Topic 7 Flashcards
Monohybrid inheritance
> parents diploid
100% heterozygous for F1
F2 = 3:1
Dihybrid inheritance
> F1 generation = 100% heterozygous
> F2 generation phenotypic ration = 9:3:3:1
Codominance and multiple alleles
Example - ABO blood group, A and B are codminant and o is recessive
Epistasis
> 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)
Autosomal linkage
> 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
Autosomal linkage and crossing over
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
Haemophilia
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
Normal phenotypic ratios
Monohybrid crosses - 3:1
Dihybrid crosses - 9:3:3:1
Codominant crosses - 1:2:1
Epistatic phenotypic ratios
Recessive epistatic - 9:3:4
Dominant epistatic - 12:3:1
Sex linkage phenotypic ratio
Heterozygous dominant = 3:1
Heterozygous recessive = 1:1
The hardy weinburg principle
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
Hardy-Weinberg equation
P+Q=1
P^2 + 2pq + q^2 = 1
P = dominant
Q = recessive
Causes of variation
> most variation is a result of both
Genetic - mutation, crossing over, independent assortment, random fertilisation, inherited
Environmental causes - changes the phenotype
Speciation
> 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
Genetic drift
> affects small populations much more than large population
changes the allele frequency , is a cause of evolution
is does not depend on the environment
Directional selection
> caused by a change in environmental conditions
only those with the desired allele will survive and reproduce
mean changes
Stabilising selection
> in a stable environment
both extremes of the phenotype are less likely to survive and reproduce
the mean remains the same
Disruptive selection
> 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
Abundance of organisms
> 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
Distribution of orgnaisms
Interspecific competition and predation will affect an organisms distribution
Organisms will only exist where they can survive
Transects
> 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
Quadrats
> 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
Sampling a population
> 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
Mark-release-recapture
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
Mark-release-recapture equation
Total pop = total caught in 1st sample x total caught in 2nd sample / no marked in 2nd sample
Succession
> 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
What happens when succession takes place
> soil depth increase > H2O + nutrient availability increases > biodiversity increase > plant height increases > niches increase > light intensity on the ground decreases
Primary succession
Starts from newly formed land
Harsh biotic conditions
Very slow
Secondary succession
Starts from land where vegetation have been cleared
Less harsh abiotic conditions
Much faster
Pioneer species can be larger
Deflected succession
Stops succession - tall plants cant grow because tips are continuously cut off
Cannot outcompete low growing grasses
Grassland becomes the climax community
Climax community
Different ecosystems have different abiotic conditions - they develop into different climax communities
Chi-squared
Sum of (O-E)^2/ E
> sample over 20
> find difference between observed and expected
How is sex determined genetically
Sex is determined by the absence or presence of a y chromosome
What do species compete for
Animals - food, water, space
Plants - light, water, minerals, root space
How does predator - prey relationship affect the population size
> 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
Factors to consider when using a quadrat
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)
Measuring abundance of different species
Non moving - using a quadrat
Moving - mark-release-recapture
Managing succession to help conserve habitats
Conservation can prevent succession in order to preserve the current ecosystem
Preventing succession keeps ecosystems intact
> eg animal grazing, managed fires
Methods of conservation
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
Role of overproduction of offspring in natural selection
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
Effects of selection on evolution
Stabilising - mean survives
Directional - one extreme survives
Disruptive - both extremes survive
They dictate who will survive through evolution
Selection affecting allelic frequency
Decreases the allele frequency - only a small and specific type of allele will survive
Variation in natural selection
Allows for there to be an increase and decrease of frequency of alleles in the population
How are new species formed
Through speciation - allopatric and sympatric speciation
How do populations become geographically isolated
Movement of land masses, continental drift, mountain lines, etc
