AOS 1 exam questions

Question 1

What are the differences between allopatric speciation and sympatric speciation?

Answer 1

• 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

Question 2

What are the similarities between allopatric speciation and sympatric speciation?

Answer 2

• 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

Question 3

What are index fossils?

Answer 3

.

Question 4

Why might a cactus not undergo fossilisation?

Answer 4

• 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

Question 5

What is convergent evolution?

Answer 5

When two non-related species have evolved similar adaptions due to similar environmental conditions in different regions.

Question 6

Provide an example of convergent evolution.

Answer 6

Sharks and dolphins both have fins and sharp teeth despite shark being a marine carnivore.

Question 7

What is the founder effect?

Answer 7

Occurs when a new population is established by a very small number of individuals which come from a larger population.

Question 8

What features does a small population have as a result of the founder effect?

Answer 8

• reduced variation from original population

- non- random sample of genes in orignal population

Question 9

How can two species evolve? (4)

Answer 9

1. one group becomes isolated by changed geography
2. geneflow is no longer possible
3. allele frequencies change due to natural selection as groups are acted upon by different selection pressures
4. eventually species are different enough that they can no longer produce viable/ fertile offspring

Question 10

How can you establish whether two species are different?

Answer 10

Interbreed two groups and if they produce viable and fertile offspring, they are distinct species.

Question 11

Explain the process of natural selection.

Answer 11

• 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

Question 12

Two conditions that determine whether something is an example of selective breeding.

Answer 12

• presence of selective agent

- presence of selected/ desired phenotype

Question 13

Does gene flow or a selective agent act more quickly on allele frequencies?

Answer 13

• geneflow has immediate action: taking effect as soon as group migrates into population
• selective pressure occurs over one or more generations

Question 14

Why is diversity an advantage?

Answer 14

Diversity produces a variety of phenotypes. There will be an increased chance of survival of population if environment changes.

Question 15

Why might different species be similar?

Answer 15

• 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

Question 16

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

Answer 16

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

Question 17

What is genetic drift?

Answer 17

The change in allele frequencies of a population due to chance.
Evident in small isolated populations.

Question 18

What is selective breeding?

Answer 18

The deliberate process of chosing species to breed based on the desired phenotypic features they display.

Question 19

What are the disadvantages of selective breeding?

Answer 19

• results in less variation: meaning theres a higher chance that all population will be affected by an environmental change

Question 20

Define evolution.

Answer 20

Any change in the heritable traits within a population across generations.

Question 21

What is gene flow?

Answer 21

Transfer of genetic information from one population to another, resulting in a change in allele frequencies.

Question 22

How does gene flow impact allele frequencies?

Answer 22

Immigrant group has different allele frequencies, so this gene flow causes a change in allele frequencies in new population.

Question 23

How does artificial insemination interfere with the natural evolutionary process?

Answer 23

• 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

Question 24

How new and old species became separate?

Answer 24

• 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

Question 25

How chromosome differences result in reproductive isolation?

Answer 25

- 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

Question 26

What is divergent evolution?

Answer 26

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.

Question 27

Why might a species be found in a particular area?

Answer 27

- hunted to extinction by humans | - outcompeted by competitor

Question 28

What is the difference between absolute age and relative age?

Answer 28

Absolute age: expressed in time units | Relative age: expressed simply as older/ younger/ same age as another rock layer

Question 29

What assumptions can be made about rock strata?

Answer 29

- strata near the top are more recent | - strata have been laid down in chronological order

Question 30

What comparative embryology?

Answer 30

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

Question 31

What is continental drift?

Answer 31

Refers to movement of the continents over the earth's surface through geological time.

Question 32

What is speciation?

Answer 32

process of formation of new species.

Question 33

What are the pre-mating isolation mechanisms?

Answer 33

Mechanisms that operate in nature to prevent the mating of members of two different species.

Question 34

What examples of pre-mating isolation mechanisms? (4)

Answer 34

- 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

Question 35

What are the post-mating isolation mechanisms?

Answer 35

Mechanisms that operate after members of two different species have mated that prevent the production of viable fertile offspring.

Question 36

What examples of post-mating isolation mechanisms? (4)

Answer 36

- 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.

Question 37

What are subspecies?

Answer 37

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.

Question 38

What are the two forms of speciation?

Answer 38

- allopatric | - sympatric