T4: Genetic Information & Variation Flashcards

1
Q

What are the components of nucleotides?

A
  • pentose sugar
  • phosphate group
  • an organic nitrogenous base
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2
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2)

A
  1. Condensation (reaction)/loss of water;
  2. (Between) phosphate and deoxyribose;
  3. (Catalysed by) DNA polymerase;
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3
Q

In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.
Describe how the separation of strands occurs. (2)

A
  1. DNA helicase;
  2. Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases
    OR
    Breaks hydrogen bonds between polynucleotide strands;

Reject hydrolysis of hydrogen bonds

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4
Q

The nucleus and a chloroplast of a plant cell both contain DNA. Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus. (3)

A

In chloroplasts:
1.   DNA shorter;
Accept smaller
2.   Fewer genes;
3.   DNA circular not linear;
4.   Not associated with protein/histones, unlike nuclear DNA;
5.   Introns absent but present in nuclear DNA;

Must be comparative statements.

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5
Q

DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2)

A
  1. Hydrogen bonds between the base pairs holds two strands together
  2. Many hydrogen bonds provides strength
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6
Q

Describe FOUR differences between the structure of a tRNA molecule and the structure of an
mRNA molecule. (4)

A
  1. tRNA is ‘clover leaf shape’, mRNA is linear;
  2. tRNA has hydrogen bonds, mRNA does not;
  3. tRNA has an amino acid binding site, mRNA does not;
    Accept ‘CCA end’ for amino acid binding site
  4. tRNA has anticodon, mRNA has codon;

Must be a comparison

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7
Q

what is a codon?

A
  • triplets of bases that code for a particular amino acid
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8
Q

What is the genetic code?

A
  • the order of bases on DNA
  • ## consitsts of codons ( triplets of bases that code for a particular amino acid)
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9
Q

Why is the genetic code described as being universal? (1)

A
  • (In all organisms / DNA,) the same triplet codes for the same amino acid;
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10
Q

Define a gene

A
  • a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
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11
Q

give the functions of the three types of RNA.

A

mRNA - the bases are used by ribosomes to form polypeptide chains
tRNA - carries amino acids to the ribosome
rRNA - ribosomal RNA molecules form part of the structure of ribosomes

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12
Q

Identify and define features of the genetic code.

A
  1. non-overlapping : each triplet is only read once / each base is part of only one triplet
  2. degenerate: more than one triplet codes for the same amino acid.
  3. Universal = the same triplet codes for the same amino acid in all species

1, E.g. ACA ATA not CAA TA or AAT

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13
Q

What is a locus?

A
  • fixed position on a DNA molecule occupied by a gene
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14
Q

What is an allele?

A
  • different versions of the same gene found at the same locus on a chromosome.
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15
Q

Define exons and introns

A

exons: Base/ triplet sequence coding for polypeptide/sequence of amino acids
Introns: regions of DNA that do not code for anything. ( non-coding DNA)

exons: regions of DNA that code for amino acid sequences

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16
Q

Where are introns found?

A
  • between exons
  • within genes
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17
Q

Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer

A
  1. (Because) base/nucleotide sequence;
  2. (In) triplet(s);
  3. (Determines) order/sequence of amino acid /primary structure (in polypeptide);
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18
Q

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)

give similarities also!!

A
  1. Nucleotide structure is identical;
  2. Nucleotides joined by phosphodiester bond;
  3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
    Contrasts:
  4. Eukaryotic DNA is longer;
  5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
  6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
  7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;
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19
Q

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. (2) Give two reasons why.

A
  1. Triplets code for same amino acid
    Accept: DNA/code/triplets are degenerate
    Reject: codons (as question states within genes)
  2. Occurs in introns /non-coding sequence;
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20
Q

Define the terms:
genome
proteome

A

genome: the complete set of genetic information contained in the cells of an organism
proteome: full) range of / number of different proteins that a cell is able to produce/ DNA is able
to code for (at a given time)

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21
Q

Describe the structure of mRNA.

A
  • long , linear , single strand.
  • It is made up of a sugar-phosphate backbone and exposed unpaired bases
  • Uracil bases are present instead of thymine bases
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22
Q

Suggest the advantages of using mRNA rather than DNA for translation

A
  • shorter & contains uracil so no excess polypeptide forms
  • single-stranded & linear = ribosome moves along strand & tRNA binds to exposed bases
  • contains no introns
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23
Q

Describe the structure of tRNA

A
  • tRNA is a single-stranded molecule
  • It has a sugar-phosphate backbone
  • It has a folded , CLOVER LEAF shape
  • has anticodon complemenrary to codon on MRNA
  • has amino acid binding site
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24
Q

In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules.

