4B - Diversity, Classification And Variation Flashcards
What are gametes?
- Sex cells with a haploid number of chromosomes (n)
* Sperm cells in makes and egg cells in females
What is fertilisation?
When a haploid sperm and haploid egg fuse to give a zygote with a diploid number of chromosomes.
What does haploid mean?
Having only one chromosome from each pair.
What does diploid mean?
Having two of each chromosome.
What is the symbol for haploid?
n
What is the symbol for diploid?
2n
What is formed when two gametes join?
Zygote
Are gametes haploid or diploid?
Haploid (n)
Are normal body cells haploid or diploid?
Diploid (2n)
In a normal body cell, where does each of the two chromosomes in a pair come from?
One from the mother and one from the father.
How does fertilisation produce genetic diversity?
- Any sperm can fertilise any egg
* So random fertilisation can produce zygotes with different combinations of chromosomes to both parents.
How is fertilisation random?
Any sperm can fertilise any egg.
How are gametes formed?
By meiosis.
Where does meiosis take place?
In the reproductive organs.
What are chromatids?
- Identical copies of a chromosome made by semi-conservative replication.
- i.e. In a double-armed chromosome, each arm is called a chromatid.
What is a centromere?
The point where the chromatids are joined in a double-armed chromosome.
Describe the process of meiosis.
1) Before meiosis, DNA unravels and replicates so there are two copies of each chromosome, called chromatids (i.e. 2 copies of mother’s chromatid 1 and 2 copies of father’s chromatid 1)
2) DNA condense to form double-armed chromosomes made from two sister chromatids and joined by a centromere.
MEIOSIS I
3) Chromosomes arrange themselves into homologous pairs (two double-armed chromosomes make up a homologous pair)
4) Chromatids twist around and sections of the chromosomes swap over -> Have the same genes, but different alleles.
5) The homologous pairs are separated randomly, so that it is random which chromosome from each pair ends up in which daughter cell.
MEIOSIS II
6) Pairs of sister chromatids in each chromosome are separated -> Centromere is divided.
7) Four haploid cells (gametes) that are genetically different are produced.
Describe the chromosome number before meiosis.
2n
Describe the chromosome number after DNA is replicated before meiosis I.
2 x 2n
Describe the chromosome number after meiosis I.
2 x n
Describe the chromosome number after meiosis II.
n
What are autosomes?
Chromosomes other than sex ones.
What are homologous chromosomes?
- Corresponding chromosomes from a pair, one from the father and one from the mother.
- Of the same size and with the same genes.
- e.g. Chromosome 1 from your mother and chromosome 1 from your father.
Remember to practise writing and drawing out the process of meiosis.
Pg 88 of revision guide.
How does the definition of chromosome change throughout meiosis?
- When a chromosome is on its own, it is called a chromosome
- Where there is a double-armed X structure, the whole thing is called a chromosome, while each branch is called a chromatid
When asked to spot when meiosis happens in an organism, what must you do?
Remember that meiosis is needed to produce gametes with half the number of chromosomes as the parent cell
When in meiosis is chromosome number halved?
- During meiosis I.
- NOT during meiosis II, because the number of chromosomes stays the same -> They just become single-armed instead of double-armed (even though genetic material is halving).
What are the two ways in which meiosis produces genetic diversity?
1) Crossing over of chromatids in meiosis I
2) Independent segregation of chromosomes in meiosis I
Describe the crossing over of chromatids in meiosis I.
- Homologous pairs of chromosomes come together and pair up
- Chromatids twist around each other and parts of chromatids swap over
- Chromatids still contain the same genes, but now have a different combination of alleles
Describe how crossing over of chromatids in meiosis I produces genetic diversity.
Each of the four daughters cells formed from meiosis contains chromatids with different alleles.
Remember to practise drawing out the process of crossing over of chromatids in meiosis I.
Pg 89 of revision guide
What is the name for the random sorting of chromosomes into daughter cells in meiosis I?
Independent segregation
Describe independent segregation of chromosomes in meiosis I.
