Genetics, Populatioms, Evolution And Ecosystems

Question 1

Genotype

Answer 1

Genetic constitution of an organism
Describes all the alleles an organism has

Question 2

Phenotype

Answer 2

The expression of the genotype and its interaction with the environment
Observable or biochemical characteristics of an organism

Question 3

Homologous chromosomes

Answer 3

In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous
There are therefore 2 loci that each carry one allele of a gene
If the alleles on each of the chromosomes is the same, then it’s homozygous
In most cases where two different alleles are present in the genotype, only one of them shows in the phenotype (dominant allele)

Question 4

Codominance

Answer 4

Two alleles both contribute to the phenotype

Question 5

Multiple alleles expression

Answer 5

As there are always only two chromosomes in a homologous pair, only 2 of the (3) alleles would be present in the organism

Question 6

Population

Answer 6

A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Any species exists as one or more populations

Question 7

Gene pool
Allele frequency

Answer 7

All the alleles of all the genes of all the individuals in a population at a given time are known as a gene pool
The number of times an allele occurs within the gene pool is the allele frequency

Question 8

Hardy- Weinberg principle

Answer 8

Provides a mathematical model/equation that can be used to calculate the frequencies of the alleles of a particular gene in a population
It predicts that the allele frequencies will not change from generation to generation

Question 9

Conditions of hardy- Weinberg principle

Answer 9

Makes the assumption that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next
No mutations arise
The population is isolated (no flow of alleles into or out of the population) (no immigration etc)
No selection (all alleles are equally likely to be passed to the next generation)
Population is large
Mating within the population is random

Question 10

Hardy weinburg equation

Answer 10

p+q=1
p^2 + 2pq + q^2=1

Question 11

Causes of variation

Answer 11

Mutation (as the primary source)
Meiosis
Random fertilisation of gametes during sexual reproduction

Question 12

Causes of differential survival and reproduction

Answer 12

Predation
Disease
Competition

Question 13

Disruptive selection

Answer 13

Favours extreme phenotypes at the expense of the intermediate phenotypes
Environmental factors takes two or more distinct forms

Question 14

Stabilising selection

Answer 14

Eliminates extremes of the phenotype range within a population
No evolutionary change
Environmental conditions constant for a long period of time

Question 15

Directional selection

Answer 15

Environmental change causes optimum phenotype to change
Some individuals (extremes/left or right of the mean) possess a combination of alleles for the new optimum for the phenotypic character
Selection pressure favours these extremes causing mean to shift

changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population, in other words, selection for one extreme phenotype

Question 16

Evolution

Answer 16

Change in the allele frequencies in a population

Question 17

New species arising from existing species

Answer 17

Reproductive separation of two populations results in the accumulation of difference in their gene pools
New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring.

Question 18

Allopatric speciation

Answer 18

Two populations become geographically separated
Prevents interbreeding
If environmental conditions either side of the barrier vary, then natural selection will influence the two populations differently and each will evolve leading to adaptions to their natural conditions.
Separate species created

Question 19

Sympatric speciation

Answer 19

Speciation within a population in the same area leading to them becoming reproductively separated

Question 20

Genetic drift

Answer 20

Occurs in small populations

the relatively few members of a small population possess a smaller variety of alleles than the members of a large population. genetic diversity is less.
As these few individuals breed, the genetic diversity of the population is restricted to those few alleles in the original population. As there are only a small number of different alleles there is not an equal chance of each being passed on. Those that are passed on will quickly affect the whole population as their frequency is high. Any mutation to one of these alleles that is selectively favoured will also more quickly affect the whole population because its frequency will be high. The effects of genetic drift will be greater and the population will change relatively rapidly, making it more likely to develop into a separate species. In large populations the effect of a mutant allele will be diluted because its frequency is far less in the much larger gene pool. The effects of genetic drift are likely to be less, and development into a new species is likely to be slower.

Question 21

Antigens are proteins, explain why a knowledge of antigens can show that animals are genetically similar

Answer 21

Protein/ antigen production determined by alleles/ genes/ base sequence of DNA
the more similar the proteins the more similar their alleles/ genes/ base sequence on DNA/ the more they are genetically similar

Question 22

Farmers are now being encouraged to replant hedges on their land
Suggest and explain one advantage and one disadvantage to a farmer of replanting hedges on the farmland

Answer 22

Greater diversity so increase in predators of pests so more yield/ income/ less pesticides/ less damage to crops
Increase in pollinators so more yield/ income
May attract more tourists to their farm so more income
Reduced land area for crop growth/ income
Greater diversity so increase pest population so less yield/ income/ more need for pesticides/ more damage to crops

Question 23

Intraspecifc competition

Answer 23

Individuals of the same species compete with one another
It is the availability of resources that determines the size of the population
Equally matched

Question 24

Interspecific competition

Answer 24

Individuals of different species compete for resources
When populations of 2 species are in competition, one will normally have a competitive advantage over the other. The population of this species will gradually increase in size while the population of the other will diminish
Resources available to each population reduced
both populations will be limited by a lower amount of food. They’ll have less energy for growth and reproduction, so the population sizes will be lower for both species.