A
  1. mRNA has fewer nucleotides
    Pre-mRNA more nucleotides
    OR
    mRNA has no introns/has (only) exons
    OR
    Pre-mRNA has (exons and) introns;
  2. (Because of) splicing

Accept mRNA is shorter OR pre-mRNA is longer

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25
Q

Describe how mRNA is formed by transcription in eukaryotes (5)

A
  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. Free RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA)
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA by removing introns using enzyme splicesome
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26
Q

Describe how a polypeptide is formed by translation of mRNA (6)

A
  1. mRNA attaches) to ribosomes or RER ( ribosome moves to start codon)
  2. tRNA brings a specific amino acid;
  3. (tRNA) anticodons (bind to) complementary (mRNA) codons;
  4. Amino acids join by peptide bonds;
  5. (Amino acids join together) with the use of ATP; and peptidyl transferase enzyme
  6. tRNA released (after amino acid joined to polypeptide);
  7. The ribosome moves along the mRNA to form the polypeptide until stop codon is reached

peptidyl transferae

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27
Q

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer

A
  1. mRNA associates with a ribosome / ribosome attaches to mRNA;
  2. Ribosome moves to / finds the start codon / AUG;
  3. tRNA brings / carries (appropriate / specific) amino acid;
  4. Anticodon (on tRNA complementary) to codon (on mRNA);
  5. Ribosome moves along to next codon;
  6. (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide);
    using) ATP
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28
Q

Describe how mRNA is produced from an exposed template strand of DNA. Do not include DNA helicase or splicing in your answer

A
  1. (Free RNA) nucleotides form complementary base pairs
  2. Phosphodiester bonds form;
  3. By (action of) RNA polymerase;
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29
Q

Give the two types of molecules from which a ribosome is made (1)

A
  • one of of RNA / ribonucleic acid / nucleotide/nucleic acid/rRNA / ribosomal RNA / ribosomal ribonucleic acid
    and
  • one of protein(s) / polypeptide(s) / amino acid(s) / peptide(s) / ribosomal protein

rRNA + protein

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30
Q

Define mutation (1)

A
  • ( random ) Change in the base/nucleotide (sequence of chromosomes/DNA);
  • results in the formation of new allele
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31
Q

Explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual. (4)

A

no effect : ( any 2 of )
- Genetic code is degenerate (so amino acid sequence may not change);
- Mutation is in an intron (so amino acid sequence may not change);
- Does change amino acid but no effect on tertiary structure;
- (New allele) is recessive so does not influence phenotype;
positive effect :
- May result in increased reproductive success OR survival
- Results in change in polypeptide that positively changes its properties

degenerate : amino acids have more than one triplet/codon.

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32
Q

what is a substitution mutation?

A
  • nucleotide in DNA sequence is replaced by another
  • likely no change in the amino acid sequence
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33
Q

what is a deletion mutation?

A
  • nucleotide is lost in the DNA sequence
  • leads to a frame shift causing entire amino acid sequence to differ
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34
Q

Define mutagenic agent (2)

A
  • A factor that) increases (the rate of) mutations;
  • e.g. X rays , UV light , Gamma rays etc
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35
Q

What is a polyploidy chromosome mutation?

A
  • where an individual has three of more sets of chromosmes instead of two
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36
Q

Describe chromosome non-disjunction

A
  • occurs when chromosomes fail to separate during meiosis
  • gametes may end up with one extra copy of a particular chromosome or no copies

e.g. DOWN’S SYNDROME

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37
Q

Genetic variation within a species is increased during meiosis by crossing over and the independent segregation of homologous chromosomes. Apart from mutation, explain one other way genetic variation within a species is increased. (2)

A
  1. Random fusion of gametes
    OR
    - random fertilisation
  2. (Produces) new allele combinations
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38
Q

If most of the mitochondria in a cell are faulty, this prevents many important enzyme catalysed reactions taking place or slows them down.
Suggest and explain one reason why (2)

A
  • not enough/ little ATP produced
  • ATP provides energy for enzyme reactions
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39
Q

What is meiosis?

