Biology- Evolution with and without selection

Question 1

Evolution occurs when….

Answer 1

natural selection acts on the genetic variability within a population
Environment favors certain individuals over others (those better suited to environment)

Question 2

HARDY-WEINBERG PRINCIPLE

Answer 2

– in large populations, if only random chance is at work, allele frequencies should remain constant (e.g. no evolution should occur, gene pool unchanged)

Question 3

H-W EQUILIBRIUM

Answer 3

• constant gene pool

- Is RARE!

Question 4

5 conditions that can cause allele frequencies to change, causes what to occur?

Answer 4

5 conditions can cause allele frequencies to change, causing evolution to occur (more than random chance) disrupts H-W equilibrium (at least one of these conditions is likely active in wild populations)

Question 5

5 conditions

Answer 5

1. Natural selection – some alleles favoured over others
2. Sexual selection – non-random mating
3. Mutation – introduces new alleles
4. Small population size – increases chance of genetic drift
5. Introduction or loss of genes – through immigration/emigration or horizontal gene transfer (gaining genes from different species)

Question 6

Patterns of selection:

- Selective Pressure

Answer 6

factors that affect the success of individuals (e.g. limited resources – food, water, space, mates, and threats – predators, disease, poor weather)

Question 7

Patterns of selection:

- Directional Selection

Answer 7

selection favours individuals with a more extreme variation of a trait (shifts away from the average)
E.g. hummingbird bill length based on length of flowers – new habitat with longer flowers

Question 8

Patterns of selection:

- Stabilizing Selection

Answer 8

selection favours individuals with the average phenotype
E.g. hummingbird’s environment is unchanging with medium length flowers (harder to sustain large bill, harder to eat with short bill), human birth weight

Question 9

Patterns of selection:

- Disruptive Selection

Answer 9

selection favours individuals with variations at opposite extremes of a trait over the intermediate phenotypes
E.g. two different sized flowers, neither favours a medium bill

Question 10

Patterns of selection:

- Sexual Selection

Answer 10

selection favours traits or variations that enhance the mating success of an individual  leads to sexual dimorphism (differing appearance of males and females), and mating and courtship behaviours
- E.g. female mate choice (based on behaviours or appearance) or male-versus-male competition (body size, antlers, fights for territory)

Question 11

Costs of Sexual Selection

Answer 11

(injury, death, malnutrition) to sexual selection  features may increase risk of predation (bright feathers, mating calls), and nutritional cost of maintenance of some features (e.g. antlers)

Question 12

Evolutionary change without selection:

- Genetic Drift

Answer 12

changes to allele frequency due to chance (much more significant in small populations) – can cause the frequency of an allele to increase or decrease dramatically, are two types:

Question 13

Evolutionary change without selection:

- Bottleneck Effect

Answer 13

population is dramatically, and often temporarily, reduced due to natural events or human activity

• After reduction, many of alleles found in larger population may have been lost, or significantly decreased. If population recovers, new generations will contain a limited variety of alleles (limited diversity increased vulnerability to disease)
• E.g. cheetahs reduced to as few as 12, 10,000 years ago

Question 14

Evolutionary change without selection:

- Founder Effect

Answer 14

small number of individuals separate from their original population to form a new population
- E.g. development of new species, e.g. on Galapagos

Question 15

Density Dependent Factors

Answer 15

Predators
Availability of resources
Nutrients supply
Disease/ pathogenic spread 
Accumulation of wastes

Question 16

Density Independent Factors

Answer 16

Phenomena (e.g. natural selection)
Abiotic factors (e.g. temperature, CO2 levels)
Weather conditions (e.g. floods, storms)