crossing over of alleles and random segregation of chromatids, which allows different combinations of genetic material to be produced in gametes. These genetically unique gametes then combine with other genetically unique gametes to produce an embryo with its own unique set of genes during fertilisation, thus contributing to increasing genetic diversity in the population.
How do mutations contribute to genetic variation?
Mutations are a permanent change in the DNA, and they can be random. Mutations in somatic cells do not introduce genetic variation into a population. Mutations during meiosis lead to genetic diversity in a population as these mutations are inheritable, and cause changes in the phenotypes of offspring. Point mutations during DNA replication during meiosis contribute to genetic variation as they form new alleles. Mutations can also have no effect on variation at all.
Evaluate the effect of a mutation on the gene pool of a population.
- A mutation can have no effect, however, it can also introduce new alleles due to changes in DNA.
- Most are harmful, confer poor fitness and will be lost from a gene pool over a few generations.
- Some are neutral and have no advantage, they provide variation that have no effect but may provide an advantage in the future in the environment changes suddenly.
- Some improve fitness and will increase in frequency with each generation, at the expense of other alleles.
Evaluate the effect of gene flow on the gene pool of a population.
- Gene flow occurs when genes are exchanged with other gene pools
- It adds/takes away alleles from a population, thus changing allele frequencies.
- Two-way movements may cancel each other out, resulting in no effect.
Evaluate the effect of genetic drift on the gene pool of a population.
- Genetic drift occurs when chance events, e.g a natural disaster, cause allele frequencies of small populations to ‘drift’ from one generation to the next.
- It tends to decrease the genetic diversity in a gene pool
-There are two ways in which genetic drift can affect the gene pool of a population: (1) the founder effect
and (2) a genetic bottleneck.
1) The founder effect happens when a new population is formed from a small number of individuals from an existing parent population, but the genetic make-up of these ‘founding’ individuals is not representative of the existing population.
2) A genetic bottleneck occurs when a population on the brink of extinction grows in numbers again, but the frequency of alleles is changed because the few individuals that survived give rise to the new population which is not representative of the genetic make-up of the original population.