- Each homologous pair of chromosomes in your cells is made of one chromosome from your mum and one from you dad
- When these are separated in meiosis I, it’s random which chromosome from each pair ends up in which daughter cell
- This is called independent segregation
Describe how independent segregation of chromosomes in meiosis I produces variation.
- Each homologous pair of chromosomes in your cells is made of one chromosome from your mum and one from you dad
- When these are separated in meiosis I, it’s random which chromosome from each pair ends up in which daughter cell
- So the four daughter cells produced have completely different combinations of those maternal and paternal chromosomes.
Remember to practise drawing out the process of independent segregation in meiosis I.
Pg 89 of revision guide.
Give all of the sources of genetic variation in reproduction.
- Meiosis I -> Crossing over between chromatids
- Meiosis I -> Independent segregation
- Random fertilisation
Compare the cells produced by meiosis and mitosis.
MITOSIS
• Same number of chromosomes as the parent cell
• Generically identical to each other and parent cell
• Two daughter cells
MEIOSIS
• Half the number of chromosomes as the parent cell
• Generically different from one another and the parent cell
• Four daughter cells
Explain why meiosis and mitosis have different outcomes.
- Mitosis has one division, while meiosis has two -> Mitosis produces 2 cells with the same number of chromosomes as the parent cell, while meiosis produces 4 cells with half
- Meiosis involves crossing over of chromatids and independent segregation, while mitosis doesn’t -> Mitosis produces genetically identical cells, while meiosis produces genetic variation
What is a chromosome mutation?
- When there is an error in meiosis so that the cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes.
- e.g. Having a 3rd chromosome in a certain pair.
What causes chromosome mutation?
Errors in meiosis
Why do chromosome mutations lead to inherited conditions?
The errors are present in the gametes.
Describe what causes Down’s Syndrome.
1) Caused by a person having an extra copy of chromosome 21 (or part of it).
2) Non-disjunction occurs in meiosis I -> One cell gets an extra copy of 21 and another gets none.
3) When the gametes fuse at fertilisation, the resulting zygote will have three copies of chromosome 21.
What is the name for the failure of chromosomes to separate properly in meiosis I?
Non-disjunction
In which part of meiosis can non-disjunction occur?
Meiosis I
Down’s Syndrome is caused by having an extra chromosome…
21
Remember to practise drawing out how Down’s Syndrome can occur.
Pg 90 of revision guide.
What is a gene mutation?
A change in the base sequence of DNA.
What is the difference between chromosome mutation and gene mutation?
- Chromosome mutation -> When cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes.
- Gene mutation -> When there is a change in the DNA base sequence of chromosomes.
What are the two main types of gene mutation?
- Substitution
* Deletion
What is substitution?
- When one base is substituted with another.
* e.g. ATGCCT becomes ATTCCT
What is deletion?
- When one base is deleted, shifting the rest of the code to the left.
- e.g. ATGCCT becomes ATCCT
Aside from substitution and deletion, what are some other types of mutations?
- Insertion
- Duplication
- Addition
- Translocation
Why effect might a gene mutation have and why?
- The order of DNA bases determines the order of amino acids in a particular protein.
- If a mutation occurs, the sequence of amino acids or codes for (and the protein formed) could be altered.
Why might not all gene mutations affect the order of amino acids in the resulting polypeptide?
- Genetic code is degenerate -> Some amino acids are coded for by more than one triplet
- Some substitutions might change a triplet in such a way that the same amino acid is added to the polypeptide
Which gene mutations are likely to affect the order of amino acids?
- Substitution -> Sometimes lead to a change in the amino acid sequence
- Deletion -> Always lead to a change in the amino acid sequence, due to frame shift
What happens when deletion occurs in a gene?
- The bases to the right of the deletion will shift to the left -> Frame shift
- This means that different amino acids are added to the polypeptide
- A completely different protein is produced
When do gene mutations occur?
Spontaneously -> e.g. when DNA is misread during replication.
Compare when chromosome mutations and gene mutations are likely to happen.
- Chromosome mutations -> During meiosis
* Gene mutations -> During DNA replication
What is frame shift?
When a base is deleted and all of the bases to the right of it shift to the left.
What can increase the rate of gene mutation?
