Stage 1 Biology Speciation L Notes
Topic One: Speciation
Speciation: The process of one species becoming two
Species:
- Have similar morphology
- Have very similar DNA and amino acid sequences in particular proteins
- Can mate to produce fertile offspring
Biochemistry
- More closely related organisms or organisms of the same species share similar DNA and amino acid
sequences since they have all evolved together
Morphology
- DNA codes for proteins. Proteins allow for structure and function
- Therefore, organisms of the same species have similar morphology
Steps for Allopatric Speciation
Mnemonic Device: A for Apart
1. Two parts of a population are separated by a geographical barrier. e.g. river, lake, mountain range, desert
2. Interbreeding between these two groups stops
3. The gene pools separate and there is no gene flow between them.
4. The selective pressures on each side of the geographical barrier will be different if the two environments
differ for each group.
- The two populations become different if the selective agents differ and will not be capable of inter-breeding.
- The species are now separate species and are reproductively isolated. They will be named accordingly.
Topic Two: Reproductive Isolation
- Caused by reproductive barriers which prevents breeding to produce fertile offspring between species
- The barriers can either be pre-zygotic or post-zygotic
Pre-zygotic
- Temporal: Some closely related plant species release pollen at different times of the year
- Mechanical: Genitals physically won’t fit together
- Behavioural: Some closely related birds perform dances which only attract females from their own species
- Gamete: Mating can occur but sperms and egg can’t fuse
Post-zygotic
- Hybrid sterility
- Hybrid invariability (Zygotes can form but are weak and develop poorly)
Divergent Evolution
- The accumulation of small differences between close populations leading to speciation.
- Evidence can be seen in homologous structures
Convergent Evolution:
- The development of similar traits on organisms that are not closely related due to similar selective pressures
in similar areas
- Examples: wings in insects, birds, bats, dinosaurs
- Same function, different ancestors
Topic One: Speciation
Speciation: The process of one species becoming two
Species:
- Have similar morphology
- Have very similar DNA and amino acid sequences in particular proteins
- Can mate to produce fertile offspring
Biochemistry
- More closely related organisms or organisms of the same species share similar DNA and amino acid
sequences since they have all evolved together
Morphology
- DNA codes for proteins. Proteins allow for structure and function
- Therefore, organisms of the same species have similar morphology
Steps for Allopatric Speciation
Mnemonic Device: A for Apart
1. Two parts of a population are separated by a geographical barrier. e.g. river, lake, mountain range, desert
2. Interbreeding between these two groups stops
3. The gene pools separate and there is no gene flow between them.
4. The selective pressures on each side of the geographical barrier will be different if the two environments
differ for each group.
- The two populations become different if the selective agents differ and will not be capable of inter-breeding.
- The species are now separate species and are reproductively isolated. They will be named accordingly.
Topic Two: Reproductive Isolation
- Caused by reproductive barriers which prevents breeding to produce fertile offspring between species
- The barriers can either be pre-zygotic or post-zygotic
Pre-zygotic
- Temporal: Some closely related plant species release pollen at different times of the year
- Mechanical: Genitals physically won’t fit together
- Behavioural: Some closely related birds perform dances which only attract females from their own species
- Gamete: Mating can occur but sperms and egg can’t fuse
Post-zygotic
- Hybrid sterility
- Hybrid invariability (Zygotes can form but are weak and develop poorly)
Divergent Evolution
- The accumulation of small differences between close populations leading to speciation.
- Evidence can be seen in homologous structures
Convergent Evolution:
- The development of similar traits on organisms that are not closely related due to similar selective pressures
in similar areas
- Examples: wings in insects, birds, bats, dinosaurs
- Same function, different ancestors
