Natural Selection/Speciation (5.2, 10.3)

Question 1

Natural Selection

Answer 1

The process by which random, evolutionary changes are selected for by nature in a consistent, orderly, non-random way. In simpler terms, the increase or decrease in the frequency of certain alleles within a population.

Question 2

What did Darwin mean by ‘survival of the fittest’?

Answer 2

It is not necessarily the strongest or most intelligent species that survive, but the ones that are most responsive to change.

Question 3

What are the key components of the process of Natural Selection? (Hint: Mnemonic).

Answer 3

• Inherited variation exists within the population - Competition results from an overproduction of offspring- Environmental pressures lead to differential reproduction- Adaptations which benefit survival are selected- Genotype frequency changes across generations hence- Evolution occurs within the population

Question 4

Define population

Answer 4

A group of organisms of the same species living in the same area at the same time.

Question 5

Define gene pool

Answer 5

The sum total of all genes/alleles that are present in a population.

Question 6

What are the contributors to genetic variation in a population?

Answer 6

Mutations - These add new alleles to a populationMeiosis (through independent assortment and crossing over) - Creates new gene combinationsSexual Reproduction - Different zygotes are formed by random fertilisation

Question 7

What is the Malthusian dilemma?

Answer 7

Populations multiply geometrically (i.e. exponentially) while food sources increase arithmetically (i.e linear).

Question 8

What types of adaptations are there?

Answer 8

Structural - Physical differences in structureBehavioural - Differences in patterns of activityPhysiological - Differences in detection and response by vital organsBiochemical - Differences in enzyme and cell functionsDevelopmental - Variable changes across a life span (eg. ageing patterns, meiosis).

Question 9

Why are allele frequencies in a gene pool of a population constantly changing?

Answer 9

Because if the environment changes, what constitutes a beneficial/detrimental trait is subject to change.

Question 10

Describe how the Peppered moths show Natural Selection

Answer 10

There is a naturally occurring mutation for dark-coloured moth wings. However, the mottled wing moths had a higher survival rate and made up most of the Peppered moth’s population as it was able to camouflage against the lichen on trees and hide from predators. During the Industrial Revolution in the 19th century, the pollution from fossil fuels killed the lichen on the trees so the dark-coloured wing allele became the more beneficial trait for survival. Hence, the frequency of this allele increased. Then, in the 20th century once fossil fuel use decreased the mottled wing allele became more common once again as lichen regrew on the trees.

Question 11

Describe the Galapagos finches

Answer 11

Different species of finch evolved on different islands. As each island had a different environmental habitat and food sources the finches underwent adaptive radiation. This is seen through the shapes of their beaks, which are adapted for different purposes.

Question 12

Describe antibiotic resistance in bacteria

Answer 12

In a bacteria colony, over several generations, a proportion of the bacteria can develop a resistance to the antibiotic through genetic mutation. Then, the following generations become immune to this antibiotic and it is ineffective against the bacteria.

Question 13

Define allele frequency

Answer 13

The proportion of a particular allele within a population.

Question 14

What is the formula to find the allele frequency?

Answer 14

Allele frequency = specific allele/total number of alleles

Question 15

Define gene flow

Answer 15

The movement of genes into/out of gene pools.

Question 16

What are the mechanisms for changing allele frequencies in a gene pool?

Answer 16

Mutations - new allelesGene flow - immigration and emigrationNatural selection - undesirable traits decrease in frequencyNon-random mating - assortative mating

Question 17

Give examples of prezygotic mechanismsHINT: GEBTSG

Answer 17

Geographical isolation- Physical barriers prevent mating eg. land, waterEcological isolation- Different habitatsBehavioural isolation- Different specific courtship patternsTemporal isolation- Different maturity times/reproductive cyclesStructural incompatibility- Physical differences prevent copulation/pollinationGamete mortality- If the egg and sperm fail to unite

Question 18

Give a examples of postzygotic mechanisms

Answer 18

Hybrid inviability- Hybrids are produced but fail to reach reproductive maturityHybrid infertility- Hybrids fail to produce functional gametes i.e. viable but NOT sterile

Question 19

Define speciation

Answer 19

The process by which new species are formed by the splitting of an existing species. Occurs when the gene flow between populations ceases.

Question 20

What are the two types of speciation?

Answer 20

Allopatric and sympatric speciation.

Question 21

What is allopatric speciation?

Answer 21

The formation of new species in different geographical areas. It occurs when a geographical barrier physically isolates populations.

Question 22

Steps of allopatric speciation

Answer 22

1) Migration2) Geographical isolationGradual formation of physical barriers that isolates parts of the population.3) Formation of a subspeciesThe isolated population may be subjected to different selection pressures so their allele frequencies change and the population becomes a subspecies.4) Reproductive isolationThe separated subspecies undergoes changes to their genetic makeup. This prevents mating with individuals from other populations.

Question 23

What is sympatric speciation?

Answer 23

The divergence of a species within the same geographical location.

Question 24

What is the most common cause of sympatric speciation?

Answer 24

Polyploidy (a mutation that involves the multiplication of whole sets of chromosomes). This instantly reproductively isolates those individuals from their parent population.

Question 25

Define phyletic gradualism

Answer 25

Speciation is a smooth and continuous process. The environment changes slowly and big changes result from many small cumulative changes. Intermediary forms connect the ancestral species to the modern species.

Question 26

Define punctuated equilibrium

Answer 26

Speciation is a periodic process. The environment changes rapidly. Big changes occur suddenly, followed by long periods of no change. There are no intermediary forms.

Question 27

Define stabilising selection

Answer 27

When the average phenotype is favoured at the expense of the two extremes. Maintains the population in a stable form.

Question 28

Define directional selection

Answer 28

Favours the phenotype of one extreme so there is a shift in the average in one direction.

Question 29

Define disruptive selection

Answer 29

Favours the extreme phenotypes at the expense of the average. Continued separation can cause speciation.

Question 30

Define genetic drift

Answer 30

Random changes in the allele frequencies of a population.

Question 31

Define The Founder Effect

Answer 31

A small group breaks away from a larger population to colonise a new territory. (The island was already there! No forming of geographical barriers so not a reproductively isolating mechanism).

Question 32

Define Population Bottleneck

Answer 32

A significant reduction in population size due to an event (eg. climate change, human influence).