Topic 6c - The Development of Understanding Genetics and Evolution Flashcards
What theory did Charles Darwin propose? Why?
Charles Darwin, as a result of observations on a round-the-world expedition, backed by years of experimentation and discussion and linked to developing knowledge of geology and fossils, proposed the theory of evolution by natural selection.
What does the theory of evolution by natural selection state? (4) - blurting / whiteboard
- individuals in a species show a wide range of variation caused by differences in genes
- individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
- alleles that code for advantageous characteristics are therefore passed to offspring at a higher rate than those that code for characteristics less suited to survival
- over many generations these beneficial characteristics become more common in the population and the species changes, or evolves
What is the theory of evolution by natural selection also known as?
Survival of the fittest
What is the term survival of the fittest used to describe?
It is a term used to explain why some organisms succeed in the competitive struggle for survival against other members of their population.
When and where did Charles Darwin publish his theories?
Darwin published his ideas in his famous book, On the Origin of Species (1859).
How does natural selection work with the example of snails? (5) - blurting / whiteboard
- Within the population of snails there is variation in shell colour => normal varieties of shell colours in this snail species are black or grey.
- Chance mutations lead to a small number of snails having a white shell.
- The white shelled snail(s) survive longer because they are better camouflaged and so are less likely to be seen by predators and eaten.
- As they survive longer they get more opportunities to reproduce and so the allele for white shells is passed onto offspring more frequently than the alleles for black or grey shells.
- Over generations this is repeated until the majority of snails in the population have white shells.
How does natural selection work with the example of peppered moths? (5) - blurting / whiteboard
- There is variation within the peppered moth population => more light moths than dark moths.
- Pollution leads to darker bark on trees. The environmental change is beneficial to the dark moths. They now have the ability to camouflage against the trees.
- Light moths are now more likely to be eaten by birds, and less likely to reproduce.
- Dark moths are now more likely to survive and reproduce, passing on their alleles for a dark phenotype to their offspring.
- Overtime there is a gradual increase in the proportion of dark moths => now more dark moths than light moths.
What is the general theory of natural selection that can be applied to unseen examples? (4)
- variation exists in a population due to mutation
- some individuals have advantageous alleles that increase their chance of survival
- surviving individuals are more likely to reproduce and pass on their alleles
- over time the advantageous alleles become more common in the population
Why was the theory of natural selection only gradually accepted? (5)
- There was much controversy surrounding these revolutionary new ideas.
- The theory challenged the idea that God made all the animals and plants that live on Earth.
- There was insufficient evidence at the time the theory was published to convince many scientists.
- The mechanism of inheritance and variation was not known until 50 years after the theory was published.
- The theory of evolution by natural selection developed over time and from information gathered by many scientists.
Was there another theory of evolution?
Another theory of evolution, developed at the start of the 19th century (before Darwin announced his theory), was that of French scientists Jean-Baptiste Lamarck.
What was Lamarck’s theory of evolution mainly based on?
Lamarck’s theory was based mainly on the idea that changes that occur in an organism during its lifetime can be inherited.
What two main ideas did Lamarck’s theory of evolution involve?
- a characteristic that is used frequently by an organism becomes better and stronger, whereas a characteristic that isn’t used gradually disappears
- the beneficial characteristics that are used frequently (and are improved as a result) are passed to offspring
How does Lamarck’s theory of evolution work using the example of giraffes? (3)
- Giraffes had a short-necked ancestor that would frequently stretch its neck to reach the high branches so it could feed on the leaves.
- This repeated stretching could very slowly elongate the giraffe’s neck and that this would be passed to the giraffe’s offspring.
- Over time and many generations, the giraffe would evolve to have the very long neck it has today.
Is Lamarck’s theory of evolution correct? How do we know?
We now know that in the vast majority of cases this type of inheritance cannot occur and that Lamarck’s ideas were incorrect.
Who is Alfred Russel Wallace and what did he do (briefly)?
Alfred Russel Wallace was a scientist who, after conducting his own travels around the world and gathering much evidence, independently developed his own theory of evolution based on the process of natural selection.
Did Wallace work with Darwin? How?
He published scientific papers on his theory with Darwin in 1858 (Darwin published his book, On the Origin of Species, the following year).
