Genetics, populations, evolution & ecosystem (3.7, chpt 17-19) Flashcards
Genotype
The genetic constitution of an organisms (the alleles it has for a gene)
Phenotype
The expression of the genes and its interaction with the environment
Homozygous
A pair of homologous chromosomes carrying the same alleles for a single gene
Heterozygous
A pair of homologous chromosomes carrying two different alleles for a single gene
Recessive allele
An allele only expressed if no dominant allele is present
Dominant allele
An allele that will always be expressed in the phenotype
Codominant
Both alleles are equally dominant and expressed in the phenotype
Multiple Alleles
More than two alleles for a single gene e.g. alleles for blood type
Sex-linkage
A gene who locus in on the X chromosome
Autosomal linkage
Genes that are located on the same chromosomes (not the sex-chromosomes)
Epistasis
When one gene modifies/masks the expression of a different gene at a different locus
Monohybrid
Genetic inheritance cross of a characteristics determined by one gene
Dihybrid
Genetic inheritance cross for a characteristic determined by two genes
How many alleles per gene do diploid organisms carry?
Two
Draw a Punnett square to show a monohybrid cross with parental genotypes of GG and gg
(pmt inheritance flashcards no.21)
Draw a Punnet square to show a monohybrid cross with parental genotypes of Gg and Gg
(inheritance flashcards pmt no.25)
Draw an example of a genetic diagram e.g. eye colour
PMT inheritance flashcards no.29
why do X and Y not form a bivalent (i.e. pair of homologous chromosomes)
as X and Y are different sizes so chromosomes are unable to line up, only short pairing regions
Give an examples of a characteristic that involves multiple alleles
Blood groups - IA, IB and IO
Why are actual ratios not exactly the same as theoretical ratios in genetics?
Because fertilisation of gametes occurs by chance - each time a gamete is fertilised, it is an independent event of what has gone before it.
Draw a Punnett square to show a dihybrid cross with parental genotypes of RrGg and RrGg
(inheritance flashcards pmt no.33)
Why are males more likely to express a recessive sex-linked allele?
- most sex-linked alleles located on x chromosome
- so males only get 1 copy of allele (so it’ll be expressed even if characteristic is recessive)
- since females get two alleles, this is less likely
Which parent do males inherit sex-linked characteristics from?
- their mother since the Y chromosome can only come from father
- so if mother is heterozygous for sex-linked alleles, she is a carrier and may pass on trait
Draw a Punnett square to show a sex-linked cross with parental genotypes of XHXh and XHY
inheritance pmt flashcards no.43
Define the two types of epistasis
recessive epistasis = where 2 homozygous recessive alleles mask expression of another allele
dominant epistasis = where 1 dominant allele masks expression of multiple other alleles
Draw a punnet square to show an epistasis cross with parental genotypes of AABB and aabb
pmt inheritance flashcards no.57
what is the chi-sqaured test?
- a stats tests to find out whether difference between observed and expected data is due to chance or a real effect
what are the criteria for the chi-sqaured test?
- data placed in discrete categories (as opposed to continuous data)
- large sample size
- only raw count data i.e. no percentages
- no data values equal zero
How is chi-squared test peformed?
- formula results in number
- number comapred to critical value (for corresponding degrees of freedom)
- if number greater than or equal to critical value we can conclude there’s a significant difference between observed and expected data and so results didn’t occur due to chance (in this case REJECT the null hypothesis)
Suppose you obtained a chi squared value of 5 and the critical value was 5.99 (2dof) - what can you conclude?
Because the chi squared value is SMALLER than the critical value - you accept the null hypothesis and there is greater than a 5% probability that the difference in the results are due to chance. There is no significant difference.
Suppose you obtained a chi squared value of 8 and the critical value was 5.99 (2dof) - what can you conclude?
