10.3 Gene Pools and Speciation

Question 1

allele frequency

Answer 1

indicates the proportion of the different alleles in a population

Question 2

Mutation def.

Answer 2

spontaneous mutations can alter alleles frequencies and create new alleles. Mutations are random changes in the DNA code that may alter structures, functions and behaviour

Question 3

Gene flow def.

Answer 3

genes can flow into or out of gene pools as individuals move from one gene pool to another e.g. immigration and emigration

Question 4

Small population size

Answer 4

in small populations, allele frequencies can change randomly from generation to generation e.g. genetic drift, population bottleneck

Question 5

Sexual reproduction

Answer 5

Sexual reproduction can introduce new gene combinations and alter allele frequencies if mating is assortative

Question 6

Genetic drift

Answer 6

The change in the composition of a gene pool as a result of a chance or random event

Question 7

Natural selection affect on gene pool

Answer 7

The change in the composition of a gene pool as a result of differentially selective environmental pressures

Question 8

Reproductive isolating mechanisms

Answer 8

mechanisms that keep the new gene pool different from the original (prevents members of the same species from reproducing)

Question 9

Prezygotic mechanisms

Answer 9

isolating mechanisms that occur before fertilisation

Question 10

Geographical isolation

Answer 10

prezygotic
happens when physical barriers such as land or water prevent mating

Question 11

Ecological isolation

Answer 11

prezygotic
different populations may occupy different habitats within the same geographical area

Question 12

Behavioural isolation

Answer 12

prezygotic
occurs when two populations exhibit different specific courtship patterns

Question 13

Temporal isolation

Answer 13

prezygotic
occurs when two populations differ in their periods of activity or reproductive cycles

Question 14

Structural imcompatibility

Answer 14

prezygotic
occurs when physical structures prevent successful mating (e.g. incompatible copulatory apparatuses)

Question 15

Postzygotic mechanisms

Answer 15

mechanisms that act after fertlisation

Question 16

Hybrid inviability

Answer 16

postzygotic
hybrids are produced but fail to develop to reproductive maturity

Question 17

Hybrid sterility

Answer 17

postzygotic
hybrids fail to produce functional gametes

Question 18

Speciation

Answer 18

is the process by which a new species is formed by the splitting of an existing species, occurs when gene flow has ceased
two types:
allopatric and sympatric

Question 19

Allopatric speciation

Answer 19

Allopatric speciation occurs when a geographical barrier physically isolates populations of an ancestral species

The two populations begin to evolve separately as a result of cumulative mutation, genetic drift and natural selection
Eventually the two populations reach a degree of genetic divergence whereby they can no longer interbreed (speciation)

Question 20

Sympatric speciation

Answer 20

Sympatric speciation is divergence of species within the same geographical location (i.e. without a physical barrier)

Sympatric speciation may result from the reproductive isolation of two populations as a result of genetic abnormalities
Typically, a chromosomal error may arise which prevents successful reproduction with any organism lacking the same error

Question 21

Speciation in the genus Allium

Answer 21

The genus Allium is comprised of monocotyledonous flowering plants and includes onions, garlic, chives and leeks

In many of these species polyploidy has occurred, resulting in reproductively isolated populations with distinct phenotypes

Question 22

Gradualism

Answer 22

is the view that evolutionary changes occur slowly from one form to another over time

Question 23

Punctuated equilibrium

Answer 23

has long periods with no change and short periods of rapid evolution

Question 24

Stabilising selection

Answer 24

Where an intermediate phenotype is favoured at the expense of both phenotypic extremes
This results in the removal of extreme phenotypes (phenotypic distribution becomes centrally clustered to reflect homogeneity)
Operates when environmental conditions are stable and competition is low
An example of stabilising selection is human birth weights

Question 25

Directional selection

Answer 25

Where one phenotypic extreme is selected at the cost of the other phenotypic extreme
This causes the phenotypic distribution to clearly shift in one direction (towards the beneficial extreme)
Operates in response to gradual or sustained changes in environmental conditions
Directional selection will typically be followed by stabilising selection once an optimal phenotype has been normalised
An example of directional selection is the development of antibiotic resistance in bacterial populations

Question 26

Disruptive selection

Answer 26

Where both phenotypic extremes are favoured at the expense of the intermediate phenotypic ranges
This causes the phenotypic distribution to deviate from the centre and results in a bimodal spread
This occurs when fluctuating environmental conditions (e.g. seasons) favour the presence of two different phenotypes
Continued separation of phenotypic variants may eventually split the population into two distinct sub-populations (speciation)
An example of disruptive selection is the proliferation of black or white moths in regions of sharply contrasting colour extremes

Question 27

The founder effect

Answer 27

The founder effect occurs when a small group breaks away from a larger population to colonise a new territory

As this population subset does not have the same degree of diversity as a larger population, it is subject to more genetic drift
Consequently, as this new colony increases in size, its gene pool will no longer be representative of the original gene pool
The founder effect differs from population bottlenecks in that the original population remains largely intact

Question 28

Population bottleneck

Answer 28

Population bottlenecks occur when an event reduces population size by an order of magnitude (~ >50%)

These bottlenecks may result from natural occurrences (e.g. fires, floods, etc.) or be human induced (e.g. overhunting)
The surviving population has less genetic variability than before and will be subject to a higher level of genetic drift
As the surviving members begin to repopulate, the newly developing gene pool will be divergent to the original