Mutagenic agents
Give some examples of mutagenic agents.
- UV radiation
- Ionising radiation
- Some chemicals
- Some viruses
What is a population?
A group of organisms of a one species living in a particular habitat.
What is genetic diversity?
The number of different alleles of genes in a species or population.
What is a gene pool?
The total number of alleles in a given population at the time.
What is allele frequency?
The number of times an allele appears in the population for a specific gene.
What is reproductive success?
How successful an individual is at breeding and producing offspring.
What things can increase genetic diversity in a population?
- Mutations in the DNA -> Forming new alleles
* Different alleles being introduced into a population by a migrating individual
What is gene flow?
When different alleles are introduced into a population by individuals that migrate into them and reproduce.
What is genetic diversity responsible for?
Natural selection
What is a genetic bottleneck?
- An event that causes a big reduction in a population
* e.g. when a large number of organisms within a population die before reproducing
What is the effect of a genetic bottleneck?
- There is a large reduction in a population.
- Reduced number of different alleles in the gene pool.
- This reduces the genetic diversity.
- The survivors reproduce and a larger population is created with less genetic diversity.
Give an example of a genetic bottleneck and its effect.
- Northern elephant seals were hunted by humans in the late 1800s.
- Original population was reduced to about 50 seals.
- Since then, these seals have produced a population of about 170,000.
- But this population has very little genetic diversity compared to southern elephant seals, who never suffered this.
What is the founder effect?
- When just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool.
- It is a type of genetic bottleneck.
What effect might the founder effect have on genetic diseases and why?
- There may be a higher incidence of certain genetic diseases.
- Because the frequency of each allele in the new colony might be different from the original population.
- An allele that was rare in the original population might be more common in the new colony.
Give an example of a type of genetic bottleneck.
The founder effect.
Why might the founder effect occur?
- Migration leading to geographical separation
* Separation of a colony for another reason, e.g. religion
Give an example of the founder effect and its effects.
- Amish population of North America are all descended from a small number of Swiss who migrated there.
- The population shows little genetic diversity.
- They have remained isolated due to their religious beliefs, so no new alleles have been introduced.
- Population has an unusually high incidence of certain genetic disorders.
Are mutations good or bad? Why?
- They can result in a new allele
- This allele can be harmful -> So it does out quickly
- This allele can be beneficial -> Natural selection helps the frequency of that allele in a population increase
How can you work out he number of possible chromosome combinations following meiosis and then fertilisation?
- After meiosis = 2^n
- After fertilisation = (2^n)²
Where n = number of pairs of homologous chromosomes.
Calculate the number of possible chromosome combination produced from the fertilisation of two gametes from separate individuals whose diploid number is 12.
- n = 12 / 2 = 6
* (2^n)² = (2^6)² = 4096
Are all individuals in a population equally likely to reproduce?
- No, there is differential reproductive success.
* Individuals with beneficial alleles are more likely to survive and reproduce.
Describe how natural selection can happen.
1) Variation in phenotype due to variation in alleles via mutation.
2) So there is a differential reproductive success.
3) There is selective pressure, such as a predator.
4) Individuals with a beneficial allele are more likely to survive, reproduce and pass on the beneficial allele.
5) So a greater proportion of the next generation inherits the beneficial gene -> This repeats.
6) The frequency of the beneficial allele increases through generations.
7) Over time, this leads to evolution.
What is evolution?
The gradual change in species over time.
What are two keys factors in evolution?
- Adaptation
* Selection
What do adaptations do?
Help organisms survive in their environment.
What are the 3 types of adaptation?
1) Behavioural adaptations
2) Physiological adaptations
3) Structural adaptations
What are behavioural adaptations?
Ways an organism acts that increase its chance of survival and reproduction.
Give an example of a behavioural adaptation.
Possums may “play dead” if they’re being threatened by a predator to escape attack.
What are physiological adaptions?
Processes inside an organism’s body that increase its chance of survival.
Give an example of a physiological adaptation.
Brown bears hibernate over winter -> Lower their rate of metabolism, which conserved energy.
What are structural adaptations?