What is Wallace best known for? (2)
- His work studying the warning colouration of species (particularly butterflies) and how this must be an example of a beneficial characteristic that had evolved by natural selection, as the warning colouration helps to deter predators.
- Developing the theory of speciation.
How did we get our current understanding of speciation?
Alfred Wallace did much pioneering work on speciation but more evidence over time has led to our current understanding of the theory of speciation.
What is speciation?
Speciation is a process that results in the formation of a new species.
When do we say speciation has occurred?
When populations of the same species become so different that they are unable to interbreed and produce fertile offspring, they are considered different species and speciation has occurred.
What combines to allow speciation to happen?
Isolation and natural selection
How does speciation happen? (5) - blurting / whiteboard
- Populations of the same species can become isolated from one another due to the formation of a physical barrier (eg. a new river or mountain range) – this is known as geographic isolation.
- The environment will be different on either side of this physical barrier (eg. different climates or different food available).
- The environmental differences on either side will provide different selection pressures and natural selection will cause a different set of characteristics to become more common in the two isolated populations.
- Over many generations, individuals from the two populations will have become so distinct (genetically, behaviorally, physically) that they will no longer be able to interbreed and produce fertile offspring.
- The two populations are now separate species.
Who was Gregor Mendel? What did he do? (4)
- Gregor Mendel was an Austrian monk.
- He was trained in mathematics and natural history at the University of Vienna.
- In the mid-19th century, Mendel carried out breeding experiments on plants.
- He studied how characteristics were passed on between generations of plants.
What is an example of one of Gregor Mendel’s studies?
He conducted studies with pea plants and looked at how the height characteristic was inherited.
What was one of Mendel’s conclusions - broad?
One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged.
What did Mendel conclude from his pea plant height characteristic studies?
Mendel showed that height in pea plants was the result of separately inherited ‘hereditary units’ passed down from each parent plant to the offspring plants – this particular experiment showed that the ‘unit’ for tall plants (T) was dominant over the ‘unit’ for short plants (t).
What did Mendel’s work provide the foundations for?
Modern genetics
Why was the importance of Mendel’s discovery not recognised until after his death? (2)
- His studies were totally new to science in the 19th century.
- There was no knowledge of the mechanisms behind his findings (DNA, genes and chromosomes had not been discovered yet).
What was observed in the late 19th century and early 20th century?
the behaviour of chromosomes during cell division
What did scientists realise about chromosome behaviour and Mendel’s work? (3)
- Scientists realised that chromosomes behaved in a very similar way to Mendel’s ‘hereditary units’.
- Scientists believed Mendel’s ‘units’ must be located on chromosomes.
- We now know that this is true and call these ‘units’ genes.
What was discovered in the mid-20th century - following Mendel’s units and chromosome behaviours? What did this lead to the development of? (2)
- In the mid-20th century (1953) the structure of DNA was determined and the mechanism of gene function worked out.
- This scientific work by many scientists led to the gene theory being developed.
What is a very clear piece of evidence for the theory of evolution?
antibiotic resistance in bacteria
What is an antibiotic?
An antibiotic is a chemical that can kill or inhibit the growth and reproduction of bacteria.
How are antibiotics useful?
Antibiotics are extremely useful to humans as some bacteria are pathogenic and can cause life-threatening disease.
How often do Bacteria reproduce? What does this mean for evolution?
Bacteria reproduce, on average, every 20 minutes and therefore evolution occurs in a much shorter time span.
How is antibiotic resistant bacteria evidence for evolution? (6) - blurting / whiteboard
- Like all other organisms, within a population, there will be variation caused by mutations.
- A chance mutation might cause some bacteria to become resistant to an antibiotic (eg penicillin).
- When the population is treated with this antibiotic, the resistant bacteria do not die.
- This means they can continue to reproduce with less competition from non-resistant bacteria, which are now dead.
- Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation.
- Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment.
How have humans helped develop the evolution of antibiotic resistant bacteria?
Through overuse of antibiotics.
What are 3 examples of antibiotic overuse?
- For the treatment of non-serious infections.
- Routine treatment to animals in agriculture.
- Failure to finish the prescribed course of antibiotics.