Because the chi squared value is LARGER than the critical value - you reject the null hypothesis and there is less than a 5% probability that the difference in the results are due to chance. There is a significant difference.
how do you know which ‘degree of freedom’ to use in chi-sqaured?
number of categories - 1
chi-squared formula
x2= sum of: (O-E)2/ E
O= observed frequency E= expected frequency
what does more than two phenotypes indicate?
- codominance and/or multiple allele inheritnace
what six pieces of information must be shown in genetic crosses?
- parental phenotype
- parental genotype
- possible gametes
- offspring genotype
- offspring phenotype
- proportion of each phenotype (i.e. ratio)
when homozygous dominant is crossed with homozygous recessive what will be the genotype of the offspring?
- all heterozygous
unless there is autosomal linkage or crossing over in meiosis
In a dihybrid cross, if two heterozygous parents for both genes are crossed what will be the ratio you always get?
9:3:3:1
what is the impact of crossing over?
- new combinations of alleles in gametes
- therefore different proportions in punnet square
- however crossing over is rare
what is the impact of autosomal linkage?
- means alleles for each gene linked on the sane chromosome will be inherited together
- impacts the predicted gametes
what is the ratio of possible alleles of offspring when two heterozygous parents are genetically crossed with autosomal linkage?
3:1
when is it only possible to get all the phenotypes in autosomal linkage? and why would there only be few of these phenotypes?
- if crossing over occurred in meiosis to make new combinations of gametes
- crossing over is rare, so not many of these gametes formed by it will be made, therefore few of their genotypes formed and so few of the phenotypes expressed
if you don’t observe the ratio you expect in genetic crosses (e.g. monohybrid) why is that?
- crossing over has occurred
state types of inheritance
codominance multiple alleles sex-linkage autosomal linkage epistasis
Humans are diploid organisms. What does this mean? What about alleles does this explain?
We carry two copies of each chromosome - one from each parents.
What is the likely phenotypic ratio with a monohybrid cross of two heterozygous parents?
3 : 1
What things mean that you may not get the predicted phenotypic ratio?
codominant alleles and sex linkage
What would be the expected phenotypic ratio of a monohybrid cross between two heterozygous parents involving co-dominant alleles?
1 : 2 : 1
Give two reasons why the phenotypic ratio is not always the actual one.
Linkage or epistasis
What is a ‘carrier’ in terms of alleles
A person carrying an allele which is not expressed, but can be passed on to offspring
Why can’t males be the carriers of X-linked disorders?
they only have one X chromosome so if they have the disorder it will be expressed.
Why are genes on the same autosome said to be linked?
They stay together during independent segregation in meiosis 1, and their alleles will be passed on to offspring together
Why might the genes on the same autosome NOT be passed on together?
If cross over splits them up first
What is the relationship between the distance genes are from each other on the autosome and how closely they are said to be linked?
The closer they are on the autosome, the more closely they are said to be linked - crossing over is less likely to split them up
You are given the ratio 126 : 81 : 148 : 133. How would you simplify this ratio?
divide them all by the number on the far right to get a : b : c : 1
If the recessive allele is epistatic, how would it it mask the expression of the other gene’s allele?
You would need two copies of it
What is a null hypothesis?
It is that there is no significant different between the observed and expected results.
species exist as what?
one or more populations
Define Population
Group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Define Gene pool
all the alleles of all the genes within a population at one time
Define Allele frequency
the proportion of an allele within the gene pool
What is the Hardy-Weinberg principle?
a mathematical model which can be used to predict the allele frequencies within a population
( as well as if allele frequency is changing over time.)
What assumptions does the Hardy-Weingburg principle make?
