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A Level Biology > Genetics, Populatioms, Evolution And Ecosystems > Flashcards

Genetics, Populatioms, Evolution And Ecosystems Flashcards

1
Q

Genotype

A

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

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2
Q

Phenotype

A

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

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3
Q

Homologous chromosomes

A

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)

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4
Q

Codominance

A

Two alleles both contribute to the phenotype

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5
Q

Multiple alleles expression

A

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

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6
Q

Population

A

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

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7
Q

Gene pool
Allele frequency

A

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

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8
Q

Hardy- Weinberg principle

A

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

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9
Q

Conditions of hardy- Weinberg principle

A

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

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10
Q

Hardy weinburg equation

A

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

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11
Q

Causes of variation

A

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

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12
Q

Causes of differential survival and reproduction

A

Predation
Disease
Competition

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13
Q

Disruptive selection

A

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

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14
Q

Stabilising selection

A

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

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15
Q

Directional selection

A

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

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16
Q

Evolution

A

Change in the allele frequencies in a population

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17
Q

New species arising from existing species

A

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.

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18
Q

Allopatric speciation

A

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

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19
Q

Sympatric speciation

A

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

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20
Q

Genetic drift

A

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.

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21
Q

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

A

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

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22
Q

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

A

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

23
Q

Intraspecifc competition

A

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

24
Q

Interspecific competition

A

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.

25
Competitive exclusion principle
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.
26
Relationship between predator and prey
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.
27
Niche
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)
28
Population size
Total number of organisms of one species in a habitat Influenced by abiotic and biotic factors
29
Types of competition
Chemical Consumptive Encounter overgrowth Territorial
30
Chemical competition
Production of toxin or deterrent chemical to exclude competitors
31
Consumptive competition
Competitive use of resource eg food
32
Encounter competition
Physical defence of resource
33
Overgrowth competition
Overwhelms in size or number
34
Territorial
Defence of territory, breeding, feeding areas
35
Predation
Predator eats prey Population sizes of each are interlinked (one change causes other to change)
36
Intraspecific competition graph
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.
37
Ecosystem
all the organisms living in a community, plus all the abiotic conditions in the area in which they live
38
Adaptation
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)
39
Lek
Group of males cooperating for a period of time to overthrow stronger individual
40
Mechanisms to diffuse confrontation
Size, colouration (Eg alpha gorillas being silverback)
41
Dispersal
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
42
Succession
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
43
Stages of succession
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
44
Effect of successional changes
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
45
Pioneer species
Colonise an inhospitable environment Make up a pioneer community
46
Features of pioneer species that make them well suited to the inhospitable environment
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
47
Climax community
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
48
5 common features emerging from succession
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)
49
Stages of succession from spec
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.
50
Examples of abiotic environment becoming less hostile
Soil forms: retains water Nutrients more plentiful Plants provide shelter from wind
51
Biodiversity changes throughout succession
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
52
What determines dominant species in a community
Abiotic factirs such as climate
53
Secondary succession
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

A Level Biology (23 decks)

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