Variation and evolution

Question 1

What is variation?

Answer 1

Variation is the driving force behind natural selection.

Question 2

What is continuous variation?

Answer 2

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.

Question 3

What is discontinuous variation?

Answer 3

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.

Question 4

What is heritable variation?

Answer 4

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.

Question 5

What is non-heritable variation?

Answer 5

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.

Question 6

Interaction between genotype and environment?

Answer 6

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.

Question 7

What is inter-specific competition?

Answer 7

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

Question 8

What is intraspecific competition?

Answer 8

Competition between individuals of the same species. The basis of the origin of species by natural selection.

Question 9

What is a gene pool?

Answer 9

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.

Question 10

What is an allele frequency?

Answer 10

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

Question 11

What is evolution?

Answer 11

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

Question 12

What is adaptive radiation?

Answer 12

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

Question 13

What happens if the environment changes?

Answer 13

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

Question 14

What is selection pressure?

Answer 14

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.

Question 15

The theory of natural selection??

Answer 15

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.

Question 16

What is stabilising selection?

Answer 16

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

Question 17

What is directional selection?

Answer 17

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

Question 18

What is disruptive selection?

Answer 18

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

Question 19

What are antibiotics?

Answer 19

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

Question 20

How are they left at low levels in the environment?

Answer 20

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.

Question 21

The rise of super bugs?

Answer 21

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.

Question 22

The development of antibiotic resistance?

Answer 22

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).

Question 23

Warfarin resistance in rats??

Answer 23

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.

Question 24

What is insecticide resistance?

Answer 24

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

Question 25

What is genetic drift?

Answer 25

Chance variations in allele frequencies in a population.

Question 26

Genetic drift explained??

Answer 26

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).

Question 27

Genetic bottleneck can cause genetic drift. What is it?

Answer 27

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).

Question 28

What is speciation?

Answer 28

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.

Question 29

Overview of reproductive isolation!

Answer 29

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.

Question 30

What is allopatric speciation?

Answer 30

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.

Question 31

What does demes mean?

Answer 31

Where the population becomes physically split into separate breeding groups.

Question 32

What is sympatric speciation?

Answer 32

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.

Question 33

What is seasonal isolation?

Answer 33

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.

Question 34

What is temporal isolation?

Answer 34

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

Question 35

What is behavioural isolation?

Answer 35

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

Question 36

What is mechanical or morphological isolation?

Answer 36

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.

Question 37

What is hybrid sterility?

Answer 37

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.

Question 38

What is hybrid inviability?

Answer 38

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.

Question 39

What does hybrid mean?

Answer 39

Offspring between two different species.

Question 40

What is inviability?

Answer 40

An organism that does not thrive.