L1 - Gene Pools (& selection) Flashcards
Define Population
A group of organisms of the same species living in a particular area at a particular time - they have the potential to interbreed
Define Allele frequency
How often an allele occurs in a population
Define Gene pool
The complete range of alleles present in a population
Why can some genotypes not be measured by looking at the phenotypes?
If a trait is recessive e.g. blue eyes, if the organism has this trait then they would be homozygous recessive. However, if they did not, you don’t know if they’re heterozygous, or homozygous dominant
State the 7 conditions required for Hardy-Weinburg equilibrium
1) No mutations
2) No natural selection
3) Very large population
4) All members of the population breed
5) Random mating
6) All parents produce the same number of offspring
7) No migration in or out
State the Hardy-Weinburg equilibrium equation for genotypes
p^2 + 2pq + q^2 = 1
p^2 = Frequency of homozygous dominant genotypes
2pq = Frequency of heterozygous genotypes
q^2 = Frequency of homozygous recessive genotypes
State the Hardy-Weinburg equilibrium equation for alleles
p + q = 1
p = Frequency of the dominant allele
q = Frequency of the recessive allele
Define variation
The difference in characteristics shown by organisms belonging to the same natural population or species
State the two types of variation
Continous and discontinuous
In discontinuous variation, the phenotypes…
4 points
1) Have distinct categories
2) Normally qualitative, with no overlap between categories
3) Are controlled by a small number of alleles
4) Are affected by the environment very little
(The opposite to continuous variation!)
Give 3 examples of discontinuous variation
a) ABO blood groups
b) Tounge rolling
c) MN blood groups
In continuous variation, the phenotypes…
4 points
1) Have no distinct categories
2) Normally quantitative, with overlaps between categories
3) Controlled by a large number of alleles (polygenic inheritance)
4) Are influenced largely by the environment
(The opposite to discontinuous variation!)
Which HAS gaps between categories, bar chart or histogram?
Bar chart
Which has NO gaps between categories, bar chart or histogram?
Histogram
Define stabilising selection, draw the graph and give an example
Stabilising selection = Where individuals with alleles for characteristics towards the mean are more likely to survive and reproduce. It occurs when the environment isn’t changing and it reduces the range of possible phenotypes
Example = Human birth weights
Define directional selection, draw the graph and give an example
Directional selection = Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. This could be in response to an environmental change
Example = Antibiotic resistance in bacteria
Define disruptive selection, draw the graph and give an example
Disruptive selection = Where individuals with alleles for both extreme phenotypes (at either end of the range) are more likely to survive and reproduce. Occurs when the environment favours more than one phenotype
The opposite to stabilising selection, as characteristics towards to middle of the range are lost.
Example = Beak size in birds
Define Selection pressure
Any factor that affects an organism’s chance of survival and reproduction
Define Evolution
A change in allele frequencies over time
Define Speciation
The evolution of a new from an existing species
Define Allopatric speciation
The development of a new species via geographical isolation, which causes reproductive isolation.
Allopatric & Sympatric
Allopathic & Sympathic
Which is the correct spelling?
Allopatric & Sympatric = Correct
AllopatRIC & SympatRIC
Define Sympatric speciation
The development of a new species via random mutations, which cause reproductive isolation e.g. polyploidy
State three selection pressures
Predation, disease and competition
Describe three types of changes that can lead to reproductive isolation in a species
1) Seasonal - individuals from the same population develop different flowering or mating seasons or become sexually active at different times of the year
2) Mechanical - changes in genitalia prevent successful mating
3) Behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population
Define Genetic drift
When chance, rather than environmental factors, dictates which individuals survive, breed and pass on their alleles
How is genetic drift different to natural selection?
Natural selection:
a) Large population sizes
b) Occurs when different selection pressures can change the allele frequencies in two geographically isolated species
Genetic drift
a) Small population sizes
b) Occurs via random mutations
Why is genetic drift important only in small populations?
Chance has a greater influence on smaller populations. In larger populations, any chance variations in allele frequency tend to even out across the whole population
What is a genetic bottleneck?
When a population’s size is reduced dramatically for at least one generation
What is the Founder effect?
When a new colony is started by a few members of the original population
The small population size in the Founder effect means the colony may have:
a) Reduced genetic variation
b) Non-random sample of genes from the original population
Give an example of the Founder effect
The Amish population in America
