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)