[Y1] Genetic Information, Variation, and Relationships Between Organisms Flashcards
(151 cards)
1
Q
What is a gene?
A
A section of DNA that contains the coded information for making polypeptides and functional RNA.
2
Q
What is a locus?
A
A particular position of a gene on a section of DNA or a chromosome.
(pl: Loci)
3
Q
What can a base sequence of DNA code for?
A
- The amino acid squence of a polypeptide.
- A functional RNA, including rRNA and tRNAs
4
Q
Why must there be a minimum of three bases that code for each amino acid?
A
- Only 20 differnet amino acids regularly occur in proteins.
- Each amino acid must have it’s own code of bases on the DNA.
- Only four different bases are present in DNA.
- If each base coded for a different amino acid, only four different amino acids could be coded for.
- If a pair were used, 16 (4²) different codes are possible, which is still inadequate.
- If three bases were used, 64 (4³) different codes, more than enough to satisfy the 20 amino acid requiremnt.
In fact some amno acids have more than one triplet.
5
Q
How does code for a polypeptide bengin and end?
A
- The start of a DNA sequence that code for a polypeptide is always the same triplet coding for the amino acid methionine. If this isn’t in the polypeptide then it is removed later.
- There are three non coding triplets, these are stop triplets and make the end of a polypeptide chain.
6
Q
What is degenerate code?
A
When an amio acid can be coded for by more than one different triplet. (can be 2-6 different triplets.
(although a few are coded by one codon)
7
Q
How is the nature of code in DNA indirect evidence of evolution?
A
The code is universal (with a few minor exceptions), as each triplet codes for the same amino acid in all organisms.
Therefore it suggest that all organisms have an ancestor where this trait began.
8
Q
When does code overlap?
A
Never.
Each base pair is only read once when and so the DNA 123456:
- is read as 123 and 456
- NOT 123, 234, 345, 456.
9
Q
What is an exon and intron
A
Exons: coding sequences of DNA.
Introns: non-coding sequences of DNA.
10
Q
What are the differnces between prokaryotic and eukaryotic DNA?
A
Prokaryotic: DNA is much shorter, form a circle, and are not associated with protein molecules (histones).
Eukaryotic: DNA is much longer, form a line (linear). and occur in assoation with proteins called histones to form a chromosome. The mitochondria and chloroplasts also contain DNA which is like that of the prokaryotic DNA.
11
Q
What do histones do?
A
They fix the DNA into position.
12
Q
How many molecules of DNA make up a chrmosome?
A
One.
It is very long and is coiled up many times.
13
Q
How do chromosomes vary between species?
A
chromosomes differ in number (in typical indiviuals in a species, ignoring mutations such as down syndrome)
E.g humans have 46 chromosomes whilst dogs have 78.
(this number is usually even in adult cells)
14
Q
What are homologous pairs?
A
Chomosomes of that have the same gene loci (but can be different alleles), one maternal, the other paternal.
15
Q
What is diploid?
A
2 of each chromosome.
2n
16
Q
What is haploid?
A
1 of each chrmosome.
n.
17
Q
What is an allele?
A
One of a number of alternative forms of a gene.
18
Q
What is a mutation?
A
Any change in the quantity or base sequence of a gene.
May or may not produce a new allele of that gene and result in a different sequence of amno acids being coded for.
19
Q
Why might a mutation have serious consequneces for an organism?
A
The diffence in sequnce of amino acid as a result of a new allele will lead to the production of a differnt amino acid, hence a differnt protein.
A different proten may not function properly or not at all
If the protein produced in an enzyme, it may have a different shape. The new shape may not fit the enzyme’s substrate.
As a result the enzyme may not function, having serious consequences on an organism.
20
Q
Where does protein systhesis take place?
A
The cytoplasm.
21
Q
How does genetic code get to the site of protein synthesis? Why is this possible?
A
Via mRNA.
mRNA is small enough to leave the nucleus through nuclear pores and enter the cytoplasm.
22
Q
Define codon.
A
A sequence of three basees on mRNA that code for a single amino acid.
23
Q
Define genome.
A
The comlete set if genes in a cell, including those in mitochondria and/or chloroplasts.
24
Q
Define proteome.