- these assumptions impedes the accuracy
assumptions:
- No migration/ population is isolated (to prevent introducing/removing alleles to population)
- No mutations (to create new alleles)
- No selection (favouring particular alleles)
- Mating is random (no inbreeding)
- Population is Large
state what the Hardy-Weinberg principle predicts
- proportion of dominant and recessive alleles of any genes in the population remains the same from one generation to the next
Explain the Hardy-Weinberg equation for calculating allele frequency
- frequencies of each allele for a
characteristic must add up to 1.0. - equation is therefore; p + q = 1
Where p= frequency of the dominant allele, and q= frequency of the recessive allele
Explain the Hardy-Weinberg equation for
calculating genotype frequency
- frequencies of each genotype for a
characteristics must add up to 1.0 - equation is therefore; p2+ 2pq + q2 = 1
- Where p2= frequency of homozygous dominant, 2pq= frequency of heterozygous, and q2= frequency of homozygous recessive.
Give genetic factors that cause
phenotypic variation within a species
- Mutation of alleles.
- Random fertilisation by gametes.
- Random/independent assortment/segregation of genetic material during meiosis
What is the primary source of genetic variation?
mutation
Other than genetic factors, why else may phenotype vary within a species?
environmental influences
Why does natural selection occur?
- Predation
- Disease
- Competition
they create SELECTION PRESSURES
All resulting in differential survival and
reproduction
How does natural selection cause a change in a population’s gene pool over generations?
- Organisms with advantageous
characteristics are more likely to survive, reproduce and pass their favourable alleles to offspring. Frequency of unfavourable alleles decreases and frequency of favourable alleles increases over time - this is different(ial) reproductive success, as not all individuals likely to reproduce and this results in changes in allele frequencies within a gene pool
define natural selection
process by which frequency of beneficial alleles gradually increases in population’s gene pool over time
define evolution
the gradual change in allele frequency within population over time due to natural selection
state three types of selection
stabilising
directional
disruptive
what is stabilising selection?
- occurs when environmental conditions stay the same
- individual with phenotype closest to mean are favoured, and extreme traits/phenotypes are selected against
- results in low diversity
e. g. baby birth weights
what is directional selection?
- occurs when environmental conditions change
- individuals with phenotype suited for new conditions will be more likely to survive and reproduce, passing on their alleles (ONE extreme phenotypes selected for)
- over time the mean of the population will move towards these characteristics
what is disruptive selection?
- opposite of stabilising selection, in that both extremes of normal distribution are favoured over the mean
- over time, the population becomes phenotypically divided
which type of selection is the most important in bringing about evolutionary change?
- disruptive
- however, it’s the least common form of selection
continued disruptive selection can lead to what?
speciation = with two or more or different species forming and those with mean/intermediate phenotype being selected against and (reproduce less) becoming extinct
What is speciation?
- evolution of new species from existing ones
- where population is split and (reproductively) isolated, there are different selection pressures on the two groups
- if differences in gene pools accumulate past a certain extent, the 2 groups can’t interbreed to produce fertile offspring as they’ve become separate species
what are the two types of speciation?
allopatric (geographical) and sympatric (change in reproductive mechanisms) speciation
what is meant by allopatric speciation?
- populations separated geographically leading to reproductive isolation e.g. river, mountain range
- the environments occupied by the two groups are different (i.e. different selection pressure) so different alleles are selected for and against in both environments, overtime allele frequency in gene pool changes in both environments leading to great genetic differences, forming 2 different species
describe the process by which allopatric speciations takes place [~ 5 MARKS]
[1] geographical isolation
[2] separate gene pools/no interbreeding
[3] variation due to random (beneficial) mutations
[4] different selection pressures
[5] different(ial) reproductive success i.e. those with alleles selected for are more likely to survive and reproduce, passing on alleles
[6] leads to change in allele frequency in separated groups - genetic differences increasing forming 2 new species (i.e. can no longer interbreed to produce fertile offspring)
what is meant by sympatric speciation?
