The Development of Understanding of Genetics & Evolution (AQA GCSE Biology)
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How did Darwin develop his theory of natural selection?
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How did Darwin develop his theory of natural selection?
Darwin developed his theory by:
making observations
carrying out experiments
building on his knowledge of geology and fossils
True or False?
Natural selection can occur in a population of genetically identical individuals.
False.
Natural selection can only occur when variation is present. This is why populations with no, or limited, genetic variation are unable to adapt to changes in their environment.
Describe the process of natural selection.
Darwin's theory of natural selection states that:
Individuals within a species exhibit variation due to genetic differences
Those with advantageous traits are more likely to survive and reproduce
The alleles that code for advantageous traits are passed on to offspring
Over time the advantageous alleles become more common in the population
Why was acceptance of Darwin's theory of evolution so gradual?
Darwin's theories were accepted gradually during his lifetime due to:
existing beliefs about God and creation
a lack of sufficient evidence to back up his ideas
a lack of understanding of genetic variation and the mechanisms of inheritance
Why is Lamarck's theory of evolution incorrect?
Lamarck's theory of evolution is incorrect because it suggests that characteristics gained during an organism's lifetime can be passed on to offspring; we now know that such acquired characteristics cannot be inherited in this way.
True or False?
Alfred Russel Wallace and Charles Darwin worked together to propose the theory of evolution by natural selection.
False.
Alfred Russel Wallace proposed his theory of natural selection independently of Darwin.
For which of his work is Wallace best known in the scientific community?
Wallace is best known for his work on:
warning colouration in animals
speciation
Define the term speciation.
Speciation is the process by which new species arise from existing species.
What are the events in the image below that result in speciation?
The events of speciation shown in the diagram include:
a population is separated by a mountain range
the two halves of the population are exposed to different environmental conditions, meaning that natural selection acts differently on each new population
over time the two new populations become so different that they can no longer breed together; speciation has occurred
Mendel observed that the inheritance of plant characteristics was determined by 'units' that were passed from parents to offspring.
What are the units which he referred to?
The units referred to by Mendel are alleles which are passed from parents to offspring.
True or False?
Mendel observed the behaviour of chromosomes during cell division.
False.
Mendel worked during the mid 19th century and the behaviour of chromosomes during cell division was not observed until the late 19th century.
What 20th century observation caused scientists to conclude that genes are located on chromosomes?
Scientists concluded that genes are located on chromosomes due to the observation that chromosomes behaved in a similar way to the 'units' described by Mendel.
What is gene theory?
Gene theory covers the concept that traits are passed from parents to offspring through gene transmission
What sources of evidence have aided the acceptance of Darwin's theory of evolution by natural selection?
Evidence that has aided the acceptance of Darwin's theory of evolution by natural selection include:
the fossil record
development of antibiotic resistance in bacteria
the inheritance of parental genes by offspring
Define the term fossil.
Fossils are the remains of organisms from millions of years ago found in rocks.
True or False?
Trace fossils form when parts of dead organisms are preserved by being replaced by minerals.
False.
Trace fossils are not preserved parts of organisms, but are indications of their presence, e.g. burrows or footprints.
How do fossils form?
Fossils can form when:
the conditions for decay are absent, preserving parts of organisms
parts of organisms are replaced by minerals as they decay
True or False?
The fossil record shows scientists how life on earth began.
False.
Early life forms had soft bodies which did not fossilise, meaning that the fossil record does not show how life began.
What can be learned about evolution from looking at the fossil record?
The fossil record shows how species have changed over time.
What does the evolutionary tree below show about the five primate species?
The evolutionary tree shows that:
all five primate species share a common ancestor
chimpanzees and bonobos share the most recent common ancestor
humans, chimps and bonobos share a more recent common ancestor with gorillas than with orangutans
Define the term extinction.
Extinction has occurred when there are no living members of a species remaining.
Which factors can contribute to the extinction of a species?
Factors that contribute to extinction include:
disease
predation
more successful competitors
environmental change that is too fast for natural selection to occur
natural disasters, e.g. asteroid impact or volcanic activity
What is antibiotic resistance?
Antibiotic resistance is the ability of bacteria to withstand the effects of an antibiotic; bacteria with resistance to a particular antibiotic are more likely to survive when they are exposed to the drug.
Why can antibiotic resistance in bacteria evolve quickly?
Antibiotic resistance can evolve quickly because of the rapid reproduction rate of bacteria.
True or False?
Mutation can result in antibiotic resistance in bacteria.
True.
Random mutations in bacterial DNA can lead to antibiotic resistance, enabling some bacteria to survive antibiotic treatment.
How can an antibiotic resistant population of bacteria arise?
Antibiotic resistant strains of bacteria can arise by the following process:
Mutation gives rise to an allele that codes for antibiotic resistance in one individual
The resistant individual survives when treated with the antibiotic
The individual reproduces and passes on the resistance allele
This occurs over many generations until only resistant individuals remain
How does antibiotic use increase the probability that a resistant population of bacteria will arise?
Antibiotic use can increase the probability that a resistant population of bacteria will arise because the antibiotics kill any non-resistant individuals, meaning that any randomly occurring alleles for resistance become highly advantageous. The resistance alleles are therefore more likely to be passed on.
Why can infections caused by antibiotic resistant strains of bacteria be hard to control?
Infections caused by antibiotic resistant strains of bacteria can be hard to control because:
human immunity to new bacterial strains may be lower
the standard antibiotic treatments are ineffective
several different types of antibiotic may be needed to kill all the bacteria
True or False?
MRSA is an antibiotic resistant strain of bacteria.
True.
MRSA stands for methicillin resistant Staphylococcus aureus.
How can the the problem of antibiotic resistance be reduced?
The development of antibiotic resistance can be reduced by measures such as:
Using antibiotics only when necessary, e.g. not for minor illness or viral infections
Limiting antibiotic use in agriculture
Improve hygiene measures in hospitals so that resistant strains do not spread
Prescribing specific types of antibiotic for specific types of infection