A
The full range of proteins produced by the genome.
(sometimes called complete proteome, where proteome refers to the proteins produced by a given type of cell under a certain set of conditions.)
25
What is the structure of RNA?
- A polymer made up of repeating mononucleotide sub-units. A nucleotide of RNA consists of:
- the pentose sugar ribose.
- one of the organic bases (A, U, G, C).
- a phosphate group.
26
What RNA is important in protein synthesis?
- mRNA
| - tRNA
27
Describe the stucture of mRNA and tRNA.
mRNA:
- thousonds of mononucleaotides in a long single helix.
- its base sequence is determined by the sequence of bases on DNA
- great variety in different mRNA
tRNA:
- small molecule, made up of around 80 nucleotides.
- single stranded folded into a cover-leaf shape.
- one end extendeds beyond the other where the amino acid can easily attach.
- at the opposite end there are three other organic bases called an anticodon.
- There are as many different varieties as there is coding triplets.
- Each has an anticodon specific to one amino acid.
28
What is the complimentary base paring between bases?
Guanin to Cytosine
Adenine to Uracil (RNA) or Thymine (DNA).
29
What are the overall steps of protein sythesis?
- DNA provides the instructions in the form of a long sequence of bases.
- A complimentary section of part of this sequence is made in the form of pre-mRNA. (Transcription)
- Pre-mRNA is spliced into mRNA. (Splicing)
- The mRNA is used as a template to which complimentary tRNA molecules attach and the amino acids they carry link to form a polypeptide. (Translation)
30
Describe the process of transcription.
- An enzyme acts on a spesific region of the DNA causing the two strands to separate and expose the nucleotide base in that region
- The nucleotide bases on one of the template strand pair with complimentary nucleotides (A to U, T to A, G to C, C to G) from the pool which is present in the nucleus.
- RNA polymerase moves along the strand and joins the nucleotides together to form pre-mRNA adding them one at a time.
- DNA strands rejoin behind it, so few base pairs are exposed at one time (around 12).
- When RNA polymerase reaces a particular sequence of bases on the DNA that is recoginsed as a 'stop' triplet code, it detaches.
31
What is the difference between transcription in prokayotes to eykaryotes?
The result of transcription in prokaryotes is mRNA, but in eukaryotes is pre-mRNA.
Therefore splicing is only required in eukaryotes.
32
What happends during splicing?
Introns are removed from pre-mRNA and the exons are joined together, resulting in mRNA.
33
Why does splicing need to take place?
The introns would prevent the sythesis of polypeptides.`
34
When will mRNA diffuse out of the nucleous?
Never, as it is to large.
Instead it leaves via nuclear pores
35
What happends to the mRNA once it leaves the nucleaus?
It is attracted to the ribosomes to which it attaches to.
36
How many different tRNA are there?
Around 60.
37
Describe the process of translation.
- A ribosome becomes attached to the starting codon at one end of the mRNA molecule.
- tRNA with the complimentary anticodon moves into the ribosome and pairs up with the codon on the mRNA.
- This tRNA carries a specific amino acid.
- Anther tRNA with the complimentary anticodon pairs with the next codon on the mRNA.
- This tRNA carries another specific amino acid.
- The two amino acids on the tRNAs are joind by a peptide bond using an enzyme and ATP, which is hydrolysed to provide energy for the condensation reaction.
- The ribosome moves along to the third codon on the mRNA, again linking the amino acids but from the 2nd and 3rd tRNA.
- As this happens, the first tRNA is released from its amino acid, and is free to collect another amino acid from the amino acid pool in the cell.
- This process continues, with up to 15 amino acids being added per second, until the polypeptide is built up, and it reaches a stop codon.
- The ribosome separates from the mRNA
- Up to 50 ribosomes can pass immediatley behind the first ro many poypeptides can be assembled simultaneously.
38
What might happen after translation?
- The polypeptide is coiled or folded, producing a secondary structure.
- The secondary structure is folded, producing a tertiary structure.
- Different polypeptide chains, along with non-protein groups, are linked to form a quaternary structure.
39
When can gene mutation arise?
Sponataiouly during DNA replication.
40
Describe the types of mutation.
- Substituion of bases:
A gene mutation where a nucleotide in DNA is replaced by another nucleotide that has a different base.