What can increases in the population of antibiotic-resistant bacteria cause? Why?
Increases in the population of antibiotic-resistant bacteria cause infections and diseases which are harder to control as it is difficult to find antibiotics that certain strains of bacteria are not resistant to.
What is an example of a hard to treat bacteria due to it being antibiotic resistant?
An example is MRSA, a very dangerous bacterial strain that is resistant to most antibiotics. If someone gets infected with MRSA they cannot be treated easily.
What is the increase we are currently seeing in antibiotic resistance is encouraging?
The increase we are currently seeing in antibiotic resistance is encouraging drug companies to develop new antibiotics that are effective against these new resistant strains, such as MRSA.
Why has the problem of antibiotic resistance not been solved by developing new antibiotics that are more effective? (3)
- The number of new antibiotics discovered has slowed significantly.
- Developing new antibiotics is also a very costly process.
- Some scientists are worried we may not be able to keep up with the demand for new antibiotics, as more and more antibiotic-resistant strains evolve.
How can the rate of development of antibiotic resistant strains be reduced? (3)
- Doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections.
- Patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains.
- The agricultural use of antibiotics should be restricted.
Why is Darwin’s theory of evolution now widely accepted? (3)
- Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes.
- Our understanding of genetics has made clear the mechanism by which natural selection can occur.
- There is further evidence for evolution in the fossil record and our knowledge of how resistance to antibiotics evolves in bacteria.
What are fossils?
Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks.
What are 3 ways fossils might be formed?
- From parts of organisms that have not decayed because one or more of the conditions needed for decay are absent.
- When parts of the organism are replaced by minerals as they decay.
- As preserved traces of organisms, such as footprints, burrows and rootlet traces.
Why are there gaps in the fossil record? What do gaps in the fossil record mean for scientists? (3)
- Many early forms of life were soft-bodied, which means that they have left few traces behind – soft tissues often decay fully, leaving no trace in the fossil record.
- What traces there were have been mainly destroyed by geological activity (eg. tectonic plate movements may have crushed fossils that had already formed).
- This is why scientists cannot be certain about how life began on Earth.
What can we learn from fossils?
We can learn from fossils how much or how little different organisms have changed as life developed on Earth.
What is extinction/ when is it said to have occurred?
Extinctions occur when there are no remaining individuals of a species still alive.
How do species become extinct (simple)? (2)
- Species that are poorly adapted to their environment are less likely to survive and reproduce compared to species that are well adapted to their environment.
- If they are unable to survive and reproduce sufficiently to maintain their population numbers they will eventually go extinct.
What are 5 factors that can lead to extinction?
- New diseases
- New predators
- New better adapted, and more successful competitors
- Changes to the environment over geological time
- Single catastrophic events
How can new diseases lead to extinction? (2)
- A species that has previously not had to evolve resistance to a particular disease or pathogen may not have any resistant alleles within its population.
- This will lead to very large numbers of the species dying very quickly and the species may not have time to develop immunity to the new disease before it is wiped out completely.
How can new predators lead to extinction? (2)
- A species that has previously not had to evolve defence mechanisms (eg. camouflage, horns, poison etc) to a particular predator will be very vulnerable if the new predator appears.
- This will lead to the species being heavily predated and the species may not have time to adapt (by developing new defence mechanisms)
before it is wiped out completely.
How can new better adapted, and more successful competitors lead to extinction? (3)
- A species will have to compete for resources (eg. food) if a new competitor species appears that requires the same resources.
- If a new competitor species is better adapted to take advantage of these resources, then it will out-compete the original species.
- This may eventually lead to the original species being wiped out completely.
How can changes to the environment over geological time lead to extinction? (3)
- If a change in the environment occurs, a species may not be well adapted to this change and may be wiped out as a result.
- An example of such a change is climate change.
- For example, as global temperatures rise, certain species may not be able to survive at these higher temperatures and may eventually go extinct.
How can single catastrophic events lead to extinction? (3)
- Certain events may be catastrophic enough to wipe out entire ecosystems or habitats and therefore the species that live there as well.
- This is especially likely to occur if the species has a limited range (the area where it lives) close to where the event occurs.
- Examples include asteroid collisions with Earth and massive volcanic eruptions.
