3.7

Question 1

What is the term genotype

Answer 1

Genetic constitution of an organism

Question 2

What is meant by the term phenotype

Answer 2

The expression of the genotype and its interactions with the environment

Question 3

What are alleles and how do they arise

Answer 3

Variations of a particular gene arises by mutation

Question 4

How many alleles of a gene can be found in a diploid organism

Answer 4

2 as diploid have 2 sets of chromosome

Question 5

Describe different type of alleles

Answer 5

Dominant:always expressed
Recessive: only expressed when homozygous recessive
Codominat: both alleles expressed

Question 6

What is meant by homozygous and heterozygous

Answer 6

Homozygous alleles at a specific locus are the same
Heterozygous alleles at a specific locus are different

Question 7

What do monohybrid and dihybrid crosses show

Answer 7

Mono- inheritance of one specific phenotype coded by single gene
Di- inheritance of two phenotypes by two different genes

Question 8

What is sex linkage

Answer 8

A gene with a locus on a sex chromosome

Question 9

Explain why males are more likely to express a recessive x linked allele

Answer 9

Males only having one X so only need one recesssive alleles to have that phenotype whereas women have two X

Question 10

Explain how autosomal linkage affects inheritance of alleles

Answer 10

Two genes located on the same non sex chromosome
So the alleles are inherited together
But crossing over can create a new combination of alleles.

Question 11

What is epistatis

Answer 11

Interaction of non linked genes where one suppresses the other

Question 12

Describe when a chi squared test could be used

Answer 12

When determining if observed results are significantly different from expected results
Data has to be catigorical

Question 13

Suggest why in genetic crosses the observed phenotypic ratio is not the same as expected

Answer 13

Fertilisation is random
Acutosomal linkage
Epistatis
Sex linkage
Not representative sample
Some genotypes cause death

Question 14

Describe how chi squared can be calculated

Answer 14

Sum of the square root of the observed value minus the expected divided but the expected

Question 15

Describe how a chi squared can be analysed

Answer 15

Number of degrees of freedom- number of catagories
Determine critical value
If X2 is greater the difference of significant and reject the null so less than 5% probability that the results are due to chance

Question 16

What is a population

Answer 16

A group of organisms of the same species in a particular space at a particular time
That can potentially interbreed

Question 17

What is a gene pool

Answer 17

All the alleles of all the genes in a population at one time

Question 18

What is allele frequency

Answer 18

Proportion of an allele of a gene pool

Question 19

What does the hardy-Weinberg principle state and what are the conditions under which the principle applies

Answer 19

Allele frequency will not change from generation to generation given:
Population is large
No immigration
No mutations
No selection
Mating is random

Question 20

What is the hardy Weinberg equation

Answer 20

P^2+2pq+q^2=1 which can be used with p+q=1

Question 21

Explain why individuals within a population of a species may show a wide ramage of variation in a phenotype

Answer 21

Genetic factors
Mutations
Crossing over
Independent segregation
Random fertilisation
Environmental factors

Question 22

What is evolution

Answer 22

Change in allele frequency over time occurring through natural selection

Question 23

Describe factors that may drive natural selection

Answer 23

Predation, diseases, and competition
These result in differential survival and reproduction

Question 24

Explain the principles of natural selection in the evolution of population

Answer 24

Mutation, advantage, reproduction, inheritance, allele frequency

Question 25

Explain the effects of stabilising selection

Answer 25

Organism with alleles coding for average variation of a trait have an advantage So frequency of allele coding for average variation of a trait increase So range is reduced

Question 26

Explain the effects of directional selection

Answer 26

Organisms with alleles coding for one extreme va Faustino of a trait have a selective advantage do frequency of extreme allele increases and other alleles decrease

Question 27

Explain the effects of disruptive selection

Answer 27

Organisms with alleles coding for extreme variation have a selective advantage So frequency of allele increases and average decreases. This can lead to speciation

Question 28

Describe speciation

Answer 28

Reproductive separation of two populations Can result in accumulation of differences in their gene pools New species arise when these genetic differences lead to an inability of the population to inyerbreeed and produce fertile offspring

Question 29

Describe allopatric speciation

Answer 29

Population is split due to geographical isolation (eg. new river formed) This leads to reproductive isolation, separating gene pools by preventing interbreeding / gene flow between populations Random mutations cause genetic variation within each population Different selection pressures / environments act on each population So different advantageous alleles are selected for / passed on in each population So allele frequencies within each gene pool change over many generations Eventually different populations cannot interbreed to produce fertile offspring

Question 30

Describe sympatric speciation

Answer 30

Population is not geographically isolated Mutations lead to reproductive isolation, separating gene pools by preventing interbreeding / gene flow within one population, eg. ○ Gamete incompatibility ○ Different breeding seasons (eg. different flowering times) ○ Different courtship behaviour preventing mating ○ Body shape / size changes preventing mating Different selection pressures act on each population So different advantageous alleles are selected for / passed on in each population So allele frequencies within each gene pool change over many generations Eventually different populations cannot interbreed to produce fertile offspring

