Variation and Evolution Flashcards
Why do organisms differ in their phenotype?
Different genotypes.
Same genotype different epigenetic modification Different environments.
What is continuous variation?
It is controlled by a number of genes. Character shows a gradation from one extreme to another.
Give examples of continuous variation
Human height, number of leaves, eye colour and body mass.
What is discontinuous variation?
It’s controlled by a single gene with characters having a clear cut.
Give examples of discontinuous variation
Number fingers, sex, tongue rolling ability, mammary glands
What is heritable variation?
Results from genetic changes due to sexual reproduction,
When can heritable variation occur?
Mixing two different parental genotypes and cross fertilisation random assortment of homologous chromosomes in metaphase I.
Crossing over between homologous chromosomes during prophase I.
Random assortment of chromatids and metaphase II.
What do genetic changes do?
They establish new allele combinations only mutations generate novel and lasting variations.
What is non-heritable variation?
Environmental influences that determine phenotypic variation (not inherited)
Give examples of non inheritable variation?
Diet, exercise
Light, temp, availability of inorganic ions.
Give examples of interactions between genotype and environment
Himalayan rabbit ears: if skin tempo falls below 25 degrees genes will produce melanin pigment, the body extremities turn on.
Hydrangae flower colour: acidic soils cause blue flowers, aluminium is more soluble at acidic pH and binds to anthocyanin pigments turning them blue.
What limits a population?
Competition human and environmental factors play selective pressures on survival of different phenotypes and hence breeding success.
What is interspecific competition?
Competition between individuals of DIFFERENT species i.e. predator prey relationships.
What is intraspecific competition?
Competition between individuals of the SAME species basis of the origin of species by natural selection.
What is a gene pool?
All the alleles, of all the genes, of all the individuals within a population at one time.
What is allele frequency?
A measure of the relative frequency of an allele on a locus of a population.
What happens to the gene pool if the environment changes?
Some phenotypes are more advantageous and will be selected for whilst others will be disadvantaged and selected against. Overtime the gene pool changes with some of their alleles being more frequent than others.
What does selection pressure affect?
The allele frequency within a gene pool
What is selection?
It is the process at which better adapted organisms are able to survive and reproduce with less adapted organisms unable to do so.
The better adapted the organism the more likely they are to pass on their characteristics to succeeding generations.
What happens to the gene pool if the environment stays remain stable?
The gene pool remains stable
What are selective agents?
Food supply, breeding sites, climate and human impact
What does a selection pressure do?
Determines the allele frequency within a gene pool. It can affect the survival of different phenotypes in a population i.e. selective predation, camouflage, mimicry.
Only individuals who survive to reproduce are able to pass on advantageous alleles to their offspring and change the allele frequency over time.
What are the hardy Weinberg equations?
p + q = 1
p^2 +2pq + q^2 = 1
What do all the letters indicate in the hardy Weinberg principle?
p = frequency of allele (A) q = frequency of allele (a) p^2 = frequency of homozygous dominant (AA) q^2 = frequency of the homozygous recessive (aa) 2pq = frequency of heterozygotes
What does the hardy Weinberg principal state?
That the frequency of dominant and recessive alleles remain constant from one generation to the next if the following conditions are met. It only takes one generation of meeting the conditions to bring it into equilibrium this population will remain in equilibrium as long as the conditions are met.
What are the conditions for the hardy Weinberg principle?
Large population – 100+
No selection for or against any phenotype
Random meeting throughout the population
No new mutations
Population is isolated – no immigration or emigration.
What won’t occur if the conditions under which the hardy Weinberg principle applies don’t change?
Evolution in terms of speciation
What is natural selection?
When better adapted organisms survive they are able to reproduce producing successful offspring survival of the fittest.
What are the steps in natural selection?
- Variation in a population is due to mutation
- Theres a selection pressure
- Individuals with the advantageous alleles are more likely to survive and reproduce
- They pass on the advantageous alleles to the next generation.
- Over many generations the advantageous allele will become more common in a population.
How to layout a exam question for NS:
Variation in … due to RANDOM MUTATIONS in the population.
These individuals have a SELECTIVE ADVANTAGE, state why….
Survive to REPRODUCE
Pass on the ADVANTAGEOUS ALLELES to the next generation.
Over many generations the allele frequency increases in the population (one population is no longer able to successfully reproduce with another population i.e behavioural)
What is a population?
A group of organisms of the same species which reproduce with each other.
What is genetic drift?
Describes how allele frequency fluctuates unpredictably from one generation to the next, reduces genetic variation. Accident and random nature.
What is the biological species concept?
A group of similar individuals which are able to interbreed and produce fertile offspring and is reproductively isolated from other such groups
What is speciation?
The evolution of two different species from an existing
What is meant when a species is spectiated?
When two species become too genetically distinct
When our populations reproductively isolated?
If there’s no mixing of genes between them
Why can speciation occur?
Genetic drift in isolated populations.
The founder effect of disproportionate allele frequencies in small populations which can cause the equilibrium of the gene pool to change.
Natural selection.
What is the founder effect?
When the population is isolated on an island or new habitat the founding members of the population are a small sample of the original population.
By chance they have different allele frequencies to the original population and if the population remain small it may undergo genetic drift. If the populations are genetically distinct enough they won’t be able to breed and produce fertile offspring.
What is the bottleneck?
It’s resulting from a disaster which reduces the population size i.e. earthquakes. These populations may survive after being squeezed through a bottleneck of low numbers.
What is alopatric isolation?
The formation of two spaces from an original one due to geographical isolation.The population becomes physically split into separate demes
What are common barriers barriers to gene flow
rivers, mountain ranges and deserts
These populations will evolve independently to each other to the environmental conditions where they live. Two populations may start to diverge and develop other mechanisms to keep them reproductively isolated, should they meet again.
What is sympatric speciation?
The formation of two species from one original species due to reproductive isolation whilst occupying the same geographical location.
What are the type of barriers?
Temporal/seasonal isolation behavioural isolation mechanical isolation gamete isolation hybrid unviability hybrid sterility
What is temporal/seasonal barriers?
When breeding time/season or time of activity of two closely related populations don’t correspond.
What is behavioural isolation?
Courtship displays
Morphological mechanical isolation is
Not being able to physically mate is genitals are incompatible.
Hybrid sterility is?
One set of chromosomes differ from each parent so can’t pair up in meiosis one and produce gametes (meiosis fails and no gametes can be produced as chromosomes in prophase one can’t pair up as they aren’t homologous)
What does it mean when a plants can become polyploid?
The Kromozone set doubles as the chromosomes compare up in meiosis making fertile new species.
What is hybrid unviability?
When fertilisation can occur but an embryo can’t develop as they don’t have chromosomes which match up (not homologous).
What do all mechanisms for speciation result in?
A group of organisms being prevented from interbreeding, resulting in a lack of gene flow. Different selection pressures can be exerted on the group of individuals leading to a differ in allele frequency which leads to new species being created.
What can evolution evolution be brought by?
Mutation, gene flow, genetic drift, natural selection
Describe Darwin’s theory?
Competition for limited resources and those individuals with alleles that produce a better adaptive phenotype reproduce more successfully. They pass alleles produced to the offspring which continues over generations these alleles have an increase in proportion. The average phenotype changes – evolution. If the changes are significant enough an organism may be no longer able to interbreed successfully with a representative of the original population so a new species has formed. Natural selection maintains phenotypes in a stable environment and changes them in a changing environment.
