Selection And Speciation Flashcards
A new mutation could:
Create a selection advantage
Be neutral
Create a selection disadvantage
How does the environment influence phenotype
It influences the way genes are expressed, genotype sets limits for characteristics the environment determines where within the limits the organism lies
What are examples of environmental factors
Climatic condition eg temperature
Abiotic and biotic factors
Continuous variation
Characteristic controlled by more than one gene and environmental factors okay a major role in where on the continuum an organism loes
Stabilising selection
Selection at both ends
Favours the average
Reduces genetic variation
Tends to eliminate extremes
Reduces opportunity for evolutionary change
Occurs where the environment is stable
Directional selection
Mean of the population represents the optimum phenotype of the population.
Change in environmental conditions produce new selection pressures which favour an extreme phenotype
over time the allele combination will dominate and there will be a mean shift
Disruptive selection
Environment has selection pressures that favour two extreme phenotypes overtime these two extremes will dominate and the mean will shift in both directions
Least common type of selection but most important
Eg in a beach white mice can hide in patches of sand and long grass and black mice can hide in thick grass whereas medium mice can’t hide anywhere
Reproductive isolation
Period where two distinct populations are prevented from breeding
So they become genetically distinct through an accumulation of mutations and different selection pressures
Genetic bottleneck
Sudden decrease in population
Reducing genetic variation
Allopathic speciation or geographical isolation
Any physical barrier which separates a population preventing interbreeding eg a river or a mountain
Each population subjected to different selection pressures and adapt over generations due to natural selection
Mutations occur in each population changing genotype and maybe phenotype so when populations reunite they are too different for interbreeding and are reproductively isolated
Each population became their own species with its own gene pool
Sympatric speciation
Two populations become reproductively separate due to other reasons than geography such as choice of food or choice of season to mate
What are the types of isolation
Temporal
Ecological
Behavioural
Mechanical
Gametic
Hybrid
Temporal isolation
Organisms breed at different times in the year
Ecological isolationw
Different habitats within the same area
Behavioural isolation
Different behavioural patterns eg courtship behaviour
