Chapter 18 - Populations And Evolution Flashcards
What are the assumption of the hardy Weinberg principle
No mutations occur.
There is no migration into or out of the population.
Mating is random.
The population size is large.
There are no natural selection pressures.
What is the gene pool
all alleles of all genes in all individuals of a population at a given time
Hardy Weinberg equations
p + q = 1
p^2 + q^2 + 2pq = 1
Sources of genetic variation
1) Mutations - Changes to genes and chromosomes that may be passed on to the next generation.
2) Meiosis - New combinations of alleles are present in the gametes formed, produced by independent assortment of chromosomes and crossing over between chromatids.
3) Random fertilisation - Random fertilisation of gametes produces new combinations of alleles in a zygote.
4) Random mating
Environmental factors that can cause variation
1) Light
2) Nutrient and food availability
3) Temperature
4) Rainfall
5) Soil conditions
6) pH
What are polygenes
These are different genes at different loci that all contribute to a particular aspect of phenotype.
What is environmentally variation
Environmental variation is variation caused by the environment in which an organism lives.
What is genetic variation
Genetic variation is variation due to the genes and alleles an individual possesses.
What is genetic variation
Genetic variation is variation due to the genes and alleles an individual possesses.
Conditions for student t test
The data must be continuous and normally distributed.
The variances of the populations should be equal.
The samples must be independent of each other.
What does the student t test do
determine if there is a significant difference between the mean values of a particular variable across two populations.
Examples of selection pressures
Predation
Competition for resources
Climate change
Disease
How can variation drive evolution
1) It generates a range of phenotypes within a population, enhancing the likelihood that some individuals will have alleles for advantageous traits.
2) Individuals with these beneficial traits are more likely to survive and reproduce under changing conditions, transmitting the advantageous alleles to their offspring.
3) Natural selection occurs.
Types of natural selection and how they affect phenotypes
- Directional selection - Selects for one extreme phenotype over other phenotypes.
- Stabilising selection - Selects for the average phenotype and selects against extreme phenotypes.
- Disruptive selection - Selects for extreme phenotypes and selects against the intermediate phenotype, especially when an environmental factor takes two or more distinct forms.
How does the different types of selection effect allele frequency
Directional - Increases allele frequency for one extreme phenotype
Stabilising - Increases allele frequency for the average phenotype, decreases allele frequency for extremes
Disruptive - Increases allele frequency for multiple extreme phenotypes, decreases allele frequency for intermediates
How do the different types of selection affect the normal distribution curve
Directional - Shifts curve in the direction of the favoured extreme
Stabilising - Narrows the curve
Disruptive - The curve shifts into multiple peaks either side of where the average phenotype peak was
What are selection pressures
environmental factors that affect their survival and reproductive success.
What are species
a group of individuals that are capable of breeding with one another to produce fertile offspring.
What are similar and different between individuals of the same species
Similar - genes
Different - alleles
What is speciation
Speciation is the process by which new species are formed.
What causes speciation
- Reproductive isolation of populations, which is the inability of two groups of organisms to breed with one another.
- Genetic divergence, driven by natural selection and genetic drift.
What is genetic drifts
the random changes in allele frequencies within a population’s gene pool, due to random chance (not as a result of natural selection)
What is adaptive radiation
where organisms DIVERSIFY rapidly from an ancestral species into a wide array of new forms, each adapted to a specific ecological niche
When does adaptive radiation occur
It is more likely to occur when a change in the environment makes new resources available.
What is reproductive isolation
when populations cannot interbreed successfully to produce viable, fertile offspring.
What is genetic isolation
a lack of gene flow between populations due to reproductive barriers so organisms cannot interbreed successfully
What can reproductive isolation lead to
- genetic isolation
What causes reproductive isolation
prezygotic barriers or postzygotic barriers
What do Prezygotic reproductive barriers do
These prevent fertilisation and the formation of a zygote, and act before the fertilisation of an egg cell
What do Postzygotic reproductive barriers do
These are often a result of hybridisation between different species.
They produce infertile offspring, reducing their reproductive potential
Two types of speciation
allopatric speciation and sympatric speciation
What happens in Allopatric speciation
1) Some members of a population are geographically separated from the rest by a physical barrier like mountains, rivers, or seas.
2) Geographical separation exposes distinct parts of the population to different environmental pressures.
3) These prezygotic reproductive barriers lead to reproductive isolation.
4) Reproductive isolation interrupts gene flow, and the physical separation leads to genetic divergence.
5) This causes the populations to evolve separately and form separate species.
What happens in Sympatric speciation
1) Speciation takes place within the same geographical location.
2) Ecological or behavioural separation mechanisms like different habitat preference, mate selection, lead to the groups becoming reproductively isolated.
3) Reproductive isolation interrupts gene flow, and the physical separation leads to genetic divergence.
4) This causes the populations to evolve separately and form separate species.
Know to how to do genetic crosses