Physical features of an organism’s body that increase its chance of survival.
What is another name for structural adaptations?
Anatomical adaptations
Give an example of a structural adaptation.
Whales have a thick layer of blubber, which helps them keep warm in the cold sea.
What are the two types of natural selection?
- Stabilising selection
* Directional selection
What is directional selection?
- Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
- This causes the mode to shift to the extreme.
Give an example of directional selection.
- Antibiotic resistance
- When bacteria are exposed to an antibiotic, the ones with the allele that gives them resistance are more likely to survive and reproduce, passing on the allele.
- The mode shifts towards high antibiotic resistance.
How does directional selection work?
- Environmental change occurs
- One extreme of the phenotype is better adapted for survival, while the mode and other extreme are acted against
- The better adapted extreme phenotypes are more likely to reproduce and pass on their alleles, as oppose to the disadvantaged extreme
- So the mode shifts to the extreme phenotype
How does directional selection affect the mode and diversity?
- Mode -> Shifts to an extreme
* Diversity -> Slightly decreases (at least initially)
What is stabilising selection?
- Where individuals with allele for characteristics towards the middle of the range are more likely to survive and reproduce.
- Mode doesn’t shift, but diversity is reduced.
Give an example of stabilising selection.
- Human birth weight
- Very light and heavy babies are unlikely to survive to be able to reproduce
- So medium-sized babies are most likely to survive and eventually reproduce, passing on their alleles
- This causes the mode weight to shift to the medium, reducing the range.
How does stabilising selection work?
- Environmental is unchanging
- Extreme phenotypes are not as well adapted for survival as the middle
- The better adapted middle phenotypes are more likely to reproduce and pass on their alleles, as oppose to the disadvantaged extreme
- So the mode shifts to the middle phenotype, reducing the extreme diversity
How does stabilising selection affect the mode and diversity?
- Mode -> Constant
* Diversity -> Decreases
Remember to practise drawing out graphs for stabilising and directional selection.
Pg 94 of revision guide.
Compare what causes directional and stabilising selection.
- Directional -> Environmental change
* Stabilising -> Unchanging environment
Describe the data at the bottom of pg 94 and suggest a possible cause.
- Over the first two years, the average fur length is about 21mm, but this gradually increases to 24mm -> Directional selection
- Rabbits with longer fur are more likely to survive the cold winters. This makes them more able to reproduce and pass on the allele for long fur.
- Over time, this allele becomes more common in the population and the average fur length increases.
Describe an experiment to test the effects of antibiotics on bacteria.
1) Use bacteria grown in a liquid broth (a mixture of distilled water, bacterial culture and nutrients).
2) Use a wire inoculation loop to transfer bacteria from the broth to an agar plate -> Spread the bacteria using the loop.
3) Place paper discs soaked with different antibiotics spaced out on the plate. Various concentrations should be used.
4) Also add a disc soaked in sterile water as a negative control.
5) Tape a lid onto the Petri dish, invert, and incubate at about 25*C for 24-48 hours.
6) This allows bacteria to grow and form a “lawn”. Anywhere the bacteria can’t grow is seen as a clear patch (inhibition zone).
7) The size of the inhibition zone around a disc shows how effective that antibiotic is.
8) NOTE: A similar technique can be used to investigate the effects of antiseptics or disinfectants.
(See diagram pg 95 of revision guide)
What is a liquid broth?
A mixture of distilled water, bacterial culture and nutrients in which bacteria can be grown.
In the experiment to investigate the effects of antibiotics on bacterial growth, what is used to transfer bacteria to the agar dish?
Wire inoculation loop
In the experiment to investigate the effects of antibiotics on bacterial growth, what is the clear zone around each disc called?
The inhibition zone.
What else can the experiment to investigate the effects of antibiotics on bacterial growth be used to test?
The effects on microbial growth of:
• Antiseptics
• Disinfectants
What are aseptic techniques?
Experimental techniques used to prevent contamination of cultures by unwanted microorganisms.
Why are aseptic techniques important?
- Contamination can affect the growth of the microorganism that you’re working with.
- Contamination with disease-causing microbes could make someone ill.
