Genetics, populations, evolution and ecosystems

Question 1

Why may genetic variation arise?

Answer 1

• mutation (sudden change to genes or chromosomes)
• meiosis (new combinations of alleles)
• random fertilisation of gametes (new combinations of alleles which are different to parents)

Question 2

What are the environmental influences on variation?

Answer 2

• climatic conditions (temperature, rainfall, sunlight)
• soil conditions
• pH
• food availability

Question 3

What in most cases is variation due to?

Answer 3

In most cases variation is due to combined effects of genetic differences and environmental influences

Question 4

What is continuous variation?

Answer 4

e.g height, body mass

Question 5

What is discontinuous variation?

Answer 5

e.g eye colour, blood type

Question 6

What are selection pressures?

Answer 6

environmental factors that limit population of a species - predation, disease and competition. They determine the frequency of alleles within a gene pool

Question 7

What is a gene pool?

Answer 7

total number of alleles of all the genes of all the individuals within a particular population at a given time

Question 8

What factors does evolution by natural selection depend on?

Answer 8

• organisms produce more offspring than can be supported by available supply of food, light, space
• genetic variety within the populations of all species
• variety of phenotypes that selection operates against

Question 9

What does a larger population lead to in terms of genetic differences?

Answer 9

The larger the population and the more genetically varied the individuals are, the greater the chance that one or more offspring will have a combination of alleles that is advantageous for survival

Question 10

What is stabilising selection?

Answer 10

preserves the average phenotype (ones around the mean)

Question 11

What is directional selection?

Answer 11

favours phenotypes that vary in one direction from the mean (selection for extreme phenotype)

Question 12

What is disruptive selection?

Answer 12

favours individuals with extreme phenotypes rather than those around the mean

Question 13

What is allelic frequency?

Answer 13

the number of times an allele occurs in a gene pool (affected by selection)

Question 14

What are the effects of environmental changes on alleles?

Answer 14

Environmental changes affect the probability of an allele being passed on and hence the number of times it occurs in a gene pool

Question 15

What is speciation?

Answer 15

the evolution of new species from existing ones

Question 16

What is a species?

Answer 16

group of similar organisms that can breed to produce fertile offspring (members of a species are reproductively separated from another species)

Question 17

Why does genetic drift take place in small populations?

Answer 17

takes place in small populations because a small population possess a smaller variety of alleles compared to a large population

Question 18

What is genetic drift?

Answer 18

Small number of alleles in the population thus not an equal chance of each being passed on, those that are passed on will affect the whole population. This means that the population will change very quickly, making it more likely for new species to develop.

Question 19

What is allopatric speciation? + examples

Answer 19

when two populations become geographically separated by a physical barrier e.g oceans, rivers, mountains, deserts. leads to reproductive separation and formation of different species

Question 20

What is sympatric speciation? + examples

Answer 20

speciation within a population in the same area becoming reproductively separated e.g seasonal isolation (reproducing a different times of year), temporal isolation (reproduce at different times of day), behavioural isolation (different courtship patterns).

Question 21

What is a community?

Answer 21

all the populations of different species living and interacting in the same place at the same time

Question 22

What is an ecosystem?

Answer 22

Interaction between living (biotic) and non-living (abiotic) factors in a given area e.g a lake

Question 23

What is a population?

Answer 23

group of individuals of one species that occupy the same habitat at the same time and are able to interbreed.

Question 24

What is a habitat?

Answer 24

where an organism lives and this is characterised by physical conditions

Question 25

What is an ecological niche?

Answer 25

niche→ all biotic and abiotic conditions of the environment which organisms are adapted to

Question 26

What is carrying capacity?

Answer 26

maximum population size that can be maintained over a period in a particular habitat

Question 27

What are the abiotic factors that limit carrying capacity?

Answer 27

- Temperature + pH: anything but optimum can reduce population growth - Light - Water: reduced population if low water availability

Question 28

What are the biotic factors that limit carrying capacity?

Answer 28

- Interspecific competition (between different species for food, light, water) - Intraspecific competition (within the same species for food, water + breeding sites) - Predation

Question 29

What are the 2 methods that can be used to estimate the size of a population?

Answer 29

- Using quadrats and counting no of individuals in each species or percentage cover - Mark-release-recapture for moving organisms, assumes there is no death, births, migration + marking has no effect

Question 30

How is population size calculated?

Answer 30

-Population size = sample 1 size x sample 2 size / no of marked in sample 2

Question 31

What is succession?

Answer 31

variety of processes that occur over time in a species that occupy a certain area

Question 32

What occurs in primary succession?

Answer 32

progressive colonisation of bare rock/barren terrain by living organisms First the area is colonised by a pioneer species, making the abiotic factors less hostile for other species to live there Different species could be present at each stage, changing the environment so it is more suitable for other species, which changes the biodiversity Then a climax community is reached

Question 33

What is a climax community?

Answer 33

when a stable state is reached, high biodiversity and high number of new species

Question 34

What is secondary succession?

Answer 34

recolonisation of an area after an earlier community has been removed or destroyed

Question 35

What is conservation?

Answer 35

maintenance of biodiversity, between species, genetic diversity + habitats/ecosystems

Question 36

What does conservation involve?

Answer 36

Involves humans by managing community through stopping succession occurring, to save species that would become extinct by the climax community being established

Question 37

What does there need to be a balance of to maintain human resources?

Answer 37

between conservation and human needs