Selection & Speciation

Question 1

Causes of variation (sexual reproduction)

Answer 1

• primary source of genetic variation = mutation
• meiosis
• random fertilisation / fusion of gametes

Question 2

Name 3 environmental influences

Answer 2

• temperature
• light intensity
• humidity

Question 3

Define natural selection

Answer 3

• process which organisms 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 4

Describe stabilising selection

Answer 4

• occurs in all populations where environment is stable
• selection pressure at both ends of distribution
• favours the average
• tends to eliminate extremes
• reduced variability, size of range within population
• reduces opportunity for evolutionary change

Question 5

Describe directional selection

Answer 5

• mean in population represents optimum phenotype for existing conditions
• environmental change may produce new selection pressure that favours extreme phenotype
• some organisms will possess the new optimum phenotype
• over time selection means this allele combination will predominate and mean phenotype will shift

Question 6

Describe disruptive selection

Answer 6

• opposite of stabilising
• environment has selection pressures that favours 2 extreme phenotypes
• when conditions change optimum phenotypes necessary for survival will also change
• some organisms will possess the new extreme phenotypes
• overtime selection means these 2 extremes will dominate and mean will shift both directions
• least common selection

Question 7

Define allopatric speciation

Answer 7

• physical barrier divides population preventing interbreeding
• isolated population maybe subject to different selection pressures
• mutations accumulate
• changes in geno and phenotypes
• when two population re unite so different unable to interbreed
• each become separate species w own gene pool

Question 8

Describe sympatric speciation

Answer 8

• means “same country”
• requires organism in same area to become reproductively separated for other reasons
• choice of good or choice of season to mate in or become active after hibernation

Question 9

Describe temporal isolation

Answer 9

• organisms breed at different times of year

Question 10

Describe ecological isolation

Answer 10

• different habitats within same area

Question 11

Describe behavioural isolation

Answer 11

• different behaviour patterns

Question 12

Describe mechanical isolation

Answer 12

• anatomical differences making it impossible for gametes to come together

Question 13

Describe gametic isolation

Answer 13

• incompatibility between gametes prevent hybrid from forming

Question 14

Describe hybrid isolation

Answer 14

• organisms interbreed but offspring are infertile

Question 15

Describe speciation

Answer 15

• the evolution of a new species from existing species
• group of Individuals with similar characteristics and same genes capable of interbreeding to produce fertile offspring
• belong to the same gene pool