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12032254
Populations and Evolution
Beschreibung
A Level Biology Populations and Evolution A2
Keine Merkmale angegeben
biology
section 7
a2
Mindmap von
Dominic Weston
, aktualisiert more than 1 year ago
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Erstellt von
Dominic Weston
vor mehr als 6 Jahre
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Zusammenfassung der Ressource
Populations and Evolution
Definitions
Population
Group of individuals belonging to the same species living in a particular area
Species
Group of similar organisms that can reporduce to give fertile off spring
Gene Pool
Complete range of alleles present in a population
Allele Frequency
How often an allele occurs in a population
Hardy-Weinberg Principle
Predicts that allele frequencies wont change from one generation to the next
Only true if
Large population
That is isolated
With No Mutations
And No Natural Selection
And there is Random Mating
Hardy-Weinberg equations used to test whether or not ...
Predicting Allele frequency
p + q = 1
p - Frequency of Dominant allele
q - Frequency of Recessive Alleles
1 is the entire population
Predicting Genotype Frequency
p^2 + 2pq + q^2 = 1
p^2 is frequency of homozygous dominant
2pq is the frequency of heterozygous
q^2 is the frequency of Homozygous Recessive
Speciation
Evolution of a species from an existing one
Isolation Mechanisms
Geographical
Isolated by geographical barrier
Ecological
Pop dont meet as inhabit different areas
Temporal
Breeding seasons dont coincide
Behavioural
Any mutation that prevents courtship
Mechanical
Physical differences that prevent mating
Gametic
Prevents gametes from meeting
Hybrid sterility
Offspring of different species that are sterile
Genetic Drift
Can lead to Speciation
Greater effect in small populations
Where chance dictates
who survives and breed to pass on alleles
Rather than environmental factors
Two forms of speciation
Allopatric
When a geographical barrier seperates
Two populations of the same species
If environmental conditions are different between the two populations
Natural selection will occur to favour optimal alleles
(Oceans, rivers, mountains, deserts)
Sympatric
No geographical barrier
Reproductive isolation still occurs
Different timings of breeding seasons
Different location preferences for mating or feeding
Random mutation can prevent breeding between population
Natural Selection
Process
A new mutation arises in the population
Slightly better adapted to the environment
Due to overpopulation, only individuals who are better adapted will survive
Individuals who survive are more likely to reproduce and pass on the alleles to the offspring
Better adapted alleles become more common in the population over time
Link to context
Variation in Phenotype
Variation due to Genetics
Mutations
Meiosis
Crossover of chromosomes
Independent assortment
Random Fertalisation of gametes
Results in distinct characteristics
Discrete data
Variation due to Environment
Amount of light
Infectious diseases
Access to nutrients
Continuous variations in characteristic
Forms a normal-distruibution curve
Effects of different forms of selection on evolution
Stabilising Selection
Perserving the average phenotype of the population
Selection against extremes in the population
Usually when environmental conditions are stable
Directional Selection
Changes the phenotype to favour phenotype in one direction from the mean population
E.g. Antibiotic Resistant Bacteria
Disruptive Selection
Favours extreme phenotypes
At expense of mean phenotype
Mean can split into two extremes
Due to environmental factors take two distinct forms
Causes two distinct seperate species
Medienanhänge
Graphs To Show Natural Selection (binary/octet-stream)
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