AOS 1 exam questions Flashcards
What are the differences between allopatric speciation and sympatric speciation?
- A: physical isolation by geological barrier
- A: involves natural selection
- A: speed of emergence is slow
- S: occurs when individuals in the same habitat are reproductively isolated
- S: involves polyploidy
- S: speed of emergence is fast
What are the similarities between allopatric speciation and sympatric speciation?
- both occur through reproductive isolation of individuals
- both processes involve evolving a new, distinct species
- new species are incapable of interbreeding with pre-existing species
What are index fossils?
.
Why might a cactus not undergo fossilisation?
- low availability of water to develop sedimentary deposits which are associated with deposition of organisms that become fossils
- cactus do not have hard parts which are more likely tp become fossils
What is convergent evolution?
When two non-related species have evolved similar adaptions due to similar environmental conditions in different regions.
Provide an example of convergent evolution.
Sharks and dolphins both have fins and sharp teeth despite shark being a marine carnivore.
What is the founder effect?
Occurs when a new population is established by a very small number of individuals which come from a larger population.
What features does a small population have as a result of the founder effect?
- reduced variation from original population
- non- random sample of genes in orignal population
How can two species evolve? (4)
- one group becomes isolated by changed geography
- geneflow is no longer possible
- allele frequencies change due to natural selection as groups are acted upon by different selection pressures
- eventually species are different enough that they can no longer produce viable/ fertile offspring
How can you establish whether two species are different?
Interbreed two groups and if they produce viable and fertile offspring, they are distinct species.
Explain the process of natural selection.
- variation occurs in original population: acts as selective advantage
- selective pressure results in some species being more suited to environment due to certain phenotypic trait
- species with selective advantage survive, reproduce and pass one allele to next generation
Two conditions that determine whether something is an example of selective breeding.
- presence of selective agent
- presence of selected/ desired phenotype
Does gene flow or a selective agent act more quickly on allele frequencies?
- geneflow has immediate action: taking effect as soon as group migrates into population
- selective pressure occurs over one or more generations
Why is diversity an advantage?
Diversity produces a variety of phenotypes. There will be an increased chance of survival of population if environment changes.
Why might different species be similar?
- gene flow or interbreeding has occurred: due to living in close proximity
- there has been a recent isolating mechanism: meaning species have recently been isolated
Identify a change that:
a) would be in a closed population:
b) has its greatest impact on small populations
c) can act on both small and large populations
a) would be in a closed population: gene flow
b) has its greatest impact on small populations: genetic drift
c) can act on both small and large populations: selection pressure
What is genetic drift?
The change in allele frequencies of a population due to chance.
Evident in small isolated populations.
What is selective breeding?
The deliberate process of chosing species to breed based on the desired phenotypic features they display.
What are the disadvantages of selective breeding?
- results in less variation: meaning theres a higher chance that all population will be affected by an environmental change
Define evolution.
Any change in the heritable traits within a population across generations.
What is gene flow?
Transfer of genetic information from one population to another, resulting in a change in allele frequencies.
How does gene flow impact allele frequencies?
Immigrant group has different allele frequencies, so this gene flow causes a change in allele frequencies in new population.
How does artificial insemination interfere with the natural evolutionary process?
- restricts transmission of genes to the next generation as only very few ‘studs’ are used.
- the gene pool of the next generation will be less diverse with less genetic variation
- reduction in genetic variability leads to potential loss of alleles from gene pool
How new and old species became separate?
- two populations become seperate
- natural selection occurred: involving different selective agents acting on each species resulting in a change in allele frequencies
- individuals in 2 different species are unable to produce viable/ fertile offspring
How chromosome differences result in reproductive isolation?
- chromomsomes are no longer homologous, hence do not pair in meiosis
- no gamates are produced or viable offspring since offspring will have not have a normal number of chromosomes
What is divergent evolution?
Overtime, one ancestral species changes to give rise to several new species occupying a different niche.
The result of this evolution is at least one new species.
Why might a species be found in a particular area?
- hunted to extinction by humans
- outcompeted by competitor
What is the difference between absolute age and relative age?
Absolute age: expressed in time units
Relative age: expressed simply as older/ younger/ same age as another rock layer
What assumptions can be made about rock strata?
- strata near the top are more recent
- strata have been laid down in chronological order
What comparative embryology?
Proposes the idea that some species show similar structures in their early development but become more different over time.
Eg. share structures of gill slits and formation of tail
What is continental drift?
Refers to movement of the continents over the earth’s surface through geological time.
What is speciation?
process of formation of new species.
What are the pre-mating isolation mechanisms?
Mechanisms that operate in nature to prevent the mating of members of two different species.
What examples of pre-mating isolation mechanisms? (4)
- Isolation in time: species may be active by day and other species active at night: unlikely to meet
- Isolation in space: one species may live on mountain tops and the second in valleys: unlikely to meet
- Isolation by behaviour: one species does not recognise the signs of sexual readiness in a second species or is unable to perform the correct courtship rituals
- Isolation by anatomy: mating unsuccessful because of physical differences
What are the post-mating isolation mechanisms?
Mechanisms that operate after members of two different species have mated that prevent the production of viable fertile offspring.
What examples of post-mating isolation mechanisms? (4)
- Incompatibility of gametes: sperm cannot penetrate the outer coats surrounding the egg of the second species
- Zygote mortality: fertilisation occurs, but the zygote fails to develop.
- Inviability of zygote: zygote develops into an embryo but does not develop beyond that.
- Sterility of hybrid: hybrid offspring survive, but are sterile.
What are subspecies?
Before becoming different species, separated populations may be identified as distinct subspecies. At this stage, members of geographically separated populations are recognisably different from each other. However, if the populations come together again, members of the different subspecies groups can still interbreed and produce viable and fertile offspring.
What are the two forms of speciation?
- allopatric
- sympatric
