Genetic Diversity & Adaptation (AQA A Level Biology): Flashcards
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Define genetic diversity.
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Define genetic diversity.
Genetic diversity is the number of different alleles of genes in a population.
Define genetic variation.
Genetic variation is the small differences in DNA base sequences between individual organisms within a species population.
Define the fitness of an organism.
The fitness of an organism is its ability to survive and pass on its alleles to offspring.
What is the source of new alleles in a population?
Mutation results in the generation of new alleles.
This contributes to genetic diversity, or the size of the gene pool.
Why might a new allele not be seen in the individual in which it first occurs?
The new allele can remain hidden (not expressed) within a population for several generations before it contributes to phenotypic variation.
True or False?
A population with high genetic diversity has a strong ability to adapt to change.
True.
A population with a large gene pool (high genetic diversity) has a strong ability to adapt to change.
Why is a population with a small gene pool vulnerable to extinction?
With very low genetic diversity, the population is much less able to adapt to changes in the environment.
This makes it less likely to survive if environmental conditions change.
Why is some level of genetic diversity needed for natural selection to occur?
Differences in the alleles possessed by individuals result in differences in phenotypes.
Selection pressures can then increase the chance of individuals with a specific phenotype surviving and reproducing.
Why are cheetahs an example of a species with low genetic diversity?
A large decline in numbers around 10,000 years ago left small, fragmented populations with no mixing and large amounts of inbreeding.
Their resulting small gene pool means they are less likely to survive environmental changes.
Genetic diversity is defined as the number of different of genes in a population.
Genetic diversity is defined as the number of different alleles of genes in a population.
Why are logarithmic scales useful when investigating bacterial numbers?
Bacterial colonies can grow rapidly, producing a wide range of very small and very large numbers.
A logarithmic scale allows this wide range of values to be displayed on a single graph.
What is meant by an order of magnitude?
An order of magnitude means a tenfold (×10) change in quantity.
On a base 10 (log₁₀) scale, what does each unit step represent?
Each unit step represents one order of magnitude (a tenfold change).
How can you identify a logarithmic scale on a graph?
There are not equal (uneven) intervals between the numbers on the axis.
True or False?
The pH scale is a logarithmic scale.
True.
The pH scale is logarithmic; the concentration of hydrogen ions varies massively between each pH level.
Why can a linear scale be difficult to use for bacterial growth data?
There is a wide range of very small and very large numbers.
This makes it hard to work out a suitable scale for the axes of a graph.
In the yeast culture example, what was done to the cell numbers before plotting them on a log scale?
The number of yeast cells at each time interval was converted to a logarithm before being plotted.
Will you be expected to convert values into logarithms in the exam?
No.
You may instead be asked to interpret results that use logarithmic scales, or to explain the benefit of using one.
An order of magnitude means a change in quantity.
An order of magnitude means a tenfold (×10) change in quantity.
Outline the principles of natural selection.
Random mutation can produce new alleles of a gene.
Under certain environmental conditions, a new allele may benefit its possessor, increasing its chance of survival and reproductive success.
The advantageous allele is passed on to the next generation.
Over several generations, the new allele increases in frequency in the population.
What is meant by differential reproductive success?
Individuals with different alleles of the same gene have different degrees of reproductive success.
Under certain environmental conditions, individuals with certain alleles have an increased chance of survival and reproduction.
Why does genetic variation exist within populations?
Genetic variation exists due to the presence of different alleles.
True or False?
Natural selection can cause the frequency of alleles in a population to change over time.
True.
Natural selection can cause the frequency of alleles in a population to change over time.
In the rabbit example, why does the frequency of alleles for brown fur increase over generations?
White rabbits do not camouflage as well, so predators are more likely to see them.
Brown rabbits have a selection advantage, so they are more likely to survive to reproductive age and pass on their alleles.
Over many generations, the frequency of alleles for brown fur increases.
Are most mutations beneficial to an organism?
No.
Many mutations are harmful or neutral, but under certain environmental conditions a new allele may benefit its possessor.
What acts as the selection pressure in the rabbit fur-colour example?
Natural predators, such as foxes, act as the selection pressure.
How is an advantageous allele passed to the next generation?
Through reproductive success - individuals with the advantageous allele survive and reproduce, passing the allele to their offspring.
Over several generations, an advantageous allele will increase in in the population.
Over several generations, an advantageous allele will increase in frequency in the population.
What is a selection pressure?
A selection pressure is an environmental factor that affects the chance of survival of an organism.
Define stabilising selection.
Stabilising selection is natural selection that keeps allele frequencies relatively constant over generations.
Define directional selection.
Directional selection is natural selection that produces a gradual change in allele frequencies over several generations.
Give the classic example of stabilising selection.
Human birth weights.
