Populations in Ecosystems 2.0 Flashcards
What is the purpose of the Hardy Weinberg Principle?
Mathematical equation used to predict the frequencies of alleles in a population
What is the equation for the Hardy Weinberg Principle?
p^2 + 2pq +q^2 = 1
p^2= no. of individuals that are homozygous dominant (AA) 2pq= no. of individuals that are heterozygous (Aa or aA) q^2= no. of individuals that are homozygous recessive (aa) 1= all alleles present
What steps do you follow for Hard Weinberg Principle?
Calculate q^2 = fraction q = square root p + q = 1 1 - q = p 2pq Percentage
What assumptions should we make when using the Hardy Weinberg Principle?
No selection No mutations No migration Large population Random mating
What MUST we assume when using the Hardy Weinberg Principle?
The proportion of dominant and recessive alleles of ANY gene in a population remains constant from one generation to the next
What is selection?
The process by which organisms better adapted to their environment tend to survive and breed at the expense of those less well adapted
What is phenotypic variation a result of?
Genetic factors
Environmental factors
Why does genetic variation occur?
Meiosis
Sexual reproduction
Mutations
Describe directional selection
Graph moves right/left
Change in environment
Change in mean
Extreme selected
An example of directional selection?
Moths
Describe stabilising selection
Graph squishes inwards
Both extremes
Phenotypic variation decreases
Environment remains stable
An example of stabilising selection?
Birth weight
Why does natural selection occur?
Random mutation in gene pool
Become advantageous trait in specific environment
Mutation = better adapted
Organisms survive at the expense of those less adapted
Reproduce
Allele frequency increases in gene pool
Evolution
Name some selection pressures
Predation
Natural disaster
Competition
Disease
What are selection pressures?
Environmental factors that limit population of a species
What do selection pressures determine?
The frequency of all alleles within the gene pool
Evolution only occurs by natural selection if…
Organisms reproduce
Have sufficient resources
Genetic variation
Phenotypic variation
In order for populations to survive + increase exponentially they must…
Have a suitable population size
Minimise intraspecific competition
Have high reproductive success
What factors make populations survive + increase exponentially unlikely?
High death rates from predation
Low parental investment
Lack of resources
Why is death rate not random?
Organisms better adapted survive
What is variation essential for?
Chagrining environment
New disease
New predators
New competition
Describe disruptive selection
Least common form
Opposite to stabilising
Favours extremes at the expense of intermediate phenotypes
Examples of disruptive selection
Mean fur lengths
Coho salmon
What is speciation?
The evolution of new species from existing species, that enables evolutionary change and diversity
What is speciation due to?
Reproductive isolation
Genetic differences (mutations)
Geographical isolation
What are the two forms of speciation?
Allopatric
Sympatric
Describe allopatric speciation
Most common
Different location
Geographic separation
Describe sympatric
Less common
Same location
Reproductive isolation
How does allopatric speciation occur?
Barrier occurs preventing migration between population Environment of each new range may be different Different mutations occur in each range Different selection pressures Selection favours advantageous allele No gene mixing of alleles Changes in allele frequency Unable to interbreed EVEN if barrier removed
What is adaptive radiation?
The diversification of species into forms adapted to different ecological niches
How do sympatric speciation occur?
eg. Apple maggot fly…
Only lay eggs inside Hawthorns Fruits
Apple trees introduced
Some flies lay eggs in apples
Mates are found by searching site they were raised
Raised in apples = mates wit flies raised in apples
Mutations may result in two new species
What is genetic drift?
Genetic change due to CHANCE
What will there be in smaller populations?
Smaller variety of alleles
Not equal chance of each allele being passed on
OR if a mutation passed on quickly
Speciation more likely