A
  • a form of cell division that produces four genetically different haploid cells known as gametes ( sex cells)
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40
Q

Give 4 differences between mitosis and meiosis. (4)

A
  • One division, two divisions in meiosis;
  • (Daughter) cells genetically identical, daughter cells genetically different in
    meiosis;
  • Two cells produced, (usually) four cells produced in meiosis;
  • Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
  • Separation of homologous chromosomes only in meiosis;
  • Crossing over only in meiosis;
  • Independent segregation only in meiosis;

Mitosis given first - then meiosis

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41
Q

Give difference between haploid and diploid (2)

A
  • Haploid =single set of chromosomes, denoted as “n”. In humans, the haploid number of chromosomes is 23. GAMETES
  • Diploid = having two sets of chromosomes, denoted as “2n”. In humans, the diploid number of chromosomes is 46. SOMATIC CELLS
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42
Q

Give the stages in Meiosis I

A
  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I

- same as mitosis except with crossing over

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43
Q

What is a bivalent?

A
  • a pair of homologous chromosomes that are joined together
44
Q

Name the two sources of genetic diversity in meisois (2)

A
  • crossing over
  • independent assortment
45
Q

Describe Prophase I

A
  • DNA condenses into visible chromosomes
  • Crossing over may occur at chiasma
  • Centrioles migrate to opposite poles , spindle forms, nuclear envelope breaks

  • Chromosomes consist of two sister chromatids joined by a centromere
46
Q

Describe the process of crossing over and explain how it increases genetic diversity. (4)

A
  • Homologous pairs of chromosomes come together + form a bivalent;
  • Chiasma(ta) form;
  • alleles are exchanged between non-sister chromatids
  • Recombination occurs producing new combinations of alleles;

happens during prophase

47
Q

Describe random assortment

also known as independent segregation

A
  • occurs during metaphase I of meiosis
  • Paired homologous chromosomes align randomly at the equator of the cell
  • leading to random distribution of chromosomes into daughter cells
48
Q

What happens during metaphase I?

A
  • The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres
49
Q

What happens during Anaphase I?

A

the bivalents separate and move to opposite ends of the cell

50
Q

What happens during telophase I?

A
  • spindle fibers start to break
  • Nuclear envelopes form, nucleoli reform
  • cytokinesis occurs after ( cell divides )
51
Q

Describe the result of meiosis II.

meiosis II is the same as meiosis I just with half the number of chromosomes and chromatids.

A
  • production of four haploid cells, each containing half the number of chromosomes compared to the original parent cell.
52
Q

Explain how the chromosome number is halved during meiosis.

A
  • Homologous chromosomes (pair);
  • One of each (pair) goes to each (daughter) cell / to opposite poles;
53
Q

Define population

A
  • all the organisims of a particular species that live in the same place
54
Q

Define genetic diversity.

A
  • Differences in DNA / differences in base sequence of DNA

enables natural selection to occur

55
Q

Name 4 processes that cause allele changes

A
  • natural selection
  • founder effect
  • genetic drift
  • bottleneck effect
56
Q

what is a genetic bottleneck and its impact

A
  • an event that causes a big reduction in a population
  • reduces genetic diversity as it reduces the number of alleles in the gene pool
57
Q

Define natural selection

A
  • an increase in the number of beneficial alleles in a population due to a selection pressure.
  • Selection pressures increase the chance of individuals with a specific phenotype surviving and reproducing over others
58
Q

Describe the process of natural selection

A
  • random gene mutations can result in new alleles of a gene
  • mutated allele is beneficial and makes organism well suited for the environment ( has a selective advantage)
  • more likely to surivie and have increased reproductive success
  • advantageous allele is inherited by members of the next generation (offspring)
  • over many generations, alle increases in frequency in the population
59
Q

benefit of genetic diversity

A
  • A population with a large gene pool or high genetic diversity has a strong ability to adapt to change
60
Q

what is the founder effect and its impact on genetic diversity

A
  • when only a small number of individuals from a large parent population start a new population
  • thus there are only a small number of alleles in their initial gene pool
61
Q

what is genetic drift

A
  • gradual change in allele frequencies in a small population due to chance but not natural selection
62
Q

Name three examples of selection pressures

A

Predation, competition and disease

63
Q

What are the 3 types of adaptations?

