evolution may lead to speciation

Question 1

what is a phenotype?

Answer 1

appearance of a characteristic due to both the genetic constitution of the organisms and due to environmental factors

Question 2

what are selection pressures?

Answer 2

Environmental factors that limit the population of a species. they include predation, competition and disease.

Question 3

describe stabilising selection

Answer 3

· Occurs in all populations where environment is stable.
· Selective pressure at both ends of distribution.
· The intermediate phenotype is selected for, and the extreme phenotypes are selected against
· Reduces variability, the size of the range within population.
· Reduces opportunity for evolutionary change.
· Reduces the range of possible characteristics in the population
e.g. birth mass in humans

Question 4

describe directional selection

Answer 4

• Mean in population represents optimum for existing conditions
• Environmental change may produce new selection pressure that favours an extreme phenotype, as when conditions change, phenotypes necessary for survival also change
• Some organisms, due to mutation, will posess an allele which gives them an advantage in the new environment, and they are selected for
• Those that don’t have the favourable allele will be selected against
• Over time selection means these will predominate and the mean will shift.
  e.g. antibiotic resistance in bacteria

Question 5

describe disruptive selection

Answer 5

• Both extremes of the phenotype are selected for, and the mean is selected against
• An example of disruptive selection: Changes in environmental temperature and fur length of an animal. Temperatures may alternate from 5oC in winter to 15oC in the summer. The colder winter temperatures favour animals with long fur, and the warmer summer temperature favour animals with short fur.
• Could lead to speciation – one species has long fur and is active in winter, the other short fur and active in summer

Question 6

what is evolution?

Answer 6

Evolution by natural selection is a change in the allele frequencies in a population.

Question 7

what is speciation?

Answer 7

Speciation: the development of new species from an existing species. It occurs when populations of the same species have separate gene pools, so they cannot interbreed to produce fertile offspring.

Question 8

define allopatric speciation + describe it

Answer 8

Allopatric Speciation: when 2 populations of the same species become geographically isolated from each other, caused by a physical barrier between the 2 populations e.g. river, separating their gene pools.
* Geographical isolation occurs, there may be different abiotic conditions in the 2 different areas.
* Within each population mutations have already formed advantageous alleles to the selection pressures.
* Those organisms with the alleles which give them a selective advantage in the environment can survive and reproduce, creating more offspring and passing their favourable alleles onto the offspring.
* Over many generations, the allele frequencies in each population will change.
* Over a long period of time, the populations will be so genetically different they will be unable to interbreed to produce fertile offspring.

Question 9

describe sympatric speciation

Answer 9

• Sympatric speciation occurs within the same environment/habitat/population – there is no geographical isolation
• By chance some organisms have mutations which give them different alleles to other individuals in the population making them reproductively isolated. (GIVE ALLELE IN ANSWER)
• This separates their gene pools.
• When the organisms reproduce, different alleles will be passed on to offspring
• Over a long period of time the organisms will be so genetically different that they will no longer be able to interbreed to produce fertile offspring
  This is disruptive selection.

Question 10

why is genetic drift important + how is it different to natural selection?

Answer 10

In small populations, genetic drift is important in causing changes in allele frequency.
* Small populations have a small gene pool (smaller variety
of alleles), and BY CHANCE one allele may be inherited more often and become more frequent in the population than another allele.
Natural selection, however, CAUSES alleles to become more frequent if they increase an organism’s survival chances.

Question 11

what is a phylogenetic hierarchy?

Answer 11

Phylogenetic – shows evolutionary relationships
Hierarchy – groups within larger groups, with no overlap between groups