Mutations and genetic diversity Flashcards
Mutation definition
Change in a DNA base sequence
How do gene mutations result in a non-functioning protein?
Change in the DNA base sequence changes amino acid sequence which changes tertiary structure and function of protein
Why could a mutation potentially not change the function of a protein?
DNA is degenerate
Substitution mutation definition
One base is substituted for another base
Frame shift mutation definition
One base is added or deleted, meaning all the triplets/codons following the mutation will change
Mutagenic agent definition
Increase the chance of mutations
What are 4 examples of mutagenic agents?
- Ionising radiation
- UV radiation
- Some viruses
- Some chemicals
What is chromosome non-disjunction?
Homologous chromosomes/sister chromatids aren’t separated during meiosis
What is the result of chromosome non-disjunction?
One gamete will have an extra chromosome, one gamete will have one less chromosome
Genetic diversity definition
The number of different alleles of genes in a population
How is genetic diversity increased?
- Random mutation in DNA
- Different alleles being introduced (gene flow)
How is genetic diversity reduced?
Geographical isolation or population reduction
How does geographical isolation reduce genetic diversity?
- A few organisms are geographically isolated
- Only a small number of DIFFERENT alleles from the original gene pool
- Gene pool may not be representative of population they came from
How does reduced population reduce genetic diversity?
- Event occurs which causes a huge reduction in a population
- Reduces number of DIFFERENT alleles in a gene pool
- Survivors reproduce, creating a larger population from a few individuals
What are the consequences of low genetic diversity?
- Greater incidence of genetic disease
- If environment changes, population has less ability for natural selection
What is the anagram for natural selection?
Mass Rift
Mutations (already present)
Alleles (advantage)
Selective advantage/pressure (environment change = different selective pressure)
Survive
Reproduce
Inherit alleles
Frequency of alleles increases
Time (over many generations)
What are the 3 types of adaptation?
Behavioural, physiological and anatomical
What is stabilising selection?
*Occurs in populations where the environment is stable
*Selective pressure at both ends of the distribution (e.g. low/high birth mass less likely to survive)
*Favours the average (e.g. middle birth mass)
*Tends to eliminate extremes (too high/low)
*Reduces variability, opportunity for evolutionary change and the range of possible characteristics
What is directional selection?
*Mutation already present
*Environmental change produces a new selective pressure (e.g. antibiotics) that favours an extreme characteristic (e.g. high resistance allele)
*Over time selection means these will predominate and the mean will shift
E.g. Antibiotic resistance allele of bacteria
What is disruptive selection?
Favours BOTH extremes and could lead to SPECIATION
How do bacteria obtain multiple antibiotic resistance?
Random Mass Rift to antibiotic A
THEN
NEW random Mass Rift to antibiotic B (NEW selective pressure)
What is vertical gene transfer?
Antibiotic resistance alleles are in PLASMIDS, passed through BINARY FISSION
What is horizontal gene transfer?
- Antibiotic resistance allele normally found on plasmid
- Plasmid replicates
- Pilus forms a conjugation tube between the resistant bacterium and another bacterium
- Copy of the plasmid DNA passes through the tube
- Both bacterial cells now contain the allele for antibiotic resistance
What 3 genetic factors cause genetic diversity/variation?
- Crossing over
- Random fertilisation of gametes
- Independent segregation