- Deletion of bases:
A gene mutation where a nucleotide is lost from the normal DNA sequnece.
41
How severe is gene mutation by substitution?
Depends on the precise nucleotide substituted.
- The nucletoide may be an intron and so have no effect on the protein produced.
- The nucleotide may code of the same protein (as a result of degerneate code) and so also not have an effect.
- The nucleotide may code for a protein that vastly effects the tertiary structure of the protein, hugly effecting the organisms (e.g if its an enzyme).
42
How severe is gene mutation by deletion?
Can have extreme consiquences, as it casues all nucleotides after it to move one to the left when being read. Not only effecting that one triplet but also every triplet after it.
43
What is a chromosome mutation?
A change in the structure or number of whole chromosomes.
44
Describe the form chromosome mutations can take?
- Changes in whole sets of chromosomes:
The organism may have three or more chromosomes instead of two (polyploidy)
- Changes in the number of individual chromosomes:
Occurs when individual homologous pairs fail to separate during meiosis (non-disjunction), resulting in organisms having one more or one fewer chromosome.
45
What can non-dijuction lead to after fertilisation?
On fertiliasation with a regular gamete, the resultant offspring have more or fewer chromosomes than normal in all their body cells.
(e.g. Down Syndrome is an additional chromosome 21.)
46
What is the difference between mitosis and meiosis.
- Mitosis: produces two daughte cells with the same number of chromosomes as the parent cell and as each other.
- Meiosis: produces four daughter cells, each with half the number of chromosomes as the parent cells
47
What happens during sexual reproduction?
Two gametes fuse to give rise to a new offsprig.
48
What is an important property of a gamete?
They are haploid.
| in most cases
49
What would happen if a gamete was diploid?
The number of chromosomes would be 92 imeadatly after sexual reproduction (42 from each gamete).
This doubling would increase in each generation exponentially.
This is avoided by gametes being haploid.
50
What happens overall during meiosis?
Homologuos pairs of chromosomes seperate, so that only one chromosome from each pair enters the daughter cell.
51
What happends durineg each meiotic division?
Meiosis 1:
- Homologous chromosomes pair up and their chromatids wrap around each other.
- Here crossing over may occur.
- Homologous pairs separate, with one chromosome from each pair going into one of the two daughter cells.
Meiosis 2:
- Chromatids move apart.
- 4 daughter cells have usually been formed.
52
Other than halving the number of chromosomes, what is achieved as a result of meiosis?
Genetic variation among offspring, which may lead to adaptations that improve survival chances.
53
How does meiosis cause genetic variation?
- Independaent segregation of homologous chromosomes.
| - New combinations of maternal and paternal allels by crossing over.
54
What is meant by independent segregation?
- During meiosis 1, homologous pairs arange themselves in lines randomly.
- One of each pair will pass to each daughter cell.
- Which one of the pair goes into one daughter cell, and which one goes into the other, depends on how the pairs line up.
- Since they line up, the combination of chromosomes of maternal and paternal that go into the daughter cells (at meiosis 1) is also matter of chance.
55
Why does variety occur as a result of independent assortment.
- Each chromosome in a homolous pair has the same gene and so determine the same characteistic.
- But the alleles of the genes may differ.
- And so the independent assortment of these chromosomes produce new genetic combinations.
56
Homologous chromosomes coding for toungue rolling lines up bellow the homologous chromosomes that code for blood group.
There are two arrangements P and Q.
Arrangement P:
- has non-roller and blood type A on one side
- and roller and blood type B on the other side.
Arrangent Q:
- has roller and blood type A on one side
- and non-roller and blood type B on the other.
What are the possible gametes for each arrangement?
Arrangement P:
- 2 roller/B gametes
- 2 non-roller/A gametes
Arrangement Q:
- 2 non-roller/B gametes
- 2 roller/A gametes
Therefore genetic variation can occur as a result of independent segregation.
57
How and why do haploid gamates fuse?
- How: randomly at fertilisation.
| - Why: to restore the diploid state after meiosis.
58
What happens during genetic recombination by crossing over?
- The chromatids of each pair twist around one another.
- During this process tension builds up and portions of the chromatids break off.
