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Flashcards in Variation and evolution Deck (40):

What is variation?

Variation is the driving force behind natural selection.


What is continuous variation?

Controlled by a number of genes. The environment is also affecting the phenotype of the organism. The characteristic shows a gradation from one extreme to another.
Characteristics are controlled by many genes and are described as polygenic.


What is discontinuous variation?

Each characteristic controlled by a single gene , it is monogenic. It is categoric as characteristics are clear cut and fit into one of several categories which are easy to tell apart.
The phenotype is not affected by the environment.


What is heritable variation?

This results from genetic changes due to sexual reproduction and the formation of gametes and is passed into offspring by:
- mixing of 2 different genotypes in cross fertilisation.
- Random assortment of homologous chromosomes.
- Crossing over between chromosomes.


What is non-heritable variation?

Caused by environmental influences that alter phenotype.
- diet and exercise.
- Plants; temp, light.
Organisms of identical genotypes with different environments, they show considerable variety, responsible for continuous variation in a population.


Interaction between genotype and environment?

Himalayan rabbit ears= if skin temp falls to 25, genes which produce melanin pigment at body extremities.
Hydrangea flower colour= Acid soils cause blue flowers as aluminium is more soluble at acid PH and binds to anthocyanin pigments.


What is inter-specific competition?

Competition between individuals of different species. Illustrated by predator-prey relationships.


What is intraspecific competition?

Competition between individuals of the same species. The 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 in a population at any one time.
It remains stable over time if the environment is stable.


What is an allele frequency?

A measure of how often an allele appears in the gene pool of a population.


What is evolution?

The change in organisms over many generations. It can give rise to new species from pre-existing ones (darwins finches).


What is adaptive radiation?

The evolution of a number of species from a common ancestor.


What happens if the environment changes?

Some phenotype will be more advantageous and will be selected for, whilst others will be disadvantageous and be selected against.


What is selection pressure?

The process by which organisms better adapted (selective advantage, beneficial allele) to their environment survive and breed, while those less well adapted fail to do so.
The environment exerts the selection pressure and this determines the spread of the allele within the gene pool.


The theory of natural selection??

Variation in all populations, in a changing environment some individuals have advantages.
Individuals have the potential to produce larger number of offspring (overproduction).
Number of adults tends to remain constant (carrying capacity).
As a result, struggle for survival (intraspecific), only the fittest survive.
These survive and reproduce passing on advantageous allele to offspring.
Over time, allele frequency of population will change.
If environment keeps changing N.S will continue.


What is stabilising selection?

If the environment is stable then the extreme variations tend to be eliminated (e.g. head size at birth).


What is directional selection?

If the environment changes to favour one extreme of the phenotype (decrease temp-fur length).


What is disruptive selection?

Where the two extremes are selected for at the same time. If these two genes are isolated a new species could result.


What are antibiotics?

Molecules which kill or inhibit the growth of bacteria, they are produced by saprotrophic fungi as a weapon for inter specific competition.


How are they left at low levels in the environment?

They have been added routinely to animal feeds in intensive farming.
They may be added to hand washes.
People may not finish a prescribed course.


The rise of super bugs?

Bacteria can pass on genes for resistance to antibiotics carried on plasmids. They can pass plasmids on during binary fission and to other bacterial cells by conjugation tube (pilus), gene resistance quickly spreads.

Bacteria reproduce rapidly and therefore random mutation quickly led to resistant strains.


The development of antibiotic resistance?

Any bacteria will show genetic variations in their resistance to antibiotics. (could be mutation or passed during reproduction).
Ones without resistance are killed, ones with survive to pass on resistant allele.
Acts as selective pressure!!
Leads to multi drug resistant bacteria. (MRSA).


Warfarin resistance in rats??

Warfarin is an anticoagulant used to poison rats (and treat people with blood clots).
An allele for resistance (R) to warfarin exists through random mutation- allele is co dominant.
R= resistance to warfarin, high requirement for vit K.
N= does not give resistance, not a high demand for vit K.
This is heterozygote advantage (RN).
RR dies as massive need for vit K.
NN dies due to warfarin.
RN survive to reproduce as have resistance to warfarin but a low vit K.
Warfarin acts as a selective pressure, change in allele frequencies.


What is insecticide resistance?

Insect pests have developed insecticide resistance as they have been over used.
Same steps occur as during natural selection.


What is genetic drift?

Chance variations in allele frequencies in a population.


Genetic drift explained??

Allele frequencies can just change due to chance and not ad and disadvantageous. Occurs in a small, isolated population, by chance they may have a reduced genetic diversity so different allele frequencies in their gene pool. Leads to larger differences in phenotype between old and new called founder effect.
By chance if some wiped out the rest may have very different allele frequency to original so reduction in number of alleles (reduced genetic diversity).


Genetic bottleneck can cause genetic drift. What is it?

Where a natural disaster causes a random and severe change in allele frequency of populations gene pool. (by killing loads of them and wiping out their alleles in gene pool).


What is speciation?

The formation of new species and occurs when two groups of organisms (same population) can no longer breed together (reproductive isolated) to produce fertile offspring and so are two different species.


Overview of reproductive isolation!

When resulting groups of organisms are prevented from interbreeding.
Result is a lack of gene flow between groups.
Different selection pressures may be exerted on group of organisms, leading to different allele frequencies occurring in each group during NS.
This can lead to new species called speciation.


What is allopatric speciation?

Occurs when populations that could once interbreed are reproductively isolated by being geographically separated (geographical isolation) into two groups.
Mountains, rivers, even a road may separate populations of same species, these species will evolve and undergo NS due to selection pressures and alleles. Over time develop different gene pools.


What does demes mean?

Where the population becomes physically split into separate breeding groups.


What is sympatric speciation?

Occurs when organisms inhabiting the same area become reproductively isolated into two groups where the barriers are not physical ones.
Barriers could include:
temporal or seasonal isolatio
behavioural isolational.
Mechanical isolation.
Gamete isolation.
Hybrid inviability.
Hybrid sterility.


What is seasonal isolation?

When two populations of a species become reproductively isolated because they mate at different times of the year. Therefore, will not produce offspring with one another and may eventually become to separate species.


What is temporal isolation?

When the two populations become reproductively isolated because they are active at different times of day (time).


What is behavioural isolation?

A population of the same species become reproductively isolated due to variations in courtship and mating behaviour (such as complex calls, dances and rituals).


What is mechanical or morphological isolation?

This reproductive isolation within a population of the same species is caused by variation in the sexual organs which can lead to some being unable to mate successfully with others.


What is hybrid sterility?

Fertilisation occurs but hybrid organism is formed, but it is sterile because it has an odd number of homologous chromosomes. Unable to pair up during meiosis I, gametes cannot form.


What is hybrid inviability?

Fertilisation occurs however the embryo is unable to develop into a living organism. Mating occurs and a hybrid is produced, but it does not develop at all or typically dies early.


What does hybrid mean?

Offspring between two different species.


What is inviability?

An organism that does not thrive.