In the experiment to investigate the effects of antibiotics on bacterial growth, what are some important aseptic techniques?
- Regularly disinfect work surfaces
- Work near a Bunsen flame -> Hot air rises, so any microbes in the air should be drawn away from the culture you’re working on.
- Sterilise the wire inoculation loop before and after each use by passing it through a Bunsen flame for 5 seconds.
- Briefly flame the neck of the container of broth just after opening and just before closing -> Causes air to move out of the container, preventing unwanted organisms from falling in
- Sterilise all glassware before and after use -> e.g. in an autoclave
Why is working near a Bunsen burner flame an aseptic technique?
Hot air rises, so any microbes in the air should be drawn away from the culture you’re working on.
Why is flaming the neck of the glass container of liquid broth (just after it’s opened and just before it’s closed) an aseptic technique?
This causes air to move out of the container, preventing unwanted organisms from falling in.
What is an autoclave?
A machine which steams equipment at high pressure.
What is phylogeny?
- The study of evolutionary history of groups of organisms.
* It tells us who’s related to whom and how closely related they are.
What does a phylogenetic tree show?
- Common ancestors of species.
- How closely related species are.
(See diagram pg 96 of revision guide)
Looking at a phylogenetic tree, how can you tell how closely species are related to each other?
- Look at how recently the species diverged.
* The more recently, the more closely the species are related.
Are common ancestors still alive?
No, they are usually extinct.
What is taxonomy?
- The science of classification.
* It involves naming organisms and organising them into groups.
What is the name for the study of how organisms have evolved?
Phylogeny
What is the name for the study of grouping organisms together?
Taxonomy (or classification)
What is the difference between phylogeny and taxonomy?
- Phylogeny -> Evolutionary history of organisms
* Taxonomy -> Grouping together related organisms
How are phylogeny and taxonomy related?
Scientists now take into account phylogeny when classifying organisms -> Group them according to their evolutionary relationships
How many classification levels are there?
8
What are the 8 levels of classification called?
Taxa (singular taxon)
What is the name for the structure into which classification groups are arranged?
Hierarchy
In a classification hierarchy, where are the largest and smallest groups?
- Largest -> At the top
* Smallest -> At the bottom
Can organisms belong to more than one group in each level of the classification hierarchy?
No, there is no overlap.
Name all the levels of classification (taxa).
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
How many domains are there?
3
Name all the domains.
- Eukarya
- Bacteria
- Archaea
What are the four kingdoms in the Eukarya domain?
- Protoctista
- Fungi
- Plantae
- Animalia
Remember to revise the structure of a classification hierarchy.
See diagram pg 96 of revision guide.
Describe how the number of groups and number of organisms in each group changes as you move down the classification hierarchy.
- Number of groups -> Increases
* Number of organisms in each group -> Decreases
Define species.
- A group of similar organisms able to reproduce to give fertile offspring.
- Members are similar to each other but different to other species in their characteristics.
Can different species breed?
Some can, but only members of a single species can produce fertile offspring.
Is the classification system ever changed?
Yes, it is constantly updated because of discoveries about new species and new evidence about organisms.
What is the naming system used in classification called?
The binomial system.
Describe how the binomial system of naming organisms works.
- All organisms are given one internationally accepted scientific name in Latin that has two parts
- First part -> Genus name with a capital letter
- Second part -> Species name with a lowercase letter
- Names are always written in italics (or underlined if they’re handwritten)
In the binomial naming system, what is the first part of the name and how is it written?
- Genus name
* Capital letter
In the binomial naming system, what is the second part of the name and how is it written?
- Species name
* Lowercase letter
How are names in the binomial naming system written?
- If typed -> Italics
* If handwritten -> Underlined
Why is the binomial naming system used?
- To help avoid the confusion of common names.
* e.g. Over 100 different plant species are called raspberries.
What are the key features of the bacteria domain?
- No membrane-bound organelles
- Unicellular
- Smaller ribosomes (70S)
- Murein cell walls
- Single loop of naked DNA (no histones)
What are the key features of the eukarya domain?
