Biological evolution

Question 1

Definition of genetic drift

Answer 1

(1) Random change of allele and genotype frequencies,
(2) as a result of chance alone,
and can differ from generation to generation
(3) in a small gene pool / population

Question 2

Definition of gene flow

Answer 2

movement of genes / alleles from one population to another (via migration)

Question 3

Ecological concept of species

Answer 3

• a group of organisms in
  
  • (1) similar ecological niches
  • (2) with unique adaptations due to its particular role in a biological community
• how to use concept to argue for same or different species
  
  • diff species: the difference in traits has led to a change in their role in the ecosystem,
    e.g. different ability to camouflage in diff envts, different predators which prey on them
  • limitation: changes in behaviours/predators may result in different definition of species

Question 4

Genetic concept of species

Answer 4

• (1) genetically distinct organisms
  (2) that share common gene pool
• how to use concept to argue for same or different species
  
  • same species: members are genetically similar
  • diff species: multiple alleles at each gene locus result in different nucleotide sequences in members with different …(trait)…
    ->sufficient genetic differences
  • limitation: genetic distance should be measured using the entire genome, but only a small part of genome is used

Question 5

Phylogenetic concept of species

Answer 5

• Smallest groups of organisms that
  share a common ancestor
• how to use concept to argue for same or different species
  
  • same species: members share a high degree of similarity in ** homologous structures**, and thus form the smallest grp that share a common ancestor
  • diff species: members do not share sufficiently high degree of homology, and thus has a more distant common ancestor
  • limitation:
    
    • genetic distance should be measured using the entire genome, but only a small part of genome is used
    • differences between organism species at genetic level may not show up in phenotype

Question 6

Morphological concept of species

Answer 6

• a group of organisms with
  similar anatomical traits
• how to use concept to argue for same or different species
  
  • same species: members have different …(trait)… but they look largely similar to each other based on physical characteristics
    + give example of a defining feature
  • diff species: members look very different from each other due to the difference in traits
  • limitation: differences between species at genetic level may not show up in phenotype

Question 7

Biological concept of species

Answer 7

• a population or group of population whose members have the
  
  • (1) potential to interbreed
  • (2) and produce viable fertile offspring (VFO)
• how to use concept to argue for same or diff species
  
  • same species: genes only affect …(other characteristic, e.g. coat colour)… and not traits which affect their ability to interbreed with each other
  • diff species: preferential/selective breeding of specific members with specific trait
    -> thus do not interbreed
  • limitation: difficult to know if geographically isolated pops can potentially interbreed

Question 8

Mechanism of speciation

Answer 8

Step 1: Single population
- can interbreed to produce VFO
- reproductively and genetically isolated from other species

Step 2: Barrier develops
- still considered a species as members can still interbreed if brought together

Step 3: Differentiation
- absence of gene flow
-> behavioural isolation + reproductive isolation
- NS due to different environments with different selection pressures

Step 4: Barrier disappears
- by then, accumulation of sufficient RIMs, adaptations and genetic diversity -> reproductive isolation where cannot produce VFO

Question 9

What is allopatric speciation

Answer 9

• barrier at step 2 is a
  PHYSICAL barrier which keeps
  one population geographically separated isolated from the rest of the species

Question 10

What is sympatric speciation

Answer 10

• RIMs (Step 4) develop at the start of the speciation process
• new species evolve within the SAME geographic region as parental species or geographically overlapping population(s)

Question 11

Autopolyploidy

Answer 11

• Involves chromosomes from the same species
• Process:
  (1) Non-disjunction leads to formation of plant with double chromosomes, which will have gametes through meiosis
  (2) Plants cannot form VFO if mating with parent plant
  due to odd no of chromosomes
  -> cannot form homologous pairs
  -> cannot separate
  normally during meiosis

=> Speciation has occured

Question 12

Allopolyploidy

Answer 12

• involves chromosomes from 2 or more species
• process:
  (1) hybridisation where haploid gametes from 2 different species combine
  (2) sterile hybrid formed
  due to chromosomes not being homologous
  -> cannot pair up during meiosis

=> Speciation has occurred

Question 13

How natural selection can lead to speciation

Answer 13

• Disruptive selection
• where gene pool of one pop may become split into 2 gene pools over time
• leads to step 3 (differentiation) and step 4 (barrier disappears) of speciation

Question 14

How ecological opportunities can trigger adaptive radiation

Answer 14

1a. where either there is availability of new resources through ecological opportunities
(i.e. previously occupied ecological niches now being free)
1b. or adaptive zones where ecological opportunities are available and were not exploited by an ancestral organism
2. thus, an original colonising group
(a) encountered no competitors,
(b) and diversified in a way that led to the efficient use of the available resources by a group of descendant species
3. organisms eventually developed adaptations that can make them better adapted to the habitat they occupy
4. and in the process, succeeding generations diversify into new species, leading to rapid speciation from ancestral species

Question 15

How evolutionary novelties trigger adaptive radiation

Answer 15

• evolution of a key morphological trait - one that allowed descendants to live in new areas, exploit new sources of food, or move in new ways
• modifications of pre-existing structures
• thus supporting rapid speciation and ecological divergence

Question 16

How major changes in climate could trigger mass extinctions

Answer 16

• adversely affect plants and animals which lacked the genetic flexibility to adapt
• example:
  
  • marine organisms are adapted to steady unchanging envt
  • if earth’s temp change by a few º overall, many marine species would perish

Question 17

How catastrophes could lead to mass extinction

Answer 17

• lead to changes in envt
• example: extinction of dinosaurs
  where extra-terrestrial object collided with earth
  -> dust ejected into atmosphere on impact block much of the sunlight
  -> kill many plants and therefore terrestrial animals (i.e. disrupted food chain)

Question 18

Definition of microevolution

Answer 18

concerned with patterns of change within a population or species

Question 19

abiotic factors

Answer 19

• light intensity or wavelength
• temperature
• humidity
• wind or air movement
• soil quality

Question 20

how to explain that a certain characteristic shows continuous variation

Answer 20

• the variation shows non-discrete phenotypes
• characteristic is determined by several different genes
• which each have a small and additive effect
• some of the genes even have multiple alleles
• hence giving rise to multiple combinations of genotypes, hence increasing the possible variations in phenotypes
• variation in phenotypes are also influenced by environmental conditions