- speciation resulting from non-physical barrier e.g. a mutation that impacts reproductive behaviour
- like any changes in anatomy (penis can’t enter vagina) or behaviour (differences in courtship ritual or be fertile at different times of the year) could also prevent breeding (and producing fertile offspring)
- overtime reproductively isolated populations will accumulate different mutations so DNA is so different they can’t interbreed to create fertile offspring - classed as 2 different species
Define genetic drift
- change in a population’s allele frequency between generations (occurs due to chance rather selection pressures)
- continual substantial genetic drift results in evolution
Why does genetic drift affect small populations more than large ones?
- gene pool is smaller, so there are less alleles available and any changes in frequency become pronounced/significant very quickly
natural selection and isolation results can result in what?
change in allele and phenotype frequency and lead to formation of a new species
Define a community
All the populations of different species in the same area at the same time
Define a habitat
Part of an ecosystem in which particular organisms live
Define an ecosystem
A community and the non-living components of an environment (and abiotic factors)
- ecosystems can range in size from very small to the very large
Define a niche
an organism’s role within an ecosystem, including their position in the food web and habitat
note: each species occupies their own niche governed by adaptation to both abiotic and biotic conditions
Define the carrying capacity
the maximum population size an ecosystem can support
Define abiotic factors, give examples
non-living conditions of an ecosystem e.g. light. temperature
Define biotic factors, give examples
living features of an ecosystem
e.g. predators, disease
Name four abiotic factors that affect population growth
- Temperature
- Light
- pH
- Water/humidity
What is meant by intraspecific and interspecific competition?
Intraspecific = competition between
organisms of the same species e.g. courtship ritual
Interspecific = competition between
organisms of different species e.g. for same resources in a limited supply like habitat, food (sources) and water
What resources might organisms compete for?
Food, water, shelter, minerals, light,
mates (intraspecific only).
Describe the pattern of a typical
predator-prey relationship in terms of
population change
● Prey is eaten by predator, resulting in predator population increasing and prey population decreasing.
● Fewer prey means increased competition for food, so predator population decreases.
● Fewer predators means more prey survives, and the cycle begins again.
describe how abiotic factors can affect the size of different populations
- plants and animals are adapted to abiotic factors with their ecosystem
- adaptations develop through process of natural selection over many generations
- the less harsh the abiotic factors e.g. plenty of water and light, the larger the range of species and the larger the population sizes
population size can vary as a result of:
- the effect of abiotic factors
- interactions between organisms: interspecific and intraspecific competition and predation
regardless of species what three features will a predator-prey graph display
- the size of the predator and prey population both fluctuate
- prey population will always peak at a higher point (than predators)
- the size of the population will always change in the prey and then the predators (lag time)
How can you estimate the size of a population?
- quadrats (randomly placed and belt transects)
- mark-release-recapture method (for motile organisms)
how can it be ensured samples accurately represent population?
- random sampling in uniform areas to eliminate bias
- line transects to examine a change over distance
- large number of samples (30+)
which sampling technique should be used for estimating population of slow-moving or non-motile organisms?
sample using a quadrat
uniform distribution: random sampling
uneven distribution: belt transect
which sampling technique should be used for estimating population of motile organisms?
mark-release-recapture method
describe the process of using a belt transect
- stretching string or tape across ground in straight line
- a frame quadrat is laid down along line and species within it recorded
- moved alongside length in intervals and process repeated
- gives record of species in a continuous belt
describe the random sampling method
- lie two tape measures at a right angle to create a gridded area
- use a random number generator to generate two coordinates
- place the quadrat and collect the data (density/percentage cover/frequency)
- repeat at least 30 times and calculate a mean
difference between belt transect and interrupted belt transect
belt transect = quadrat is placed at every position along the tape measure
interrupted belt transect = quadrat is placed at uniform intervals along the tape measure e.g. every 5 metres
describe the line transect method (e.g. beach)
- place the tape measure at a right angle to the shore line
- place the quadrat every 5 metres/every position
- collect the data (density/percentage cover/local frequency)
- repeat by placing another 30 transects along the beach at right angles to the shore line (i.e. do the whole thing again 30 times)
methods to estimate the abundance of a species whilst sampling
1 local frequency (% of sqaures in quadrat with species present)
2 density (the number of one species in a given area)
3 percentage cover (proportion of the ground occupied by the species, square must be at least half covered to be counted)
Why would you use samples?