- Membrane-bound organelles
- Membranes contain fatty acids attached to glycerol by ether linkages
- Not all possess cells with cell wall -> If do, then contain no murein
- Larger ribosomes (80S)
What are the key features of the archaea domain?
- Genes and protein synthesis more similar to eukaryotes
- Membranes contain fatty acids attached to glycerol by ether linkages
- No murein in cell walls
- More complex form of RNA polymerase
What is courtship behaviour?
Simple or more complex behaviours or actions carried out by organisms to attract a mate of the right species.
Why can courtship behaviour be used to classify species?
It is species specific, meaning only members of the same species will do and respond to that courtship behaviour.
What does the courtship behaviour of two species say about their classification?
The more similar the courtship behaviour of two species, the more closely related they are.
Give some reasons why courtship is done.
- Recognise individuals of same species -> Prevents interbreeding
- Identify a mate capable of breeding
- Form a pair bond (e.g. King penguins)
- Synchronise mating -> Greater chance of sperm and egg fusing
- Become able to breed -> Show in physiological state to breed
Give some examples of courtship behaviour.
- Fireflies -> Give off pulses of light.
- Crickets -> Make sounds similar to Morse code.
- Male peacocks -> Show off colourful tails.
- Male butterflies -> Release chemicals to attract females.
Describe courtship behaviour in fireflies.
- Give off pulses of light.
* Pattern if flashes is specific to each species.
Describe courtship behaviour in crickets.
- Make sounds similar to Morse code.
* Code is different for different species.
Describe courtship behaviour in male peacocks.
- Show off their colourful tails.
* This rail pattern is only found in peacocks.
Describe courtship behaviour in male butterflies.
- Use chemicals to attract females.
* Only those of the correct species respond.
What mnemonic can be used to remember the levels of the phylogenetic hierarchy?
Dopey King Prawns Can’t Order Fat Greasy Sausages
How has technology affected taxonomy?
New and improved technologies can result in new discoveries being made and the relationship between organisms being clarified.
Name some technologies used to clarify evolutionary relationships.
• Genome sequencing
• Comparing amino acid sequencing
• Immunological comparisons
(• Morphology)
Describe how morphology can be used to classify organisms.
Structural features of organisms is looked at. Organisms with similar characteristics are assumed to be more closely related.
Describe the pros and cons of morphology as a classification method.
- Pro - Related species can have similar morphology.
* Con - Unrelated organisms can look similar to the same selective pressures.
Describe how genome sequencing can be used to classify organisms.
- The entire base sequence of an organism’s DNA can be determined.
- This can be compared to the base sequence of another organism.
- The higher the percentage similarity between the organisms, the more closely related the species are.
Describe the pros and cons of genome sequencing as a classification method.
- Pro - Species that recently diverged will have a high percentage similarity in their base sequence.
- Con - Expensive.
Is the DNA base sequence the only thing that can be sequenced in organism classification?
No, you can also look at the mRNA sequence.
Describe how comparing amino acid sequences can be used to classify organisms.
- The sequence of amino acids in a protein is coded for by the base sequence in the DNA.
- Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.
- For a given protein, the more closely the amino acid sequence is in two species, the more closely related the species are likely to be.
Describe the pros and cons of amino acid sequence comparison as a classification method.
- Pro - The more amino acids are the same, the more closely related the two species.
- Con - There might not be much difference between the protein’s amino acids as there is less selective pressure on them.
Describe how immunological comparison can be used to classify organisms.
- An antiserum is prepared for a particular species A -> By injecting species A’s serum into another animal (B) that produces antibodies against it.
- This antiserum containing antibodies is added to species C’s serum.
- If the protein antigens are similar in A and C, then the antibodies will bind to proteins and produce a precipitate.
- The more precipitate there is, the more closely related the two species.
Describe the pros and cons of immunological comparison as a classification method.
- Pro - Always forms a precipitate and the more precipitate, the more closely related the species.
- Con - Not precise enough to measure amounts of precipitate.
Remember to practice interpreting data on DNA and protein similarities.
Pg 98 of revision guide.
Traditionally, how could genetic diversity in a population be calculated and why?