- These broken portions might then rejoin with the chromatids of its homologous partner.
- Usually it is the equivalent portions of homologous chromosomes that are exchanged.
- In this way new genetic combinations of material and paternal alleles are produced.
59
What happens as a result of meiosis if recombination by crossing over happens as opposed to it not happening?
If it happens: You get 4 different genetic compositions.
If it doesn't happen: You get 2 different genetic compositions (2 times each).
60
How do you calculate the number of possible combinations of chromosomes in any daughter cell as a result of meiosis?
How many possible combinations of chromosomes can you have in a organism with 4 homologous pairs, as a result of meiosis?
2ⁿ, where n = the number of homologous pairs.
An oganism with 4 homologous pairs can produce 2⁴ possible different combinations of chromosomes of maternal and paternal origin in its daughter cells as a result of meiosis.
2⁴ = 16 possible different combinations of homologous pairs.
61
How do you calculate the number of possible combinations of chromosomes in an offspring produced as a result of sexual reproduction?
(2ⁿ)², where n = the number of homologous pairs.
62
Why might the cacluated value for possible homologous chromosome combinations be smaller than what is actually observed?
Due to random crossing over between chromatids during meiosis 1 exchanging via recombination.
63
Calculate the number of possible chromosome combinations produced from the fertilisation of two gametes from separate individuals whos diploid number is 12 (assume no crossing over).
Because you are looking at possible chromosomes after fertilisation:
(2ⁿ)², where n = the number of homologous pairs.
diploid number = 12 therefore there are 6 homologous pairs.
n = 6
(2⁶)² = 4096
64
What is genetic diversity?
The total number of different alleles in a polulation.
65
What is a population?
A group of individuals of the same species that live in the same place and can interbreed.
66
Why is an increased genetic diversity beneficial?
- The greater teh genetic diversity, the more likely that some individuals in a population will survive an environmental change.
- Beacuse there is a wider range of alleles and therefore a wider range of characteristics.
- This gives a greater probability that some individuals will possess a characteristic that suits it to the new environmental conditions.
67
Why are not all alleles of a population equally likely to get passed on?
Because only certain individuals are reproductivly successful and so pass on their alleles.
68
How does the difference between reproductive sucess of individuals affect allel frequencies in populations?
- Within any population there will be a gene pool with a wide variety of alleles.
- Random mutation of alleles within the gene pool may result in new alleles of a gene, which in most cases harmful.
- In certain environments, the new allele of a gene may be advantageous for its possessor over other individuals in a population.
- These individulas will be better adapted and so more likly to survive competition with others.
- And so are more likly to obtain the available recousres and so grow quicker and live longer.
- As a result have a better chance of breeding successfully and producing offspring.
- Only individuals who reproduce successfully will pass on their allels to the next generation.
- Therefore the new allele that gave the parent an advantage in competition is most likely to be passed on to the next generation.
- As the new individual (from the next gen) also have the new 'advantageous' allele, they are also more likly to survive, and so reproduce successfully.
- Over many generations, the number of individuals with the new 'advantageous' allel will increase at th expense of the individuals with the 'less advanatageous' alleles.
- Over time, the frequnecy of the new, 'advantageous' allele in the population increase while that of the 'non-adantageous' ones decrease.
69
What determines what is 'advantageous'?
Environmental conditions.
70
What is selection?
- The process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.
- Every organism is subjected to a process of selection, based on its suitability for surviving the conditions that exist at the time.
71
What are two types of selection?
- Directional: favours individuals that vary in one direction from the mean of the population. This changes the characteristics of the poulation.
- Stabilising: favours average individuals and preserves the characteristics of a population.
72
What are polygenes?
Multiple genes that influence more than one characteristics.
73
Which of characteristics effected by polygenes OR characteristics affected by a single gene is more influenced by the environment?
Polygenes. The effect it has is that it produces individuals in a population that vary about the mean.
74
What happnes when variation of a spesific trait is plotted on a graph?
You see a normal distribution curve.
75
What is a phenotype?
The observable physicsal and biochemical characteristics of an organism.
76
How does directional selection take place?
- A spontaneous mutation occurs in the alleles in an organism, casuing it to fall either left or right of the mean in a normal distribution curve, that enables it to be better suited to an environment either side of that of the mean.
