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.
Define divergent evolution
Where two species that are orignally closely related become more dissimilar phenotypically over time. More likely to have homologous structures due to sharing evolutionary relationships
Define convergent evolution
where two independant species whom are distantly if related develop similar phenotypical chatacteristics due to encountering similar enivronmental and selection pressures. Tend to have analogous structures due to similar selection pressures
Define homologous structures
Organisms with structures that have a similar pattern and are similar looking, due to a common ancestor or evolutionary origin. (More than likely have different functions)
Define analogous structures
Different basic structure and look but will have the same function due to independent evolution.
Define Vestigal Structures
Organs or features of an organism that are currentyl useless
What are vestigal structures an indicator for?
A role previosuly existed for this feature in this organism for previous ancestors, therefore indicates evolution
Explain comparative embryology
Organisms can look very different in an adult stage and can look very similar in an embryo stage
-From this it can be pressumed there was a common ancestor
Explain the process of DNA hybridisation
1. DNA is removed from two species and the double strand is broken and seperated via heating
2. Seperate strands from different organisms are mixed
3. Hybrid DNA molecule is then reheated to seperate strands
What will a high temperature in DNA hybridisation indicate?
The larger the amount of temperature required the more hydrogen bonds it has, indicating that the strands are more complementary and therefore are more closely related.
What are fossils evidence of?
Where are fossils generally found?
What is sedimentary rock composed of?
mud, silt or sand
What are direct fossils?
What are indirect fossils
Not composed of any part of the original organism
What are the layers of sedimentary rock called?
What are the two forms of dating techniques?
What does relative dating technique involve
Fossils in rock strata that are closer to the surface are younger than fossils deep in strata
What are index fossils used for?
To define and identify geological periods
Age of sediments that make up rock
Sediments where they were formed in seperate locations were deposited at roughly the same time.
How old is the rocks that should be used fro carbon dating?
500,000 + years
Electron spin resonant
50,000- 500,000 years
Ideal conditions for fossilisation
-high pressure to compact sediment
Explain the process of carbon dating
-When an organism is alive the factor of carbon-14 to carbon 12 remains constant.
-When the organism dies it stops ingesting carbon therefore carbon14 will continually decay over time.
-Compare fraction of carbon 14 to 12 to determine how long ago it died
Explain the process of potassium Argon dating
-Argon 40 in rock is determined
How is genetic variation caused by sexual reproduction?
-Crossing over (recombination)
-Random assortment of chromosomes
-Combination of parents
-Combination of gametes
Example of gene flow
What is an advanage of variation
Variation within a specifes improves the chances of the species surviving the environmental change
What can selective forces be?
What populations are more like to suffer from extinction
Small inbreeding populations
Define common ancestor
An organism from which two or more species have descended.
Explain biochemical evidence in regards to evidence for evolution
-Antibody/antigen reactions can provide evidence of relationships
looking for degrees of similarity in chromosomes, amino acid sequences etc etc
Species more closely related if there are fewer differences