What is genetic diversity in a population?
The number of different alleles of genes present in the population.
AQA A-Level Biology - (7402) · 3.4.4
Revise AQA A-Level Biology - (7402) specification point 3.4.4, Genetic diversity and adaptation, with free active-recall flashcards. Flip through the set or review every question and answer below.
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What is genetic diversity in a population?
The number of different alleles of genes present in the population.
What kind of variation does genetic diversity provide among individuals?
Heritable variation.
Under what condition can an allele’s frequency change through natural selection?
When the allele affects reproductive success in a particular environment.
How can natural selection increase the frequency of an advantageous heritable allele?
Individuals with the allele may survive and reproduce more successfully, passing it to offspring. Over generations, the allele can become more frequent.
How can new alleles arise?
Through random mutations.
Do mutations arise because an organism needs them?
No. Mutations do not arise in response to an organism’s needs.
Are mutations always advantageous?
No. Many mutations are harmful.
What determines whether an allele is advantageous?
The environment in which it occurs.
What does natural selection contribute to over generations?
Evolution and the diversity of living organisms.
How can population data be assessed for consistency with natural selection?
Compare frequencies or characteristics over time and consider whether the observed change is consistent with selection.
What is directional selection?
Individuals at one end of a range of variation have greater reproductive success, shifting the distribution of a heritable characteristic over generations.
How can an antibiotic affect resistant and susceptible bacteria differently?
A resistant bacterium may survive and reproduce, while susceptible bacteria are inhibited or killed.
Why can resistant bacteria become a larger proportion of an antibiotic-exposed population?
Surviving resistant bacteria reproduce and pass resistance alleles to their descendants.
Does an antibiotic produce resistance mutations because bacteria need them?
No. The antibiotic selects resistant bacteria; it does not produce a mutation because bacteria need it.
What is stabilising selection?
Selection in which individuals with intermediate values of a heritable characteristic have greater reproductive success than those at either extreme.
What effect does stabilising selection tend to have on a population’s characteristic and its variation?
It maintains the intermediate form and reduces variation.
How does human birth weight illustrate stabilising selection?
Historically, babies with very low or very high birth weights had lower survival than those with intermediate birth weights.
What is an adaptation?
An inherited feature that makes an organism better suited to its environment and can increase its reproductive success there.
What are the three types of adaptation, and what does each involve?
How can natural selection make a population better adapted over generations?
It can increase the frequency of alleles associated with advantageous features.
How do adaptation and selection relate to evolution and the diversity of living organisms?
Together, they contribute to evolution and the diversity of living organisms.
What is the aim of aseptic technique when investigating microbial growth?
To minimise contamination of the culture and surroundings.
What three practices help maintain aseptic conditions when working with cultures?
Use sterile equipment and media, keep exposure of sterile materials brief, and handle and dispose of cultures safely.
How can antimicrobial substances be applied to an agar culture for comparison?
Place sterile discs containing the substances on an inoculated agar plate alongside an appropriate control disc, then incubate under suitable safe conditions.
What does a clear zone around a disc on an inoculated agar plate indicate?
Inhibition of visible microbial growth.
How can inhibition zones be used to compare antimicrobial treatments?
Measure their diameters and compare them with the control and with other treatments.
Why should antimicrobial tests be repeated?
Repeats improve confidence in the pattern of results.
Which three conditions should be kept consistent for a fair comparison of antimicrobial treatments?
The microorganism, the amount of inoculum, and the incubation conditions.
Why might the size of an inhibition zone not reflect antimicrobial effect alone?
Zone size is also affected by how readily the substance diffuses through the agar.