- By chance, the organism is in a situation where this mutation is more advantageous over the alleles that are not mutated and so its phenotype better suits the new conditions
- This makes the organsim more likely to survive, and thus more likely to reproduce.
- Therefore they are more likely to contribute more offspring (and the alleles these offspring possess) to the next generation than other individuals.
- Over time, the frequency of the benefitial mutation increases within the population, out competing those without the allele.
- The populations normal distribution curve therefore shifts in the direction of a population having the allele suited to the environment change.
77
Using the example of bacterial resistance, describe how directional selection takes place within a population?
- A spontaneous mutation occurrs in the allele of a gene in a bacterium that enables it to make a new protein - an enzyme that allows it to break down penecilin before it kills the bacteria - penecilinase.
- The bacterium happens by chance, to be in a situation where penecilin is being used to treat an individual. Here the mutation gives the bacterium an advantage in survival, as it can break down the antibiotic, and survive while the rest of the population are killed by it.
- The bacterium that survive are able to divide by binary fission to build up a small population of penicillin resistant bacteria.
- Members are more able to survive, and thus multiply, , even in the presence of penicillin than the non-resistant population.
- The resistant population increases at the expense of the non-resistant population. Consequently the frequency of alles that enable the production of penicillinase increases in the population.
- The population's normal distribution curve shifts in the direction of ta population having grater resistance to penicillin.
78
When can direction selection take place?
When the environmetnal conditions change.
79
When can stabilising selection take place?
When the environmental conditions remain stable.
80
How does stablising selection take place?
- The optimimum phenotype for an environmental condition becomes a mean when the environmental conditions are stable.
- Those that are closer to the mean, are closer to the optimum phenotype.
- If an organism has the optimum phenotype they are more likely to survive and thus more likely to live til reproduction.
- They are therefore more likely to pass on their optimal alleles successfully to the next generation and contribute more offspring to that generation.
- Those with more extreme phenotypes, that are spread wide from the mean and not favoured, are at a greater disadvantage when competing in the stable environment.
- They are therefore less likely to survive, and thus less likely to reproduce and pass on their unfavourable alleles to the next gerneation.
- Overtime, if the conditions remain constant, the optimum pheonotype is preserved, and the number of individuals with the optimum phenotype increases - both at the cost of the unfavoured penotypes.
- As a result the preak is higher and the spread becomes narrower on the normal distribution curve.
81
In what ways could individulas/species be better adapted to the environmental conditions they live in?
- Anatomical (e.g. shorter ears and thicker fur in artic foxes than foxes in warmer climates)
- Physciological (e.g. oxidising fats rather than carbs in kangaroo rats to produce additional water in a dry desert environment)
- Behavioral (e.g. the autumn migration of swallow from the UK to Africa to avoid food shortages in the UK winter)
82
What is classification?
The organisation of organisms into groups.
83
What is the one main thing memebers of the same species have in common?
They are capable of breeding to produce living, fertile offspring.
84
What system of naming species did Carl Linnaeus divise?
The Bionomial system of naming species, where organism are identified by two names.
85
What are the features of the binomial system?
- Its a universal system based upon latin or greek names.
- The first name, called the generic name, denotes the genus to which the organsim belongs.
- The second name, called the specific name, denotes the species to which the organism belongs and is never shared by other species within the genus.
86
What are the rules applied to the binomial system in scientific writing?
- Printed in italics OR (if handwitten) underliend to indicat they are scientific names.
- The first letter for the generic name is upper case, but thee specific name is lower case.
- If the generic name is not known, it can be written as 'sp' (e.g 𝘍𝘦𝘭𝘪𝘹 𝘴𝘱.)
87
As knowledge of ___ increases, the classification of the species changes.
- An organisms evolution.
- An organisms phyical features.
- An organisms biochemistry.
- An organisms behaviour.
88
What is courtship behaviour?
Genetically determine displays of behaviour that result in mating and eventual reproduction.
89
What is the importance of courtship behaviour?
It ensures mating is sucessful and that offspring have the maximum chance of survival.
90
In which ways do courtship behaviour enable individuals to mate sucesfully and ensure offspring have the maximum chanve of survival?
