Flashcards in Population Genetics/Evolution Deck (61)
Define a population
A population is a group of organisms of the same species living in a specific region at a given time
Organisms are of the same species if they can breed to produce fertile offspring
Different subspecies like a race can exist with the same species producing fertile offspring.
Types of variation
Formula for phenotype
genotype x environment
Despite phenotype being altered by environemntal pressures what remains the same?
Population is on which there exists only one variant of a trait
Population is on which there exists more than one variant of a trait
Define Continuous Variation
Where there are an infinite number of variants along a spectrum
Define Discontinious variation
When there are a discrete and finite number of variants.
List the causes of genetic variation
1. Sexual Reproduction
Explain how sexual reproduction contributes to geentic varation
a) crossing over to form recombinant genetical material
b) random assortment of chromsomes into gametes
c) combination of parents
d) combination of gametes at fertilisation`
Define gene pool
A sum and aggregation os all the alleles in all organisms for a particular population.
Define gene flow
Arrival of new individuals therefore new genes or alleles into a population therefore added to the gene pool.
What is essential for migration to affect allele frequency and the gene pool.
Requires the reproduction between individuals of different populations
Changes in allele frequencies that are unpredictable due to chance events.
Explain the bottle neck effect
Allele frequencies experience a sudden drop in population size i/e from a natural disaster. Allele frequencies drastically change in one go.
Surviving population is not nesscarily a representation of the orginal population.
Explain the founder effect
A group of individuals have emigrated from a larger population and have colonised and begun a new population. New population will be small
What does the enivronment select?
The favourable phenotype
Inherited characteristics that increases chance on surivial
Define the process of natural selection
Involves the result in the surivival of the fittest organism that is best adapted to the environment and selective pressures.
Outline the steps in natural selection
1. Phenotypic variation must exsist within the population
2. In a changing environment one phneotype will be favoured. That phenotype will have an improved chance at surviving and reproducing.
3. Therefore more offspring will obtain favoured characteristics
4. Frequency of favoured alleles within the population will increase across generations.
Define selective advantage
A characteristic of an organism that enables it to survive and reproduce better than of others in the environment.
Define Artifical Selection
Humans select and breed organisms of their choice to obtain desireable features in the offspring.
Process by which over geological time, the heritable traits of the individuals of a population chance, leading to the advent of new species from previously exsisting species.
Define Allopatric speciation
Whereby a new species is formed due to the geographical isolation of two populations of the same species.
Explain the steps in speciation
1. A geographical barrier must occur which seperate the population and cause gene flow to cease.
2. Different selection pressures on either side
3. Changes in the phenotypic characteristics in the populations are such that if the two populations where brought together they would unable to produce fertile offpsring. Hence new species has been formed
A species is said to be extinct when there are no members of that species left alive
Why does extinction occur most of the time?
Due to their being very few or no organisms that can adapt to a new selection pressure.