Evolution - Lecture Four Flashcards
What is the definition of a species?
A population of reproducing organisms that is isolated form other populations
What is allopatric speciation?
When geographical separation causes different genetics, but not necessarily caused by different selection pressures
What are the different selection effects?
Directional selection
Disruptive selection
Stabilising selection
What is genetic drift?
When there is variation in the frequency of different genotypes
What is a founder effect/Bottleneck
When a sample of the original population is separated by chance and a small genetically similar population survive which lessens the gene pool
What is sympatric speciation?
When there are no physical barriers and a new species seems to develop spontaneously
What is an example of sympatric speciation?
The blackcap bird breeds in Europe but during the winter migrate to either the UK or Spain
Assortative mating occurs where the Spanish birds only breed with Spanish birds and UK only with UK
This causes rapid genetic change
What is allopolyploid speciation in plants?
Allopolyploidy is where organisms have two or more sets of chromosomes from different species
The allopolyploid offspring will be a hybrid, and creates a new species from the parent
What is a prezygotic barrier?
Barriers that effect the chance of hybridisation occurring, or the chance of two species breeding before the zygote is made
What are some examples of factors premating that act as prezygotic barriers
Habitat isolation, the two species never interact
Temporal isolation, their life cycles never align
Behavioural isolation, they have different mating rituals meaning one species doesn’t want to mate with the other
What are some factors post mating that act as prezygotic barriers?
Mechanical isolation, where they can’t mate due to anatomical differences
Gametic isolation, some animals can’t fertilise each other because their gametes don’t recognise each other
What are postzygotic barriers?
Barriers that prevent hybridisation after the zygote has been made
What are some examples of postzygotic barriers?
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
What is meant by hybrid zones?
Hybrid zones are different outcomes when two groups of hybrids meet and gene flow may be present
What are the three different hybrid zones that occur when two groups meet?
- Fusion between the two groups, occurs when there is lots of gene flow
-Reinforcement of isolation, occurs when there is some gene flow leading to a loss of fitness
-Stability, occurs when there’s already such a limited gene flow that fitness loss is negligible