- Enables individuals to recognise members of their own species: so they only mate within their species to be able to produce fertile offspring.
- Enables individuals to identify mate that is capable of breeding: as both individuals need to be sexually mature, fertile, and receptive to mating.
- Enables individuals to form a pair bond: that will lead to successful mating and rating of offspring.
- Enables individuals to synchronise mating: so it takes place when there is the maximum probability of the sperm and egg cells meeting.
- Enables individuals to become able to breed: by bringing members of the opposite sex into a physiological state that allows breeding to occur.
91
Describe an instance of courtship behaviour where a male seeks out a female to mate with.
- Females of many species undergo a cycle of sexual activity in which they can only conceive during a very short time.
- They are often only receptive to mating for a period around the time when they oriduce eggs.
- Courtship behaviour is used by males to determine whether the female is at this receptive stage.
- If she responds with the appropriate behavioural response, courtships continue and is likely yo result in the production of offspring.
- If she is not receptive, she exhibits a different pattern of behaviour and the male ceases to court her, turning his attention elsewhere.
92
What is the difference between classification and taxonomy?
The grouping of organisms is know as classification, while the theory and practise of biological classification is called taxonomy.
93
What are the two main forms of biological classification?
Artificial calssification:
- Divides organisms accordign to differences that are useful at the time (e.g colour, size, number of legs, leaf shape).
- These are described as analogous charateristics.
Phylogentic classification:
- Based upon evolutionary relationships between organisms and their ancestors.
- Classifies species into groups using shared features derived from their ancestors.
- Arranges the groups into a hierary, in which the groups are contained within larger composite groups with no overlap.
94
What are analogous characteristics?
Characteristics where they have the same function but do not have the same evolutionary origins.
(e.g. wings of butterflies and birds are both for flight but they originated in different ways)
95
What are homologous characteristics?
Charateristics wher they have similar evolutionary origins regardless of their functions in the adults of a species.
(e.g. wings of birds, arms of humans, and the front legs of a horse all have the same basic structure and evolutionary origins.)
96
What is a group within a phylogenetic biological classification called?
A taxon.
| pl. Taxa
97
What is the highest taxanomic rank?
A domain.
98
What are the 3 domains?
- Bacteria.
- Archaea.
- Eukarya.
99
What are features of individuals within the domain Bacteria?
- The absence of membrane-bounded organelles such as a nuclei or mitochondria.
- Unicellular, although cells may occur in chains to clusters.
- Ribosomes are smaller (70s) than in eukaryotic cells.
- Cell walls are present and made of murein.
- Single loop of naked DNA made up of nucleic acids but no histones.
100
What are features of individuals within the domain Archaea that make them different to those that are Bacteria?
- Their genes and protein sythesis are more similar to eukaryotes.
- Their membranes contain fatty acid chains attached to glycerol by ether linkages. (NOT ester like in Eukarya)
- There is no murein in their cell walls.
- They have a more complex form of RNA polymerase.
101
What are features of individuals within the domain Eukarya?
- Their cells posses membrane-bounded organelles (e,g, mitochondria, chloroplasts)
- Their membranes contain fatty acid chains attached to glycerol by ester linkages.
- Not all possess cells with a cell wall, but where they do it contains no murein.
- Ribosomes are larger (80s) than in Bacteria and Archea.
102
What four kingdoms are the Eukarya domain divided into?
- Protoctista
- Fungi
- Plantae
- Animalia
103
What is the largest grouping within a kingdom?
Phyla.
104
How are organsism of different phyla different?
Their body plan is radically differnt from organisms in any other phylum.
105
What does diversity within a phylum divide it into?
Classes.
106
How are classes divided?
Orders.
107
How are orders divided?
Families.
108
How are families divided?
Genera.
109
How are genera divided?
Species.
110
List al lof the phylogentic ranks within the domain Eukarya?
- Kingdom
- Phylum.
- Class.
- Order.
- Family.
- Genus.
- Species.
111
What is phylogeny?
The evolutionary releationship between organisms.
112
How are phylogenetic relationsips of differnt speciees represented?
Through phylogenetic trees.
113
What are the features of a phylogenetic tree?
- The oldest species is at the base of the tree.
- The most recent species are represented by the ends of the branches.
- The closer the branch the closer the evolutionary relationship.
114
What is biodiversity?
The range and veriety of genes, species and habitats within a particular region.
115
What is species diversity?
The number of different species and the number of individuals of each species within any one community.
116
What is genetic diversity?
The variety of genes possessed by the individuals that make up a population of a species.
117
What is ecosystem diversity?
The range of different habitats, from a small local habitat to the whole of the Earth.
118
What is species richness?
A measurement of species diversity that looks at the number of different species in a particular area at a given time (community).
Two communities may have the same number of species but the proportions of the community made up of each species may differ markedly.
119
What is one way of measuring species diversity?
Index of diversity equtation.
d= (N(N-1)) / ∑n(n-1)
120
What are the factors needed to calculate the index of diversity?
d= (N(N-1)) / ∑n(n-1)
d : index of diversity
N: total number of organisms of all species
n: total number of organsims of each speacies.
121
What does the number given by the index of diversity tell you?
The higher the number 𝘥, the greater the species diversity.
122
How does agriculture lead to a low index of diversity?
- As natural ecosystems develop over time, they become complex communities.
- These communities have a high index of diversity.
- Agricultural ecosystems controlled by humans often select sprecies for particular qualities that make them more productive to them.
- As a result both the number of species and the genetic variety of alleles they posses are reduced to the few that have the desired phenotype.
- To be economic the number of individuals of these desirable species needs to be large.
- Any particular area can only support a certain amount of biomass.
- If most of the area is taken up by the one species the farmer considers desirable, there is a smaller area available for all other species.
- These other species must then compeate for the little space and resources available (more so than before).
- Many do not survive this competition and those with trates that have evolved to adapt to the change, their population is considerable reduced.
- Pestisides are also used to exclude these species, as they compete for the light, mineral ions, water, and food required by the farmed species.
- Therefore there is a reduction is species diversity, and a low index of diversity in the agricultural ecosystem.
123
What is the overriding effect of intesive food production?
The diminishing of habitats within ecosystems (and thus a reduce in species diversity).
124
What practices have directly removed habitats and reduced species diversity?
- The removaal of hedgerows and grubbing out woodlands.
- Creating monocultures (e.g. replacing natural meadows with cereal crops or grass for silage).
- Filling in ponds and draining marsh and other wetland.
- Over-grazing of land (e.g. upland areas by sheep thereby preventing regeneration of woodland.)
125
What practices have indirectly removed habitats and reduced species diversity?
- The use of pesticides and inorganic fertilisers.
- The escape of effluent from silage stores and slurry tanks into water courses.
- The absence of crop rotation and lack of intercropping or undersowing.
126
What management techniques can be applied to increase species and habitat diversity, without unduly raising food costs or lowering yield?
- Maintain existing hedgerows at the most beneficial height and shape (A-shaped provides a better habitat than a rectangle one.)
- Plant hedges rather than erect fences as field boundries.
- Maintain existing ponds and where possible create new ones.
- Leave wet corners of fields rather than draining them.
- Plant native trees on land with a low species diversity rather than in species rich areas.
- Reduce the uce of pesticides - use biological control where possible or genetically modified organisms that are resistant to pests.
- Use organic, rather than inorganic fertilisers.
- Use crop rotation that includes a nitrogen fixing crop, rather than fertilisers, to improve soil fertility.
- Use intercropping rather than herbicides to control weeds and other pests.
- Create natural meadows and use hay rather than grasses for silage.
- Leave the cutting of verges and field edges until after flowering and when seeds have dispersed.
- Introduce conservation headlands - areas at the edges of fields where pesticides are used restrictively so that wild flowers and insects can breed.
127
How was genetic diversity measured traditionally?
By observing the characteristics of organisms.
This was based on the fact that each observable characteristic is determined by a gene or genes.
The variety within a characteristic depends on the number and variety of alleles of that gene.
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What are the limitations with the traditional means on measuring genetic diversity?
- A large number of observational characteistics are polygenic (coded for by more than one gene) so they are not discrete from one another but rather vary continuously. This makes it difficult to distinguish one from another.
- Characterisitcs can be modified by the environment. Thus a difference may be the result of different environmental conditions rather than different alleles.
129
How has the traditional means of measuring genetic diversity changed?
From infering DNA differences from observable characteristrics to directly observing DNA sequences themselves (made possible by advances in gene technology made over the years).
130
How does DNA sequencing work?
Done by automatic mechines on DNA, that tags a nucleotide with a different floresent dye - Adenine (green), Thymine (red), Cytosine (blue), Guamine (yellow) - producing a series of coloured bands.
This allows us to determin the exact order of nucleaotides on DNA.
131
How is DNA sequnecing used in measuing genetic diversity?
Analysis of sequnecing oatterns can be compared with another idividual within the same species or a different species to determin how diverse they are.
132
Why isn't measuring genetic divesity by DNA seqencing done by the human eye? What is done instead?
It would be too slow.
Instead it is scanned by lasers and interpreted by computer software to give DNA nucleotide base sequences in a fraction of the time.
133
What would we expect to see in sequnecing data in similar species and why?
- When species give rise to another species during evolution the DNA of the new species will initilly be very simila.
- As a result of random mutations, the sequences of nucleotide bases in the DNA of the species will change.
- Over time the new species will accumulate more and more differences in its DNA.
- Therfore, we would expect to see species that are more closly related to show more similarities in their DNA base sequence than species that are more distantly related.
134
Why can mRNA be used to measure genetic diversity?
The base sequence of mRNA is complimentary to those of the strand of DNA from which they were made.
So we can measure DNA diversity, and thus genetic diversity, by comparing the base sequence if mRNA.
135
Why can amino acid sequences in proteins be used to measure genetic diversity?
The sequence of amino acids in proteind is determined by mRNA which, in turn, is determined by DNA.
Genetic diversity within, and between, species can therefroe by measured by comparing the amino acid sequeces of their proteiens.
136
What three ways are used to measure genetic divesity?
Comparing...
- DNA base sequencing data
- base sequences of mRNA
- amino acid sequences in proteins
137
What does the degree of similarity in the amino acid sequence of the same protein in two different species reflect?
How closely related the species are.
138
How can amino aicd sequences be comapred?
By looking at both how similar they are and how different they are.
139
What is interspecific variation?
Variation between different species.
140
What is intraspecific variation?
Varitation between individuals within the same species.
141
What is random sampling?
Taking measuremtns of individuals, selected from the poulation of organisms which is being investigated.
142
Why might random sampling not be reliable?
- Sampling bias: The seector may be making unrepresentative choices, wither delibratly or unwittingly.
- Chance: Even if sampling bias is avoided, individuals chosen may, by pure chance, not be representative.
143
Give one method of random sampling to eliminate sampling bias?
1. Divide the study area into a grid of numbered lines.
2. Using random numbers, from a table or generated by a computer, obtain a series of coordinates.
3. Take samples at the intersection of each pair of cooridinates.
144
How can we minimise the effect of chance when randomly sampling?
- Using a large sample size: The more idividuals that are slected the smaller the probibiblity that chanve will influece the result, and the less influence anomolies will have.
- Analysing the data collected: By accepting that chance will play a part, the data collected can be analysed using statisical tests to determin the extent to which chance may have influenced the data.
145
What does a normal distribution curve normally show show?
Contiueous variation.
146
What is it called when a bell-shaped cureve is shifted to either side of a central value?
A skewed distribution curve.
147
What three terms are associated with normal distribution curves?
(arithmetic) mean: The sum of the sampled values devided by the number of items.
mode: The single value of a sample that occure most often
median: The central or middle vale of a set of values when the values are arranged in ascendig order.
148
How can normal distribution curves differ?
- Mean: The measurment of maximum hight.
| - The stadard deviation: width of the curve (the range of values either side of the mean to the point of inflection)
149
What is the point of inclection?
The point at which a normal disticbution curve changes from being convex to concave.
150
What is the formula for the stadard devation?
s = √( Σ(x-x̅)² / n-1 )
```
x = measured value (from the sample).
x̅ = mean value of x.
n = total number of values in the sample.
```
151
How many significant figures should answers be given to?
The same number of significant fig as the data you are given or are using (unless it specifies).
Be careful not to round prematurely however.