- Looking at the frequency of measurable characteristics in a population
- e.g. The number of different eye colours and the number of people with each eye colour
- A wide variety of characteristics suggests a wide variety of alleles and so a high genetic diversity
Describe how modern technologies allow us to calculate genetic diversity in a population.
1) Comparing the DNA base sequence of a single gene in different organisms to find out how many different alleles there are
2) Comparing mRNA sequences and amino acid sequences to find out how many different alleles there are
The more alleles, the greater the genetic diversity.
A higher number of different alleles in a species indicates…
A high genetic diversity.
How have new technologies impacted our understanding of genetic diversity within a population?
New technologies have allowed us to have more accurate estimates of genetic diversity by being able to tell exactly how many alleles there are for a particular gene in a species.
What is variation?
The differences that exist between individuals (between species and within species).
Is variation between species or within species?
Both
What factors can cause variation?
- Genes
- Environment
(These two work in combination)
Describe how genetic factors can cause variation between species.
- Different species have different genes
* This causes variation
Describe how genetic factors can cause variation within a species.
- Individuals have the same genes, but different alleles
* This causes variation within a species
Name some environmental factors that can cause variation within a species.
- Climate
- Food
- Lifestyle
How do genetic and environmental factors affect variation within a species?
Most variation within a species is caused by a combination of genetic and environmental factors.
Give an example of where genetic and environmental factors combine to give variation within a species.
Genes determine how tall an organism can grow but nutrient availability affects how tall the organism actually grows.
When studying variation, do you look at the entire population?
No, you usually take a sample.
How can you make sure that a sample is representative of an entire population?
1) Random sampling
2) Analyse the results statistically + Use a large sample size -> Ensures that any variation isn’t due to chance
Give reasons why a sample may not be representative of an entire population.
- Sampling bias -> i.e. Not random sampling
* Chance -> The individuals may just happen to not be representative
How could you ensure that a sample of plant species in a field is random?
- Divide the field into a grid
* Use a random number generator to select coordinates
How can chance be minimised in a sampling process?
- Large sample size
* Analysis of data collected
Why must the results of a sample be analysed statistically?
- Allows you to check that the variation isn’t due to chance
* So you can be confident that the results are true and reflect the whole population
What is normal distribution?
- A bell-shaped curve that is typical of a feature that shows continuous variation (e.g. height in humans).
- Symmetrical about the mean.
What is skewed distribution?
- Where a normal distribution bell-curve is slightly shifted to one side.
- Not symmetrical.
What is the formula for the mean?
Mean = Sum of all the values / Number of values
What can the mean be used for?
- To check if there is variation between samples
* e.g. Mean height of tree in woodland A was 26m, compared to 32m in woodland B.
What is standard deviation?
A measure of the spread of values in a sample about the mean.
What does standard deviation of a sample tell us?
The variation within the sample.
How is a large standard deviation shown on a bell-curve graph?
The bell-curve is wider.
See diagram of 101 of revision guide
What does a high standard deviation show?
- The data is widely spread.
* The data could be less reliable.
What is the formula for standard deviation for a sample?
s = Root of (Σ(x-xbar)²)/ (N - 1)
Where: • s = standard deviation • Σ = sum of... • x = each value in sample • xbar = mean of the values • N = number of values in sample
How can standard deviation be shown on a bar chart?
- Error bars can be drawn
* They extend one SD above and one SD below each bar
What do error bars on a bar chart tell us?
- The longer the bars, the larger the SD and the more spread out the data is
- If the error bars overlap, we do not have enough evidence to conclude that one mean is certainly greater than another
What happens when the SDs of two means overlap?
There is not enough evidence to support the idea that one mean is greater than the other.
Remember to practice standard deviation on bell-curves and bar charts.
Pg 101 of revision guide.
Why do biologists use standard deviation?
- Reliability -> The larger the SD, the less reliable the data.
- Comparison -> If SDs overlap, then there is no difference between the data as the mean could lie anywhere between those values.
- Variation -> The larger the SD, the higher the variation in that sample.
What is biodiversity?
The variety of living organisms in an area.
What is a habitat?
The place where an organism lives.