Very-low and very-high birth weights are selected against, and the intermediate (medium) birth weights are maintained.
Give the classic example of directional selection.
Antibiotic resistance in bacteria.
The presence of antibiotics acts as a selection pressure, increasing the frequency of the beneficial resistance allele over generations.
Explain how directional selection leads to antibiotic-resistant bacteria.
The presence of antibiotics is a selection pressure.
Random mutation produces a beneficial allele conferring antibiotic resistance.
Bacteria with this allele are more likely to survive and reproduce, while most without it die.
Over generations, the frequency of the beneficial resistance allele increases.
In stabilising selection of human birth weight, why are very low and very high birth weights selected against?
Very low birth weight carries a higher risk of health problems and death.
Very high birth weight may cause complications during birth, also increasing mortality risk.
Medium birth weights have the highest survival rates.
True or False?
Directional selection causes the mean trait value of a population to change over time.
True.
Directional selection favours one extreme phenotype, causing the mean trait value in the population to change over time.
When does directional selection usually occur?
When there is a change in the environment / selection pressures, or when a new advantageous allele appears in the population.
Stabilising selection keeps allele frequencies relatively over generations.
Stabilising selection keeps allele frequencies relatively constant over generations.
What are the three types of adaptation?
Anatomical, physiological and behavioural.
What is an anatomical adaptation?
An anatomical adaptation is a structural feature of an organism's body that helps it survive.
For example, the white fur of a polar bear provides camouflage in the snow.
What is a physiological adaptation?
A physiological adaptation is an internal biological process that increases survival or reproduction.
For example, mosquitoes produce chemicals that stop blood clotting so they can feed more easily.
What is a behavioural adaptation?
A behavioural adaptation is an action or behaviour that helps an organism survive.
For example, cold-blooded reptiles bask in the sun to absorb heat.
Which type of adaptation is the migration of birds to warmer climates?
A behavioural adaptation.
How does natural selection make a species better adapted to its environment?
A favourable allele produces an advantageous feature, so those individuals are more likely to survive.
They produce more offspring, so the allele frequency increases in the population.
Natural selection selects against unfavourable alleles, so their frequency decreases.
Over time the adaptation becomes more common and the species becomes better suited to its environment.
Define evolution.
Evolution is the change in adaptive features of a population over time as a result of natural selection.
Why does evolution not occur if an environment is static?
If the environment does not change, the selection pressures will not change, so evolution will not occur.
When are two isolated populations of one species considered two new species?
When they become so different in phenotype that they can no longer interbreed to produce fertile offspring.
True or False?
Adaptation and selection are major factors in evolution and contribute to the diversity of living organisms.
True.
Adaptation and selection contribute to the large diversity of living organisms and are major factors in evolution.
The formation of new species from pre-existing species over time is called .
The formation of new species from pre-existing species over time is called speciation.
Why must aseptic techniques be used when investigating microbial growth?
To ensure the microbes being investigated don't escape or become contaminated with another unwanted, and possibly pathogenic, microbe.
Why should you work next to a lit Bunsen burner during inoculation?
It creates convection currents that stop contaminants from falling onto the growth media.
Why are inoculating loops heated until red-hot before and after use?
Heating the loops until red-hot kills any unwanted microorganisms, preventing contamination.
Why is the Petri dish lid lifted at an angle during inoculation, rather than fully removed?
This reduces the contamination risk from airborne microorganisms.
Why are plates incubated at a safe temperature of 25 °C rather than body temperature?
This prevents the growth of pathogenic microorganisms, which are more likely to grow at human body temperature.
Why are Petri dish lids taped closed after plating?
Loss of the Petri dish lids could lead to the escape of potentially harmful microorganisms.
How is the size of a zone of inhibition measured and compared between antibiotics?
Measure the diameter (or radius) of the clear zone and calculate its area (πr²).
Use the mean of repeated plates for each antibiotic to allow a fair comparison.
What control should be included in an antibiotic disc-diffusion experiment?
A disc soaked in sterile water (no antibiotic).
It should produce no zone of inhibition, showing that any effect is due to the antibiotic and not the disc itself.
What does a larger clear zone around an antibiotic disc indicate?
A more effective antibiotic, or bacteria that are more sensitive to it.
The antibiotic inhibits bacterial growth over a wider area around the disc.
What is the zone of inhibition in a disc diffusion experiment?
The clear area around a paper disc where there are no bacteria present.
It is where the antibiotic concentration is high enough to prevent bacterial growth.
True or False?
If bacteria are completely resistant to an antibiotic, there will be a large clear zone around the disc.
False.
If bacteria are completely resistant to an antibiotic, there will be no clear zone around that disc.
Work surfaces should be treated with disinfectant or alcohol before to reduce contamination.
Work surfaces should be treated with disinfectant or alcohol before inoculation to reduce contamination.
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