Topic 7

Question 1

Monohybrid inheritance

Answer 1

> parents diploid
100% heterozygous for F1
F2 = 3:1

Question 2

Dihybrid inheritance

Answer 2

> F1 generation = 100% heterozygous

> F2 generation phenotypic ration = 9:3:3:1

Question 3

Codominance and multiple alleles

Answer 3

Example - ABO blood group, A and B are codminant and o is recessive

Question 4

Epistasis

Answer 4

> when a phenotype is controlled by more than one gene - one gene can either mask or suppress the expression of another gene
recessive epistatic allele - 9:3:4 (recessive prevents the expression of another allele)
dominant epistatic allele - 12:3:1 (one gene completely masks the alleles)

Question 5

Autosomal linkage

Answer 5

> genes on the same autosome are linked
they will stay together during independent assortment and will be inherited together
because linked genes are inherited together they behave like a monohybrid cross
means that more offspring will have the same phenotype and genotype as their parents

Question 6

Autosomal linkage and crossing over

Answer 6

If crossing over occurs then the alleles are separated and there will be differing genotypes and phenotypes to the parents
> closer loci is to autosome - more closely linked

Question 7

Haemophilia

Answer 7

blood los slowly and there may be slow and persistent internal bleeding
> females have two x chromosomes and you must be homozygous recessive to suffer
Males only have one x so only need one to suffer

Question 8

Normal phenotypic ratios

Answer 8

Monohybrid crosses - 3:1
Dihybrid crosses - 9:3:3:1
Codominant crosses - 1:2:1

Question 9

Epistatic phenotypic ratios

Answer 9

Recessive epistatic - 9:3:4

Dominant epistatic - 12:3:1

Question 10

Sex linkage phenotypic ratio

Answer 10

Heterozygous dominant = 3:1

Heterozygous recessive = 1:1

Question 11

The hardy weinburg principle

Answer 11

Predicts - the frequency of alleles of a gene will stay constant over generations
Assumptions - no mutations, no selection, random mating, large population, genetically isolated, no migration

Question 12

Hardy-Weinberg equation

Answer 12

P+Q=1
P^2 + 2pq + q^2 = 1
P = dominant
Q = recessive

Question 13

Causes of variation

Answer 13

> most variation is a result of both
Genetic - mutation, crossing over, independent assortment, random fertilisation, inherited
Environmental causes - changes the phenotype

Question 14

Speciation

Answer 14

> variation exists in the population due to mutation
Different selection pressures cause directional selection of differnt phenotype
differental reproductive sucess causes a change in allele frequency over many generations

Question 15

Genetic drift

Answer 15

> affects small populations much more than large population
changes the allele frequency , is a cause of evolution
is does not depend on the environment

Question 16

Directional selection

Answer 16

> caused by a change in environmental conditions
only those with the desired allele will survive and reproduce
mean changes

Question 17

Stabilising selection

Answer 17

> in a stable environment
both extremes of the phenotype are less likely to survive and reproduce
the mean remains the same

Question 18

Disruptive selection

Answer 18

> both extremes of the phenotype are more likely to survive and reproduce than the means phenotype
environment select for two separate phenotypes
contributes to sympatric speciation

Question 19

Abundance of organisms

Answer 19

> Intraspecific competition - species occupy the same niche and compete for everything
Interspecific competition - the abundance of one species will affect the other, species with a similar niche will compete for resources
abiotic factors - species can tolerate a range of conditions, where condition are optimal pop size is biggest

Question 20

Distribution of orgnaisms

Answer 20

Interspecific competition and predation will affect an organisms distribution
Organisms will only exist where they can survive

Question 21

Transects

Answer 21

> systematic sampling
record the distribution of species along the line
line transect - run a tape measure and record all that touches tape
belt transect - use quadrats along the length of transects
inherited transect - use quadrats at fixed intervals

Question 22

Quadrats

Answer 22

> random sampling
record the number of individuals in the quadrat
species frequency - how often a species is found in each square
percentage cover - if over 50% covered

Question 23

Sampling a population

Answer 23

> Random: avoids bias, divide into grid and use random generator to pick coordinates
non-ransom: systematic - samples are taken at fixed intervals
Data needs to be representative, large = more reliable, enough to carry out a stats test

Question 24

Mark-release-recapture

Answer 24

Used to estimate the abundance of a mobile species

1) capture organism
2) mark them in a way that doesn’t harm them
3) wait
4) take a 2nd sample
5) use equation

Question 25

Mark-release-recapture equation

Answer 25

Total pop = total caught in 1st sample x total caught in 2nd sample / no marked in 2nd sample

Question 26

Succession

Answer 26

> area is colonised by pioneer species - change the environmental conditions to make less hostile > allows other species to outcompete the preceding species > continues until climax community is reached

Question 27

What happens when succession takes place

Answer 27

``` > soil depth increase > H2O + nutrient availability increases > biodiversity increase > plant height increases > niches increase > light intensity on the ground decreases ```

Question 28

Primary succession

Answer 28

Starts from newly formed land Harsh biotic conditions Very slow

Question 29

Secondary succession

Answer 29

Starts from land where vegetation have been cleared Less harsh abiotic conditions Much faster Pioneer species can be larger

Question 30

Deflected succession

Answer 30

Stops succession - tall plants cant grow because tips are continuously cut off Cannot outcompete low growing grasses Grassland becomes the climax community

Question 31

Climax community

Answer 31

Different ecosystems have different abiotic conditions - they develop into different climax communities

Question 32

Chi-squared

Answer 32

Sum of (O-E)^2/ E > sample over 20 > find difference between observed and expected

Question 33

How is sex determined genetically

Answer 33

Sex is determined by the absence or presence of a y chromosome

Question 34

What do species compete for

Answer 34

Animals - food, water, space | Plants - light, water, minerals, root space

Question 35

How does predator - prey relationship affect the population size

Answer 35

> An increase in prey means more food for the predators so the predator population increases > more predators means less prey > less prey means less food for the predators so predator population decreases > less predation occurs so the prey population increases

Question 36

Factors to consider when using a quadrat

Answer 36

Size of the quadrat The number of sample quadrats to record within the study area The position of each quadrat within the study area (What will be counted in the quadrat - eg partially in/ fully in)

Question 37

Measuring abundance of different species

Answer 37

Non moving - using a quadrat | Moving - mark-release-recapture

Question 38

Managing succession to help conserve habitats

Answer 38

Conservation can prevent succession in order to preserve the current ecosystem Preventing succession keeps ecosystems intact > eg animal grazing, managed fires

Question 39

Methods of conservation

Answer 39

Plants - using seedbanks which are stores of lots of seeds Fishing quotas - limits the amount of certain fish species that fishermen can catch National parks - protect habitats Endangered species - breed in captivity

Question 40

Role of overproduction of offspring in natural selection

Answer 40

Most juveniles will not make it to adulthood Means that those with desired characteristics survive The parents genes have a higher chance of being passed on

Question 41

Effects of selection on evolution

Answer 41

Stabilising - mean survives Directional - one extreme survives Disruptive - both extremes survive They dictate who will survive through evolution

Question 42

Selection affecting allelic frequency

Answer 42

Decreases the allele frequency - only a small and specific type of allele will survive

Question 43

Variation in natural selection

Answer 43

Allows for there to be an increase and decrease of frequency of alleles in the population

Question 44

How are new species formed

Answer 44

Through speciation - allopatric and sympatric speciation

Question 45

How do populations become geographically isolated

Answer 45

Movement of land masses, continental drift, mountain lines, etc