describe them

A

Behavioural: changes to action to increase survival e.g. hibernation
Physiological: changes to bodily processes e.g. venom production
Anatomical: changes to body stucture e.g. thick layer of blubber

64
Q

Name the 2 types of selection

A

Stabilising
Directional

65
Q

Describe stabilising selection

A
  • selects against the extreme phenotypes (high and low birth weights) and selects for the intermediate phenotypes (medium birth weights)
  • the middle range are more likely to survive and reproduce

search up graph:

66
Q

Give and describe an example of stabilising selection

A
  • human birth weights
  • Very-low and very-high birth weights are selected against as they are less likely to survive
  • leading to the maintenance of the intermediate birth weights

image : https://cdn.savemyexams.com/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Stabilising-selection-on-birth-weight.png

67
Q

Describe directional selection?

A
  • the extreme phenotype is favoured
  • occurs when environmental conditions change
  • individuals with phenotypes suited to the new conditions are favoured

image [https://cdn.savemyexams.com/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Directional-selection-antibiotic-resistance.png]

68
Q

Give and describe an example of directional selection.

A
  • antibiotic resistance
  • antibioits is a selection pressure.
  • Mutation occurs in bacteria that is resistant to antibiotic
  • more likely to survive and reproduce
  • over generations, this allele is favoured and leads to an increase in the frequency of the beneficial allele
69
Q

define species

A
  • a group of organisms that can interbreed to produce fertile offspring.
70
Q

Define allopatric speciation .

A
  • speciation that occurs when populations of the same species become geographically isolated from each other.
  • thorugh geographic barriers such as mountains, rivers
  • Isolated populations evolve independently, accumulating genetic differences over time.

Example: Galápagos finches

71
Q

Describe sympatric speciation.

A
  • Speciation that occurs within the same geographic area where the parent species is found.
  • ## often due to factors like polyploidy, habitat differentiation, or behavioral changes.

[https://studymind.co.uk/notes/mechanism-of-natural-selection/?catid=19]

72
Q

define speciation

A

formation of a new species e.g. through allopatric or sympatric speciaion

73
Q

Compare and contrast allopatric and sympatric speciation (3)

A
  • Allopatric speciation is slower than sympatric speciation
  • Allopatric speciation takes place through geographical isolation whereas sympatric speciation does not
  • Allopatric speciation occurs through natural selection whereas sympatric speciation occurs through polyploidy or beahvioural differences
74
Q

What is courtship behaviour?

A
  • behaviours such as visual , chemical or auditory stimuli that result in mating and reproduction.
75
Q

what are the advantages of courtship behaviour?

A
  • indivudals can recognise sexually mature members of their own speices of opposite sex
  • syncronhise mating
  • form a pair bond and sucessfully breed
76
Q

Give three ways in which courtship behaviour increases the probability of successful mating (3)

A
  1. Recognise / identify / attract same species;
  2. Stimulates / synchronises mating / production / release of gametes;
  3. Recognition / attraction of mate / opposite sex;
77
Q

Define classification

A
  • the process of arranging organisms into groups
78
Q

what is taxonomy?

A
  • practice of biological classification
79
Q

Name the 8 groups in the classification hierachy

largest to smallest

A

domain-kingdom-phylum-class-order-family-genus-species

each group is called a taxon

80
Q

Name the three domains that organisms are first sorted into

A

Eukarya
Bacteria
Archaea : prokaryotes that thrive in extreme environments

81
Q

what is the binomial naming system?

A
  • The first name is the genus and
  • The second name is the species
  • The names are usually Latin

Homo sapiens

Homo - genus / sapiens = species

82
Q

How are binomial names handwritten?

A
  • first letter of generic name is capitalised , with rest being lowercased
  • whole name must be underlined
83
Q

What is phylogenetic classification?

A
  • process of arranging organismis into groups based on their evolutionary origins and relationships
84
Q

Name the techniques that are useful for clarifying evolutionary relationships

A
  • Genome sequencing
  • Comparing amino acid sequence
  • Immunological comparisons
85
Q

Explain how genome sequencing is useful for clarifying evolutionary relationships

A
  • Advances in genome sequencing allows comparison of dna base seuqneces
  • Closely related species will have a higher percentage of similarity in their DNA base order.
  • more different - less similar dna base sequnece as mutations build up over time
86
Q

Explain how comparing amino acid sequences helps to clarify evolutionary relationships

A
  • The sequence of amino acids in a protein is coded for by the base sequence in DNA.
  • Related organisms have similar DNA sequences, and so similar amino acid sequences
  • The more similar the sequence of cytochrome C, the more closely related they are
87
Q

How can immunological comparisons help to clarify evolutionary relationships?

