Biological evolution Flashcards
Definition of genetic drift
(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
Definition of gene flow
movement of genes / alleles from one population to another (via migration)
Ecological concept of species
- 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
- diff species: the difference in traits has led to a change in their role in the ecosystem,
Genetic concept of species
- (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
Phylogenetic concept of species
- 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
Morphological concept of species
- 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
- same species: members have different …(trait)… but they look largely similar to each other based on physical characteristics
Biological concept of species
- 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
Mechanism of speciation
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
What is allopatric speciation
- barrier at step 2 is a
PHYSICAL barrier which keeps
one population geographically separated isolated from the rest of the species
What is sympatric speciation
- 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)
Autopolyploidy
- 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
Allopolyploidy
- 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
How natural selection can lead to speciation
- 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
How ecological opportunities can trigger adaptive radiation
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
How evolutionary novelties trigger adaptive radiation
- 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
