Define Species (2)
- population of reproducing organisms isolated from other populations
- Group of individuals with common ancestor, capable of interbreeding and producing a FERTILE offspring
if the there is NO gene flow, does that indicate species are different?
· If there is no GENE flow it doesn’t necessarily mean the species are different, for example there is 5 subspecies of Giraffes but and they’re aesthetically different in patterns, this doesn’t indicate a different species, because they do not live near each other so of course there will be no gene flow.
In which way can speciation occur?
- In time along lineage= humans/chimpanzee
- geographical isolation
- genetic factors like genetic bottleneck/genetic drift
Different species can be identified using GENE comparison, die there have to be a SPECIFIC amount of gene differences to indicate speciation?
Different species can be identifies by comparing GENES of the population, there is not a specific amount of different genes that divides two species, it could be 1 gene as it could be 1000s as long as they can reproduce.
What is allopatric speciation?
-Species are geographically isolated
- leads to REPRODUCTIVE ISOLATION (no gene flow)
- resulting in 2 different species
-
What id directional selection
- ONE extreme is favours
What is stabilising selection?
- Middle/ mean is favoured
- e.g cat with long tail cannot balance
cat with short tail cannot balance properly either, MEDIUM sized tail is favoured
What is disruptive selection
both EXTREME are favoured
EX. Short tails help keep predators
from catching you on the ground.
Long tails are good for balance in
the trees. Medium tails don’t help.
What other ways beside natural selection can speciation occur?
GENETIC DRIFT
WHAT is GENETIC BOTTLENECK
Genetic Bottleneck:
-When an event causes big reduction
in a population’s size & gene pool.
Certain alleles may be due to
the event & population will also be
subject to genetic drift.
what is FOUNDER EFFECT?
When a new pop. Is established by small number of
Individuals -> founding population will have low genetic diversity -> heavily influenced by genetic drift.
What is sympatric speciation?
Speciation that occurs within a a population that id NOT due to geographical isolation
What is Parapatric speciation?
Speciation that occurs between species that are not completely geographically isolated, they’re somewhat isolated.
How does sympatric speciation supposedly occur?
- Most common scenario involves DISPRUPRTIVE SELECTION
- 2 Species diverege, where extreme are favoured
- so if hybridisation occurs within these species, the hybrid is in-between and wont survive and reproduce to pass on genes
- speciation can then occur if the species EXCLUSIVELY mate with the same extreme individuals
Why is SYMPATRIC SPECIATION so hard to achieve?
because of the GENETIC RECOMBINATION between species
What 4 conditions are required for SYMPATRIC speciation?
- Species must be largely sympatric ( while species have separated sympatrically but then were affected by allopatric it is hard to prove it was due to sympatric)
- Species must show REPRODUCTIVE isolation
- sympatric taxa must be close relatives
- Biogeographic must make ALLOPATRIC speciation very unlikely
Can you give example of species tin which sympatric speciation occurred?
- Cichlid Fish
- Palm trees on lord howe island
- Polyploidy in plants
What is poliploydi in plants?
polyploidy in plants is
a type of sympatric speciation
in which two sympatric species
having different chromosome
numbers or morphologies form a
hybrid, and that hybrid produces
offspring with a doubled number
of chromosomes (one full genome
from each parental species).
This yields a new lineage that
is reproductively isolated from
both ancestral species. Polyploid
speciation is quite common in
plants, perhaps accounting for up
to 4% of new angiosperm species.
What is ASSORTATIVE mating?
Sexual selection in which individuals with similar phenotypes/genotypes interbreed more frequently than expected under a random mating pattern
e.g. Blackcap Birds -> breed in Germany -> some overwinter fly in Spain, others fly in UK
This leads to Assortative mating – Spanish birds mating with Spanish birds, UK with UK -> due to arrival time on breeding grounds (UK closer to Germany) -> Reproductive Isolation between 2 groups so over time= Genetic Change
What is PREYGOTIC barrier?
eggs of an organism fail to be fertilized
What is POSTZYGOTIC barrier?
- mechanism that blocks reproduction after fertilization and zygote formation
- POSTZYGOTIC barriers which occur after fertilization. In this case, the offspring are produced but they are sterile or not viable
What is HYBRID zone?
area where two different population meet and breed
Describe and explain the outcome the 3 of hybrid zones?
Reinforcement: Hybrids/ Offspring which are a less fit to survive, the hybrids are less likely to survive and pass on genes: so therefore species diverge until hybridization can no longer occur.
