Selection And Speciation- Paper 2

Question 1

What are the 3 causes of variations?

Answer 1

1. Mutations- causes combination of new alleles which may cause a new phenotype
2. Meiosis- caused by independent segregation and crossing over
3. Random fertilisation and fusion of Gametes during sexual reproduction

Question 2

What are features of variation which is caused by genet factors?

Answer 2

It is discontinuous, which produces categoric data and is usually caused by a single gene.

Question 3

What could a mutation be?

Answer 3

A selective advantage
Neutral as the code is degenerate
A selective disadvantage, inhibits gene and selects against advantageous alleles

Question 4

What are environmental influences

Answer 4

Abiotic and biotic factors, the environment influences the organism’s phenotype and the way the genes are expressed

Question 5

Define natural selection

Answer 5

A process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population

Question 6

What determines the spread of an allele within the gene pool

Answer 6

Selection pressures, they are either abiotic or biotic

Question 7

Stabilising selection

Answer 7

Occurs in populations where the environment is stable
Selection pressures at both ends of distribution
Favours the average
Tends to eliminate extremes
Reduces variability, the size of the range within population
Reduces opportunity for evolutionary change

Question 8

Directional selection

Answer 8

Mean in population represents optimum phenotype for existing conditions
Environmental change may produce new selection pressures that favour an extreme phenotype
Changed conditions, favour allele combination necessary for survival
Some organisms will possess the new optimum phenotype
Over time selection means this allele combination will predominate and the mean phenotype will shift

Question 9

Disruptive selection

Answer 9

Environment has selective pressures that favour two extreme phenotypes
When conditions change the optimum phenotypes necessary for survival will also change
Some organisms will possess the new extreme optimum phenotypes
Over time selection of these two extremes will dominate and the mean will shift in both directions

Question 10

Species definition and facts

Answer 10

The evolution of a new species from an existing species
Species belong in the same gene pool
Two populations must undergo a period of reproductive isolation to become genetically distinct through an accumulation of mutations and different selection pressures

Question 11

Genetic drift description

Answer 11

Random increase or decrease in allelic frequency, important in small populations where the loss will result in significant change to the frequency. May occur from natural disasters such as volcanic eruption

Question 12

gene flow description

Answer 12

Change in allelic frequency due to the migration of fertile individuals, such as migration

Question 13

Allopatric speciation

Answer 13

Geographical isolation- a physical barrier divides a population. Each population may be subjected to different selective pressures,mutations accumulate, change in genotype and phenotype , reproductively isolated, each population has become separate species with its own gene pool

Question 14

Sympatric selection

Answer 14

Organisms in same area become reproductively separated either from choice of food or choice of season to mate in or become active after hibernation.

Question 15

Other isolating mechanisms: temporal

Answer 15

Organisms breed at different times of the year

Question 16

Other isolating mechanisms: Ecological

Answer 16

Different habitats within same area

Question 17

Other isolating mechanisms: Behavioural

Answer 17

Different behaviour patterns eg courtship behaviour

Question 18

Other isolating mechanisms: mechanical

Answer 18

Anatomical differences making it impossible for games to come together

Question 19

Other isolating mechanisms: gametic

Answer 19

Incompatibility between gametes prevent hybrid from forming

Question 20

Other isolating mechanisms: hybrid

Answer 20

Organisms interbreed but offspring are infertile

Question 21

Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. this led to the formation of a number of different species of pupfish. Explain how these different species evolved

Answer 21

Geographical isolation
Separate gene pools
Variation due to mutation
Different environmental pressures
Selection for advantageous allele
Differential reproductive success
Leads to change in allele frequency
Occurs over a long period of time

Question 22

It has been suggested that a new species of grass may evolve on soil that has been polluted with copper. explain how this new species may evolve

Answer 22

Variation caused by mutation
Some plants have allele to survive
Differential reproductive success
Increase in frequency of advantageous allele
Not interbreeding with other populations

Question 23

using this information, suggest how these two species of palm tree arose by sympatric speciation

Answer 23

Occurs in same habitat
Mutations cause different flowering times
Reproductive isolation, gene pools remain separate
Change in allele frequency
Disruptive natural selection
Eventually different species cannot interbreed to produce fertile offspring

Question 24

Guppies with large brains are better at identifying predators. The scientist found that only female guppies with large brains were attracted to male guppies bright in colour

Answer 24

females mate with males bright in colour, offspring will be bright in colour so will attract larger brained females , more reproduction of fish with larger brained females, population are better at identifying predators

Question 25

Explain how different subspecies of giraffe may have evolved from a common ancestor

Answer 25

No interbreeding, gene pools are separate
Mutation linked to different markings
Selection linked to markings
Adapted organisms breed
Change in allele frequency

Question 26

Describe how you could use the mark-release-recapture method

Answer 26

Capture, mark and release
Method of marking does not harm organism
Leave sufficient time for lizards to randomly distribute before collecting a second sample
Population= number in first sample x number in second sample/ number recaptured