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
Gametic isolation
Incompatibility between gametes prevent hybrid from forming
Hybrid isolation
Organisms interbreed but offspring are infertile eg horse and donkey can reproduce to produce a mule but mule is infertile
Describe what is meant by allopathic speciation. 6marks
Geographical isolation
Separate gene pool
Variation due to mutation
Different selection pressures
Selection for advantageous alleles
Those organisms survive to reproductive
Leads to change In allelic frequencies
Can not mate to produce fertile offspring
Describe what is meant by sympatric speciation 6marks
Not geographical isolation
Leads to reproductive isolation
Separate gene pools
Selection favours advantageous allele
Organisms that survive reproduce
Leads to change in allelic frequency
Can not reproduce to produce fertile offspring
Describe the process of succession
Pioneer species invade
Change environment factor
Pioneer species makes environment less hostile for new species
New species cause changes that are less suitable for previous species
Change in biodiversity
Stability increases
Climax community
Describe random sampling (5points)
Use grid
Random coordinates
Count number of plants in quadrant
Large sample
Valid method of calculating total number of plant eg mean number of plant per quadrant
Describe systematic sampling
Transect
Place quadrants at regular intervals along line
Calculate percentage cover
Describe how to calculate percentage cover
Random number finer
Large number of quadrats
Total percent dived by number of quadrat
Describe mark release recapture
Capture sample mark and release
Method that does not harm organisms
Take second sample and count marked individuals
Number in sample 1 x number of sample 2 divided by marked in sample 2
Describe how you would determine how many quadrats to use when investigating a habitat 5marks
Calculate running mean
When enough quadrats this shows little change
Enough to carry out statistical test
Large number so results are reliable
Need to ensure work can be done in time available