Question 31

What is a community

Answer 31

All the populations of different species living in the same place at the same time

Question 32

What is an ecosystem

Answer 32

A community and non living components of the environment

Question 33

What is a niche

Answer 33

● The specific role of a species within its habitat, eg. what it eats, where and when it feeds ● Governed by its adaptation to both abiotic (non-living) and biotic (living) conditions

Question 34

Explain the advantage of species occupying different niches

Answer 34

Less competition for food / resources ● If two species tried to occupy the same niche, one would outcompete the other

Question 35

What is maximum carrying capacity

Answer 35

The maximum stable population size of a species that an ecosystem could support

Question 36

Interactions between an organism

Answer 36

Interspecific competition- between organisms of different species Intraspecific competition- between organisms of the same species Predation (predators kill and eat other animals, called prey)

Question 37

Explain how abiotic factors may affect population size / carrying capacity

Answer 37

If conditions favourable, organisms more likely to survive & reproduce → increasing carrying capacity ● Eg. increasing light intensity increases rate of photosynthesis, increasing nitrates increases protein production and increasing phosphates increases phospholipid production in plants ○ This increases carrying capacity of a variety of plant species ○ So increases the number and variety of habitats, niches and food sources for animals ○ So increasing carrying capacity of a variety of animal species

Question 38

Explain how interspecific competition may affect population size

Answer 38

Reduces [named resource] available to both species, limiting their chances of survival & reproduction ○ So reduces population size of both species ● If one species is better adapted, it will outcompete the other ○ So population size of less well adapted species declines, potentially leading to extinction

Question 39

Explain how intraspecific competition may affect population size

Answer 39

2. As population size increases, resource availability per organism decreases, so competition increases ○ So chances of survival & reproduction decrease → population size decreases As population size decreases, resource availability per organism increases, so competition decreases ○ So chances of survival & reproduction increase → population size increases

Question 40

Explain the changes which occur in populations of predators & prey

Answer 40

2. 3. 4. Prey population increases so predators have more food ○ So more predators survive & reproduce Predator population increases so more prey killed & eaten ○ So less prey survive & reproduce Prey population decreases so predators have less food ○ So less predators survive & reproduce Predator population decreases so less prey killed & eaten ○ So more prey survive & reproduce (cycle repeats)

Question 41

Describe how the size of a population of slow-moving or non-motile organisms can be estimated

Answer 41

Divide area into a grid / squares eg. place 2 tape measures at right angles Generate a pair of coordinates using a random number generator (eg. on a calculator) Place a quadrat here and count number / frequency of [named species] Repeat a large number of times (10 or more) and calculate a mean per quadrat Population size = (total area of habitat / quadrat area) x mean per quadrat

Question 42

Describe how the mark-release-recapture method can be used to estimate the size of a population of motile organisms

Answer 42

Capture sample of species, mark and release ● Ensure marking is not harmful / does not affect survival ● Allow time for organisms to randomly distribute before collecting second sample ● Population = (number in sample 1 x number in sample 2) / number marked in sample 2

Question 43

What assumptions does the mark-release-recapture method make?

Answer 43

2. 3. 4. Sufficient time for marked individuals to mix / distribute evenly within the population Marking not removed so marked organisms are recaptured OR marking is not toxic so doesn’t affect chances of survival OR marking not visible (to predators) so doesn 't affect predation Limited / no immigration / emigration No / few births / deaths / breeding / change in population size (or birth & death rate are equal)

Question 44

Suggest why the mark-release-recapture method can produce unreliable results in very large areas

Answer 44

● Unlikely that organisms will distribute randomly / evenly ● Less chance of recapturing organisms (that were marked initially)

Question 45

Describe and explain how primary succession occurs

Answer 45

1. 2. 3. 4. 5. Colonisation by pioneer species (first to colonise) Pioneer species (and other species at each stage in succession) change abiotic conditions ○ Eg. they die and decompose, forming soil which retains water (humus / organic matter) So environment becomes less hostile / more suitable for other species with different adaptations AND less suitable for previous species, so better adapted species outcompete previous species As succession goes on, biodiversity increases Climax community reached - final stable community (no further succession)

Question 46

Describe features of a climax community

Answer 46

● Same species present / stable community over a long time ● Abiotic factors (fairly) constant over time ● Populations (fairly) stable (around carrying capacity)

Question 47

Explain how conservation of habitats involves management of succession

Answer 47

● Further succession can be prevented to stop a climax community forming ○ By removing or preventing growth of species associated with later stages eg. by allowing grazing ● This preserves an ecosystem at a certain point / in its current stage of succession (plagioclimax) ● So early species are not outcompeted by later species and habitats / niches are not lost

Question 48

Describe the conflict between human needs and conservation as well as the importance of managing this

Answer 48

Human demand for natural resources (eg. timber) is leading to habitat destruction / biodiversity loss ● Conservation is needed to protect habitats / niches / species / biodiversity ● Management of this conflict maintains the sustainability of natural resources ○ Meeting current needs without compromising the ability of future generations to meet theirs