Unit 2: Key Area 2 - Evolution

Question 1

What is evolution

Answer 1

Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits

Question 2

Describe the process of evolution

Answer 2

During evolution, changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift

Question 3

What does natural selection act on and how does it arise

Answer 3

Natural selection acts on genetic variation in populations. Variation in traits arises as a result of mutation.

Question 4

Describe how mutations give rise to genetic variation

Answer 4

Mutation is the original source of new sequences of DNA. These new sequences can be novel alleles. Most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual.

Question 5

What happens during natural selection

Answer 5

During natural selection, the populations produce more offspring than the environment can support

Question 6

Describe the process of natural selection

Answer 6

Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation

Question 7

What does selection result in

Answer 7

Selection results in the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.

Question 8

Describe sexual selection

Answer 8

Sexual selection is the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring

Question 9

What may sexual selection lead to

Answer 9

Sexual selection may lead to sexual dimorphism

Question 10

What can sexual selection be a result of

Answer 10

Sexual selection can be due to male-male rivalry and female choice

Question 11

Describe male to male rivalry

Answer 11

Male-male rivalry involves large size or weaponry. Increases access to females through conflict.

Question 12

What is sexual dimorphism

Answer 12

Sexual dimorphism is when the male and female of a species look different

Question 13

Describe female choice

Answer 13

Female choice involves females assessing the fitness of males.

Question 14

When does genetic drift occur

Answer 14

Genetic drift occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next

Question 15

Why is genetic drift more important in small populations

Answer 15

Genetic drift is more important in small populations, as alleles are more likely to be lost from the gene pool

Question 16

When does population bottleneck occur

Answer 16

Population bottlenecks occur when a population size is reduced for at least one generation.

Question 17

Describe the founder effects

Answer 17

Founder effects occur through the isolation of a few members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool.

Question 18

Why is the gene pool altered by genetic drift

Answer 18

A gene pool is altered by genetic drift because certain alleles may be underrepresented or over-represented and allele frequencies change

Question 19

What happens when selection pressures are strong

Answer 19

Where selection pressures are strong, the rate of evolution can be rapid

Question 20

What are selection pressures

Answer 20

Selection pressures are the environmental factors that influence which individuals in a population pass on their alleles.

Question 21

Name the two types of selection pressures and give examples for each type

Answer 21

Biotic:

• competition
• predation
• disease
• parasitism

Abiotic:
Changes in
- temperature
- light
- humidity
- pH
- salinity

Question 22

What does the Hardy - Weinberg (HW) principle state

Answer 22

The Hardy-Weinberg (HW) principle states that, in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations

Question 23

What are the conditions for maintaining the HW equilibrium

Answer 23

The conditions for maintaining the HW equilibrium are: no natural selection, no random mating, no mutation, large population size and no gene flow (through migration, in or out).

Question 24

What is the HW principle used to determine

Answer 24

The HW principle can be used to determine whether a change in allele frequency is occurring in a population over time

Question 25

What is the HW principle used to calculate

Answer 25

Use the HW principle to calculate allele, genotype and phenotype frequencies in populations.

Question 26

What does it mean if there is a change in allele frequency

Answer 26

If there is a change in allele frequency it suggests evolution is occurring

Question 27

What is the formula for the calculation of the HW principle

Answer 27

p2 + 2pq + q2 = 1

Question 28

What does p, q, p2, 2pq and q2 stand for

Answer 28

p = frequency of dominant allele
q = frequency of recessive allele
p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q2 = frequency of homozygous recessive genotype

Question 29

What is fitness an indication of

Answer 29

Fitness is an indication of an individual’s ability to be successful at surviving and reproducing

Question 30

What is fitness a measure of

Answer 30

Fitness is a measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species.

Question 31

What does fitness refer to

Answer 31

It refers to the contribution made to the gene pool of the next generation by individual genotypes

Question 32

What can fitness be defined as

Answer 32

Fitness can be defined in absolute or relative terms

Question 33

Describe absolute fitness

Answer 33

Absolute fitness is the ratio between the frequency of individuals of a particular genotype after selection, to those before selection

Question 34

How to calculate absolute fitness

Answer 34

frequency of a particular genotype after selection

/ frequency of a particular genotype before selection

Question 35

What does the value of absolute fitness mean if

a) it is 1
b) it is greater than 1
c) it is less than 1

Answer 35

a) If the absolute fitness is 1, then the frequency of that genotype is stable.
b) A value greater than 1 conveys an increase in the genotype
c) and a value less than 1 conveys a decrease in the genotype

Question 36

Describe relative fitness

Answer 36

Relative fitness is the ratio of the number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype

Question 37

How to calculate relative fitness

Answer 37

number of surviving offspring per individual of a particular genotype
/ number of surviving offspring per individual of the most successful genotype

Question 38

What is Co-evolution

Answer 38

Co-evolution is the process by which two or more species evolve in response to selection pressures imposed by each other

Question 39

What does the change in the trait of one species act like on other species

Answer 39

A change in the traits of one species acts as a selection pressure on the other species

Question 40

Where is co evolution usually seen and what impacts do they usually have

Answer 40

Co-evolution is frequently seen in pairs of species that have symbiotic interactions
The impacts of these relationships can be positive (+), negative (-) or neutral (0) for the individuals involved

Question 41

Describe Mutualism

Answer 41

Mutualism: both organisms in the interaction
are interdependent on each other for
resources or other services. As both
organisms gain from the relationship, the
interaction is (+/+)

Question 42

Describe Commensalism

Answer 42

Commensalism: only one of the organisms benefits (+/0)

Question 43

Describe Parasitism

Answer 43

Parasitism: the parasite benefits in terms of energy or nutrients and the host is harmed as the result of the loss of these resources (+/-).

Question 44

What does the Red Queen hypothesis state and what does this mean

Answer 44

The Red Queen hypothesis states that, in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species
This means that species in these relationships must adapt to avoid extinction