too time-consuming to measure the number of individuals in a species
evaluate using local frequency as a method to estimate the abundance of a species
(+ve)
- quick method to sample large area
- useful if too difficult to identify individual organism (e.g. moss) or too many to count (e.g. grass)
(-ve)
- poor accuracy as doesn’t;t consider overlapping plants or the size of the plant
evaluate using density as a method to estimate the abundance of a species
(+ve)
- more accurate if you can easily distinguish an individual plant (and there aren’t too many to count e.g. daises)
- can be used to estimate species richness (count number of different species present)
(-ve)
- more time consuming
evaluate using percentage cover as a method to estimate the abundance of a species
(+ve)
- quicker method than density
- useful if too difficult to identify individual organisms (e.g. moss) or if too many to count (e.g. grass)
(-ve)
- subjective so limits accuracy
- doesn’t consider overlapping plants or the size of the plant
mark-release-recapture method is used
in sample to estimate population size of what type of organisms?
motile organisms
Describe the mark-release-recapture method
- capture sample and count them
- mark them harmlessly (e.g. doesn’t increase chances of being seen by predator, doesn’t decrease chances of reproduction), mark should be weather-resistant
- release them back into their habitat
- wait appropriate time for them to randomly distribute within population (e.g. a week) and take a second sample from the same population
- count how many of the second sample are marked
- estimate total pop size by:
total population size = (number caught in 1st sample*number caught in 2nd sample)/number marked in 2nd sample
What are the assumptions made in the mark-release-capture method?
● Marked individuals distribute evenly (in reality they may all huddle near food)
● No migration in or out of the population (i.e population size constant)
● No/Few births or deaths (i.e. population size constant)
● Method of marking does not affect survival (e.g. more easily seen by predator)
● Mark does not come off.
- more times this is repeated the more reliable the results
ethics of mark-release-recapture
mark must cause no permanent harm
considerations for the mark:
- non-toxic
- must not increase chances of predation
- must not reduce chances of reproduction
Why are ecosystems described as being dynamic?
● Populations constantly rise and fall. ● Any small change can have a large effect. ● Biotic and abiotic factors may alter the conditions of the ecosystem.
What is meant by primary succession?
- where an area previously devoid of life
is colonised by a community of
organisms (i.e. pioneer species) - there is NO soil to begin with, occurs on newly exposed surfaces e.g. new volcanic rocks
Succession process (5)
- Pioneer species colonises (as it can survive harsh conditions)
- Makes abiotic conditions less hostile
- New species outcompetes pioneer species because better competitor (I.e better adapted)
- New species increase in number, pioneer species decrease in number.
- Climax community established
= the organisms that make up the final stage of ecological succession
- normally has one dominant plant species, one dominant animal species
How does pioneer species make abiotic conditions less hostile?
their decomposition adds nutrients to ground
define pioneer species
A species that can colonise bare rock or ground
- i.e. the first organism to colonise in primary succession
Give 5 common features of pioneer species.
- Many wind-dispersed seeds/spores - reach isolated areas
- Rapid seed germination - no dormant period required
- Photosynthesising - for food
- Nitrogen-fixing - for nutrients
- Xerophytes
What is the climax community and how is it reached?
- final stage of succession, where the ecosystem is balanced and stable. - reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing
How might a species alter the environment that develops during succession?
- species may improve the environment to make it more suitable for other species.
- alternatively, a species may worsen
environment by making it less suitable for other species
5 features following succession?
Abiotic conditions less hostile/more habitats/more niches Increased biodiversity More complex food webs Increased biomass Increased stability
describe what is meant by secondary succession
- series of community changes which take place on a previously colonized, but disturbed or damaged habitat (e.g. by forest fires)
- soil layer already present, succession begins at later stage
what is conservation?
