Populations And Evolution

Question 1

What is gene pool?

Answer 1

• the sum total of all the different genes in the population (all alleles)

Question 2

What is the allele frequency?

Answer 2

• how many times the allele appears in the gene pool

Question 3

What are the assumptions of the Hardy-Weinberg principle?

Answer 3

• the populations are large
• there is no movement of organisms into or out of the population
• there is random mating between individuals in the population
• all genotypes must have the same reproductive success; ie there is no selection for or against a particular genotype
• there is no genetic mutation

Question 4

What is the Hardy-Weinberg equation?

Answer 4

p2 + 2pq + q2 = 1
p + q = 1

p = dominant allele
q = recessive allele
p2 = AA
q2 = aa
2pq = Aa

Question 5

What is variation due to genetic factors?

Answer 5

• caused by gene mutation
• crossing over in 1st meiotic division (different combos of genes)
• independent assortment
• random fertilisation

Question 6

What is variation due to environmental factors?

Answer 6

• e.g. diet, infectious disease, climate, light intensity

Question 7

What is the role of variation in natural selection?

Answer 7

• a description of how the organisms vary
• explain how genetic mutations produced this genetic variation
• explain which individuals are at a selective advantage
• organisms with a selective advantage will survive, reproduce and pass on their alleles (differential reproductive success)
• how this will alter the frequency of alleles in the population

Question 8

Why are offspring overproduced?

Answer 8

• more than needed to sustain population
• allows for some to die

Question 9

What is stabilising selection?

Answer 9

• environmental conditions remain the same
• means are favoured, extremes are fought against
• eliminates extremes

Question 10

What is directional selection?

Answer 10

• environmental conditions change so phenotype needed to survive is favoured
• new individuals become more adapted to survive at one end of the spectrum and so over time the mean changes to suit the new phenotype
• this results in phenotypes at one extreme being favoured and the other being favoured against

Question 11

What is disruptive selection?

Answer 11

• environmental conditions have two distinct forms
• favours individuals with extreme phenotypes
• eliminates phenotypes around the mean

Question 12

How are new species formed?

Answer 12

• offspring overproduce (more than needed to sustain population
• all offspring show variation
• some variations better adapted to environment (environmental resources are limited)
• pass an advantageous allele to offspring
• allele becomes more dominant/frequent in the population than previous advantageous allele
• species changes and evolves

Question 13

What is allopatric speciation?

Answer 13

• geographical isolation
• variation due to mutation
• different selection pressures such as environment
• differential reproductive success, organisms with a selective advantage survive and reproduce
• this leads to a change in allele frequency over time

Question 14

What is sympatric speciation?

Answer 14

• isolating mechanisms
• variation due to mutation
• different selection pressures
• differential reproductive success, organisms with a selective advantage survive and reproduce
• this leads to a change in allele frequency over time

Question 15

What are isolation mechanisms?

Answer 15

• temporal (different breeding seasons, different times of day or year)
• hybrid sterility (offspring are produced but are sterile)
• ecological (organisms may occupy different habitats within the same location)
• gamete mortality (sperm fails to reach or penetrate egg)
• behavioural (different mating rituals)
• structural (sexual organs of organisms are not compatible)

Question 16

What is a species?

Answer 16

• A group of organisms with similar morphological and physiological features that able to breed together and produce fertile offspring

Question 17

Using this information, suggest how these two species of palm tree arose by sympatric speciation. (mark scheme answer 5 marks)

Answer 17

1. Occurs in the same habitat/environment/population;
2. Mutation/s cause different flowering times;
3. Reproductive separation/isolation
   OR
   No gene flow
   OR
   Gene pools remain separate;
4. Different allele/s passed on/selected
   OR
   Change in frequency of allele/s;
5. Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed