Topic 7: Populations And Evolution Flashcards
What is a species?
Defined as a group of similar organisms that can reproduce to give fertile offspring
What is a population?
A group of organisms of the same species living in a particular area at a particular time, so they have the potential to breed
What is the gene pool?
Is the complete range of alleles present in a pop, how often an allele occurs in pop called allele frequency
What is the Hardy-Weinberg principle?
Mathematical model that predicts the freq of alleles in a pop won’t change from one generation to the next
What are the two conditions that hardy-Weinberg principle is only true under what conditions?
It has to be a large population where there’s no immigration, emigration, mutations or natural selection
There needs to be random mating, all possible genotypes can breed with all others
What is the equation for allele frequency, in terms of hardy-Weinberg principle?
P + q = 1
What is the equation for genotype frequency, in terms of hardy-Weinberg principle?
P2 + 2pq + q2 = 1
What is the total freq of all possible genotypes for one characteristic in a certain pop?
1.0
What are the 5 ways to use hardy Weinberg principle?
Predicting allele freq
Predicting genotype freq
Predicting phenotype freq
Predicting the % of a pop that has a certain genotype
Showing if any external factors are affecting allele freq
What is variation?
The difference that exists between individuals
What is intraspecific variation?
Variation between a species, meaning that individuals in a pop can show a wide range of diff phenotypes
What is intraspecific variation cause by?
Genetic and/or environmental factors
Name 4 ways genetic variation occurs?
Same genes different alleles
Mutations
Random fertilisation
Meiosis
What is evolution?
Frequency of an allele in a pop changes over time
What is evolution caused by?
Genetic drift
Name 3 selecting pressures?
Predication, disease and competition
What are the 3 types of selection?
Stabilising, directional and disruptive selection
What is stabilising selection?
This is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
Occurring when the environment isn’t changing, and it reduces the range of possible phenotypes
What is directional selection?
This is where individuals with alleles for single extreme phenotypes are more likely to survive and reproduce, this could be a response to an environmental change
What is disruptive selection?
Where individuals with alleles for extreme phenotypes are more likely to survive no reproduce
It is the opposite of stabilising selecting as characteristics towards the middle of the range are lost
Occurring when the environment favours more than one phenotype
What is speciation?
The development of a new species from an existing species
When does speciation occur?
When populations of the same species become reproductively isolated, changes in allele frequency cause changes in phenotype, which man they can no longer interbreed to produce fertile offspring
When can reproductive isolation occur and what does it cause to happen?
When a physical barrier e.g flood divides a population of a species causing some individuals to become separated from the main population
What is geographical isolation?
When a physical event e.g. flood divides a population of a species causing some individuals to become separated from the main population
If there is so gene flow between the 2 populations what can it lead to?
Allopathic speciation
When does sympathetic speciation occur?
When a pop comes reproductively isolated without any physical separation
What will populations that are geographically separated experience ?
Experience slightly different conditions
In allopathic speciation, how do different changes in allele frequencies occur?
Different alleles will be more advantageous in different populations, so natural selection occurs. Directional selection will then act an the alleles for the key characteristics (fur length), increasing the freq of the allele for longer fur length
Allele freq will also change as mutations will occur independently in each population
Genetic drift may also affect the allele frequencies in one or both populations
Overtime leading to speciation
In allopathic speciation, what an changes in allele freq lead to?
Differences accumulating in the gene poos of the separated populations, causing change in phenotype frequencies
Eventually individuals from the different pop will have changed so much that they wont be able to breed with one another
When can sympatric speciation occur?
When random mutations within a pop prevent individuals that carry the mutation from breeding with other members of the population that don’t carry the mutation, it doesn’t involve geographical isolation
Name the 3 changes that can cause reproductive isolation?
Seasonal, mechanical and behavioural changes
What can selection pressures change?
Allele freq of a pop over time
How does genetic drift occur?
Individuals within a pop show variation in their genotypes
By chance, the allele for one genotype is passed on to more offspring than the others so the number of individuals with the allele increases
If by chance the same alleles is passed on more often again and again, it can lead o evolution as the allele becomes more common in the pop
What can genetic drift lead to?
Differences in allele freq, between to isolated populations
If enough differences in allele freq build up over time this could eventually lead to reproduction isolation and speciation
Which has a larger influence on smaller populations, evolution by genetic drift or pop size
Evolution