What is a community?
All the population of different species in a habitat.
What is genetic diversity?
The variety of different alleles for a gene in a population.
What is species diversity?
- The number of different species (and the numbers of individuals of each species) present in a community.
- Another term for biodiversity.
What is ecosystem diversity?
The range of different habitats, from a small local habitat to the whole of the earth.
Compare genetic diversity and species diversity.
- Genetic diversity -> The variety of alleles for a certain gene in a population.
- Species diversity -> The number of different species (and the number of individuals of each species) in a community.
Biodiversity is often used as a synonym for…
Species diversity
At what scales can biodiversity be considered?
- Local -> Variety of species in a small habitat, e.g. a pond
- Global -> Variety of species on Earth
Is biodiversity the same all around the world?
No, it varies -> Greatest at the equator and decreases towards the poles.
What measures can be used to measure biodiversity and which is better?
- Species richness
- Index of diversity
Index of diversity is better.
What is species richness?
- Number of different species in a community.
* It is a simple measure of biodiversity.
How can you work out species richness?
- Take a random sample of a community.
* Count the number of different species.
What is the difference between species diversity and species richness?
Species diversity factors in for the number of individuals of each species as well as the number of species, while species richness is just the number of species.
i.e. Species diversity is like biodiversity.
What is index of diversity?
- An equation that takes into account both the number of species in a community (species richness) and the abundance of each species (population sizes)
- It is a measure of biodiversity
What is the symbol for the index of diversity?
d
Give the formula for index of diversity.
d = (N(N-1)) / (Σ n(n-1))
Where:
d = index of diversity
N = total number of organisms of all species
n = total number of organisms of each species
Σ = sum of…
The higher the index of diversity value…
The more diverse the area is.
What does a index of diversity value of 1 show?
All the individuals in the area are of the same species.
Calculate the index of diversity for a field with:
• 3 red flowers
• 5 white flowers
• 3 blue flowers
- N = 11
- d = (11(11-1)) / (3(3-1) + 5(5-1) + 3(3-1))
- d = 110 / (6 + 20 + 6)
- d = 3.44
Remember to practise index of diversity calculations.
Pg 102 of revision guide.
Remember to practise the formula for standard deviation and do some examples using it.
Pg 255 of textbook
How do agricultural practices affect biodiversity?
They often reduce biodiversity.
Give some examples of agricultural practices that reduce biodiversity.
- Woodland clearance
- Hedgerow removal
- Pesticides
- Herbicides
- Monoculture
How does woodland clearance reduce biodiversity?
- Reduces the number of of trees and sometimes the number of tree species
- Destroys habitats -> Shelter and food source destroyed
How does hedgerow removal reduce biodiversity?
- Reduces the number of of hedges and sometimes the number of hedge species
- Destroys habitats -> Shelter and food source destroyed
- Hedges may have been used as corridors along which species disperse themselves
Why is woodland clearance done?
To increase the area of farmland.
Why is hedgerow removal done?
To increase the area of farmland.
What are pesticides?
Chemicals that kill organisms that feed on crops.
What are herbicides?
Chemicals that kill unwanted plants.
What is the difference between pesticides and herbicides?
- Pesticides -> Kill organisms that feed on crops
* Herbicides -> Kill unwanted plants
How do pesticides reduce biodiversity?
- Directly kill pests
* Species that feed on the pests lose a food source
How do herbicides reduce biodiversity?
- Kill plants directly
* Species that feed on the weeds lose a food source
What is monoculture?
When farmers have fields containing only one type of plant.
How does monoculture reduce biodiversity?
- Having only a single type of plant reduces biodiversity directly
- A single type of plant can support fewer organisms
What is done in response to agricultural practices that reduce biodiversity?
Conservation schemes are used to protect biodiversity.
Give some examples of conservation schemes.
- Giving legal protection to endangered species
- Creating protected areas such as SSSIs (Sites of Special Scientific Interest) -> Restrict further development, including agricultural development.
- Environmental Stewardship Scheme -> Encourages farmers to conserve biodiversity
Remember to revise agricultural conservation techniques.
Pg 247 of textbook.