Question 25

Competitive exclusion principle

Answer 25

If conditions remain the same (intraspecific competition) this will lead to the complete removal of one species

This principle states that where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other.

no two species can occupy the same niche indefinitely when resources are limiting.

Question 26

Relationship between predator and prey

Answer 26

Predators eat their prey, thereby reducing the population of prey.
• With fewer prey available the predators are in greater competition with each other for the prey that are left.
• The predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce.
• With fewer predators left, fewer prey are eaten and so more survive and are able to reproduce.
• The prey population therefore increases.
• With more prey now available as food, the predator population in turn increases.

Question 27

Niche

Answer 27

Specific role an organism has in its habitat
The niche a species occupies includes its biotic(what it eats and is eaten by) and abiotic interactions (the temperature range an organism can live in, the time of day when an organism is active)

Question 28

Population size

Answer 28

Total number of organisms of one species in a habitat
Influenced by abiotic and biotic factors

Question 29

Types of competition

Answer 29

Chemical
Consumptive
Encounter
overgrowth
Territorial

Question 30

Chemical competition

Answer 30

Production of toxin or deterrent chemical to exclude competitors

Question 31

Consumptive competition

Answer 31

Competitive use of resource eg food

Question 32

Encounter competition

Answer 32

Physical defence of resource

Question 33

Overgrowth competition

Answer 33

Overwhelms in size or number

Question 34

Territorial

Answer 34

Defence of territory, breeding, feeding areas

Question 35

Predation

Answer 35

Predator eats prey
Population sizes of each are interlinked (one change causes other to change)

Question 36

Intraspecific competition graph

Answer 36

causes a cyclical change in population size around the ecosystem’s carrying capacity — where the population grows, shrinks, grows again and so on. This is because the population of a species increases when resources are plentiful. As the population increases, there’ll be more organisms competing for the same amount of space and food. Eventually, these resources become limiting. If the population grows beyond the carrying capacity, there won’t be enough resources for all the organisms and the population will begin to decline.
A smaller population then means that there’s less competition for space and food, which is better for growth and reproduction — so the population starts to grow again.

Question 37

Ecosystem

Answer 37

all the organisms living in a community, plus all the abiotic conditions in the area in which they live

Question 38

Adaptation

Answer 38

a feature that members of a species have that increases their chance of survival and reproduction. These features can be physiological (processes inside their body), behavioural (the way an organism acts) or anatomical (structural features of their body)
Every species is adapted to use a species in a way no other species can (specific niche)

Question 39

Lek

Answer 39

Group of males cooperating for a period of time to overthrow stronger individual

Question 40

Mechanisms to diffuse confrontation

Answer 40

Size, colouration
(Eg alpha gorillas being silverback)

Question 41

Dispersal

Answer 41

Method to reduce competition
Dispersing away from an area of high population density
Also avoids costs of inbreeding
But have to fund suitable habitat with low population density

Question 42

Succession

Answer 42

Ecosystems change day to day as populations fluctuate
Succession describes these changes over time in the species that occupy a particular area
Occurs in a series of stages
Can make environment less hostile

Question 43

Stages of succession

Answer 43

At each new stage new species colonise the area and these may change the environment
The changes may make to less suitable for the existing species (so new species out competes them)
Changes may make it more suitable for other species with different adaptions

Question 44

Effect of successional changes

Answer 44

Alter abiotic environment
Can result in a less hostile environment so easier for species to survive, so new communities formed and biodiversity may be changed

Question 45

Pioneer species

Answer 45

Colonise an inhospitable environment
Make up a pioneer community

Question 46

Features of pioneer species that make them well suited to the inhospitable environment

Answer 46

Asexual reproduction (single organism can rapidly multiply to build up a population)
Production of vast quantities of wind dispersed speeds/spores so they can easily reach isolated situations
Rapid germination of seeds on arrival
Ability to photosynthesise (use of light due to lack of other food sources so not dependent on animal species)
Ability to fix nitrogen from the atmosphere (even if there is soil there is few or no nutrients)
Tolerance to extreme conditions

Question 47

Climax community

Answer 47

Remain more or less stable over a long period of time
Stable state comprises a balanced equilibrium of species with few new species replacing those that exist
Lots of biodiversity
In a stable equilibrium with the prevailing climate

Question 48

5 common features emerging from succession

Answer 48

Abiotic environment becomes less hostile
Greater variety of habitats and niches (due to the above)
Increases biodiversity (due to above)
More complex food webs
Increased biomass (due to the above)

Question 49

Stages of succession from spec

Answer 49

At each stage in succession, certain species may be recognised which change the environment so that it becomes more suitable for other species with different adaptations. The new species may change the environment in such a way that it becomes less suitable for the previous species.

Question 50

Examples of abiotic environment becoming less hostile

Answer 50

Soil forms: retains water
Nutrients more plentiful
Plants provide shelter from wind

Question 51

Biodiversity changes throughout succession

Answer 51

Increases to peak in mid succession then decreases as the climax community is reached because dominant species out compete pioneer and other species , eliminating them from the community

Question 52

What determines dominant species in a community

Answer 52

Abiotic factirs such as climate

Question 53

Secondary succession

Answer 53

Land that has already sustained life is altered
(Eg due to land clearance or forest fires)
Ecosystem rapidly returns to climax community
Because the land has been altered in some way, some of the species may be different