Chapter 23 ( Evolutions of Populations)

Question 1

What is a gene pool?

Answer 1

All genes in a population, including all alleles and their frequencies.
Mnemonic: Pool of genes = ‘Gene Pool Party’.

Question 2

Define Hardy-Weinberg Equilibrium.

Answer 2

A population where allele frequencies remain constant if no evolutionary forces act.
Mnemonic: ‘Hardy-Weird things don’t happen’ unless drift, flow, mutation, nonrandom mating, or selection occur.

Question 3

List the 5 conditions for Hardy-Weinberg Equilibrium.

Answer 3

1. Very large population
2. No migration
3. No mutation
4. Random mating
5. No natural selection
   Trick: ‘Large Isolated Mutants Mate Randomly, Select Nothing’.

Question 4

What is genetic drift?

Answer 4

Random changes in allele frequencies in small populations.
Mnemonic: ‘Small drift, big shift’.
Example: Bottleneck effect & Founder effect.

Question 5

Explain the bottleneck effect.

Answer 5

Drastic reduction in population size alters gene frequencies.
Example: Earthquakes reducing genetic diversity.
Mnemonic: ‘Bottleneck squeezes out variety’.

Question 6

Explain the founder effect.

Answer 6

A few individuals colonize a new area, leading to a different gene pool.
Mnemonic: ‘Founders = Fresh gene soup’.

Question 7

What is gene flow?

Answer 7

Movement of alleles between populations via migration.
Example: Human global movement.
Mnemonic: ‘Genes Go with the Flow’.

Question 8

Define polymorphism.

Answer 8

Coexistence of 2+ forms (phenotypes) in a population.
Example: Snail shell colors, human blood types.
Mnemonic: ‘Poly = Many forms’.

Question 9

What is balanced polymorphism?

Answer 9

Maintained variation where multiple forms are favored depending on conditions.
Example: Peppered moths, Snow geese morphs.
Mnemonic: ‘Balance keeps diversity alive’.

Question 10

What is stabilizing selection?

Answer 10

Favors intermediate phenotypes, reduces extremes.
Example: Birds of average size surviving storms.
Mnemonic: ‘Stable center wins’.

Question 11

What is directional selection?

Answer 11

Favors one extreme phenotype, shifting average over time.
Mnemonic: ‘Direction = One side wins’.
Example: Pesticide resistance in insects.

Question 12

What is disruptive selection?

Answer 12

Favors both extreme phenotypes, average is selected against.
Mnemonic: ‘Disrupt = Divide population’.
Example: Bimodal shell patterns in snails.