A
  • An organism’s antibodies can be isolated and mixed with another organism’s proteins to see how many antigen-antibody complexes are formed.
  • The more complexes that form, the more closely related the two organisms are.
  • as similar tertirary structure and amino acid sequences
88
Q

Explain hierachical classification

A
  • groups within groups
  • no overlap within groups

dog cant be a human and a dog within species
species is part of a certain domain

89
Q

Define biodiversity

A
  • variety of living organisims
  • can be measured through species diversity , ecosystem and genetic diversity
90
Q

Define community.

A
  • all the different species that live in one area and interact with one another
91
Q

define species richness.

give a weakness

A
  • number of species within a community
  • can be misleadgin g, as it does not take into account the individuals of each species.
92
Q

define index of diversity.

A
  • describes the relationship between the number of species in a community and the number of individuals in each species.
93
Q

How do you calculate index of diversity?

A

d = N ( N-1) / {n(n-1)
- the larger the number obtained , the higher the level of diversity.

N= total number of organisims of all species
n= total number of organisms each species
{ - sum of

94
Q

what impact does farming have on species diversity?

A
  • decreases species richness
  • farmland is typically used for one species
  • use of pesticides/ herbicides
95
Q

what impact does farming have on genetic diversity?

A
  • decreases
  • farmers select for certain characteristics , which reduce number of different alleles in the population.
96
Q

How can biodiversity be increased in areas of agriculture?

A
  • use hedgerows instead of fences
  • grow different crops around in the same area, or rotate crops around after a season
  • limit use of pestricides and herbicides.
97
Q

Name four ways we can compare genetic diversity between organismis.

A
  1. frequency of observale characteristics
  2. base sequence of DNA
  3. base sequence of mRNA
  4. Amino Acid Sequence
98
Q

How is measurable and observing characteristcs used for dtermineg genetic diersity?

give limitation

A
  • measurable : included number of legs , seeds , peetals , leaf indentations
  • observable : colour , patters on fur etc , habitat
  • not precise enough if only one characteristic is looked at
  • simply inferring DNA differences throuch characteristcics of an organism is not reliable as could have external influences i.e environment
99
Q

How is DNA sequencing used to determine genetic diversity?

A
  • DNA is extracted from the nuclei of cells taken from an orgaism through skin samples or fossils.
  • base sequences is obtained and compared to that of other organisms to determine evolutionary relationships.
  • the more similarities in DNA base sequences , the more closely related members of diff species are
100
Q

How is mRNA sequencing used to determine genetic diversity?

A
  • often easier to isiolate from cells than DNA.
  • mRNA can be used as a template to produce CDNA ( complemetary DNA.

icl dk what this is on about

lmao links to topic 8

101
Q

How is amino acid sequencing analysis used to determine genetic diversity?

give limitation

A
  • sequence of amino acids of the same protein can be compared ( must be found in all species being compared to e.g haemoglobin)
  • evolves slower than DNA so may have same sequece but not as closely related as entailed.
102
Q

what is meant by interspecific and intraspecific variation?

A
  • interspecific : differences between indiviuals of different species
  • intraspecific: differences between inndividuals of the same species
103
Q

what is sampling?

A
  • a method of investigating the abundance and distribution of species and populations.
  • can be random or systematic
104
Q

Give key differece betwee random and systematic sampling.

A
  • in random sampling, positions of the sampling points are completely random or due to chance.
  • this method is benefical because it means there will be no bias by the researcher.
  • in systematic sampling , the positions of the sampling points are chosen by the person carrying out. There is a possibility of bias.
  • when a sampling area is reasonably uniform, or has no clear pattern to the way the species are distributed then random sampling is favoured.
105
Q

How are quadrats used in random sampling??

A
  • create a grid for your sample area.
  • use a random number generator to choose a set of coordiantes where the quadrat will be placed to remove bias
  • calculate population density by counting number of indidvuals in each quadrat.
  • use a running mean to get a representative sample.
  • repeat until required sample size is reached
106
Q

limitations of qudrats

A
  • can only be used for sessile and immobile species ( plants and slowmoving animals)
  • see save my exams