Populations And Evolution Flashcards
Species
An organism that can reproduce to produce fertile offspring
Population
All the organisms of one species in one place at one time
Community
All the organisms of all the species in one place at one time
Gene pool
All the alleles present in a population
Allele frequency
How common an allele is in a population
Evolution
A change in allele frequency over time and over many generations
Differential reproductive success
Organisms with a phenotype better adapted to their environment have a selective advantage and are more likely to survive and reproduce
Speciation
The process of forming a new species
The hardy weinberg principal
A model predicting the frequency of alleles in a population, that will stay constant over generations providing there is no mutation no selection and it is a large population
What are the two equations for hardy Weinberg
p+q=1
p is usually dominant, q is usually ressesive
p2+2pq+q2=1
Intraspecific variation
Individuals of the same species have the same genes but different alleles- variation in their phenotype
Interspecific variation
Individuals of different species have different genes and live in different environments- variation in their phenotype
Continuos variation
Variation is smooth and continuous (not discrete), represented on a line graph e.g weight and height
Discontinuous variation
Individuals fall into discrete groups with no intermediates, represented in a bar chart e.g bloody type, controlled by a single gene with a few alleles
Mutation, meiosis crossing over/independent seg., random fertilisation
Genetic causes to variation
Environmental causes to variation
Environment changes the phenotype, can change over a lifetime e.g accent
Both environmental and genetic causes to variation
E.g height, genetic because you have tall parents, environmental because of you childhood nutrition
Allopatric speciation
Geographical isolation so reproductive isolation (no gene flow)
Sympatric speciation
Not geographically isolated but are reproductively isolated, e.g seasonal reproductivity, behavioural courtship, hybrid sterility
Name the steps that occur due to both allopatric and sympatric spectiation
- Variation exists in pop. due to mutation
- Different selection pressures
- Directional selection of different phenotypes
- Different reproductive success
- Change in allele frequency over many generations
Genetic drift
Change in allele frequency between generations due to random chance e.g random fertilisation
What does genetic drift affect
Small populations much more than large ones, changes the allele frequency, does not depend on the environment
Directional selection
Individuals with more extreme characteristics are more likely to survive and reproduce e.g antibiotic resistance, change in environment, mean phenotype changes
Stabilising selection
Individuals with extreme characteristics are less likely to survive and reproduce e.g human birth weight, stable environment, mean phenotype remains the same
Disruptive selection
Both extremes of the phenotype are more likely to survive and reproduce than the mean phenotype, opposite to STABILISING selection, contributes to sympatric speciation
Give an example of disruptive selection
The environment is made of black and white rocks and but the genotype is white black and grey, both extremes (white+black) can hide from predators as they blend in
Abundance
The number of individuals of a single species in an ecosystem (population)
Distribution
Where a species is found in an ecosystem
Intraspecific competition
Competition within a species where they occupy the same niche and compete for everything e.g food and mates
Carrying capacity
The maximum stable population an ecosystem can support
Limiting factor
The factor that limits max population size
Interspecific competition
Competition between species, the abundance of one species affects the other, species with a similar niche will compete for resources
Predator prey relationship
Increase of prey, increase of predator due to more food, decrease of prey, decrease of predator. Time lag and on a cycle
Abiotic factors
Species can tolerate a range of conditions, where conditions are optimal pop size will be biggest, altitude, temp, pH
Niche
The role an organism plays in an ecosystem
Each species has its own niche
Two species can’t occupy the exact same niche because they both compete fore everything, the abundance will vary depending on the competition, the distribution will vary because an organism can only exist where it’s niche exists