- The protection and management of
species and habitats, to maintain biodiversity (i.e protection and management of ecosystems)
what is plagioclimax?
stage in succession where artificial or natural factors prevent the natural climax community from forming
what’s humus?
- organic material that is comprised of the dead pioneer species that is decomposed by microorganisms
What is dominant species (in succession)?
- the better adapted plants or animals to the improved conditions
Why might conservation involve managing succession?
- succession could lead to a climax community with a different dominant species
↪ loss of habitat
Conservation techniques (in managing succession)
seed banks
↪ if plant become extinct, stored seeds can be planted
- fishing quotas
↪ limits amount of fish species fishermen can catch
↪ help conserve fish species by reducing numbers caught and killed - protected areas
↪ eg nature reserves to restrict urban development - breeding in captivity
↪ endangered species can increase in numbers then return to the wild
How to evaluate evidence and data about conservation issues?
- Describe data
↪ use figures - Draw conclusions
- Evaluate method
↪ control variables
↪ sample size
↪ bias
EXAM QUESTION
Farmland previously used for growing crops was left for 30 years and developed into
woodland. During this period, ecologists recorded an increase in the diversity of
birds in the area.
Name the process that resulted in the development of woodland from farmland. (1)
Explain the increase in the diversity of birds as the woodland developed.(3)
Succession;
- Greater variety/diversity of plants/insects / more
plant/insect species; - More food sources / more varieties of food;
- Greater variety/more habitats/niches;
REQUIRED PRAC 12: List 3 abiotic factors.
Light intensity Humidity
Temperature Wind speed
Water supply Day length
Nutrient supply Rainfall
REQUIRED PRAC 12: List 3 biotic factors
Competition for resources
Predation
Disease
REQUIRED PRAC 12: How is percentage cover calculated?
- Use a quadrat with squares. Count how many squares the required species is present in.
- Only count a square if more than half of the square is covered. Calculate the percentage of squares the species is present in
Outline the procedure to REQUIRED PRAC 12: Investigation into the effect of a named environmental factor
on the distribution of a given species
- Choose an area to take samples from. Use a random number generator to
generate 10 sets of random coordinates. - Use two tape measures to create a set of axes off which coordinates can be
read. - Place the quadrat at each of the coordinates, placing the bottom left corner on
the coordinate every time. - Record the percentage cover for the chosen species.
- At each coordinate, a measure of the independent variable should be taken.
Eg. if investigating effect of light intensity: record light intensity using a photometer at each location
REQUIRED PRAC 12: How can the results be used to determine the relationship between the chosen factor and the percentage cover?
● Plot a graph of the percentage cover against the chosen independent variable
● Use a statistical test eg. Spearman’s rank, T-test and Chi-squared on collected data
REQUIRED PRAC 12: Why should a random number generator be used?
● To avoid bias in random sampling
REQUIRED PRAC 12: What sould you be aware of in investigating effect of named environmental factor (e.g. light intensity) on the distribution of a given species
● correlation is not necessarily causation: there could be a range of
factors that influence the results
how is soil formed in primary succession?
- pioneer species die and decompose
- decomposed by microorganisms thus adding humus
- leads to formation of soil which makes environment more suitable for more complex organisms
(over time soil becomes richer in minerals which allows larger plants e.g. shrubs to survive — eventually, climax community established)
what does the H-W principle predict?
- frequency of an allele in a gene
- stays constant over many generations
- providing there’s no mutation/selection and mating is random
suggest one reason for conserving woodlands
- Conserving / protecting habitats / niches;
- Conserving / protecting (endangered) species / maintains / increases
(bio) diversity; - Reduces global warming / greenhouse effect / climate change / remove /
take up carbon dioxide; - Source of medicines / chemicals / wood;
- Reduces erosion / eutrophication
