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A-Level Biology > Unit 4 - Genetic Info, Variation & Relationships b/w Organisms > Flashcards

Unit 4 - Genetic Info, Variation & Relationships b/w Organisms Flashcards

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1
Q

define gene

A

sequence of DNA bases that code for a polypeptide or for a functional RNA (inc. rRNA & tRNA)

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2
Q

define locus

A

fixed position on a chromosome that a gene occupies

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3
Q

define allele

A

different versions of a gene
different alleles have slightly different nucleotide sequences but occupy the same locus on the chromosome

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4
Q

how are chromosomes arranged?

A

homologous pairs
one inherited from the father & one inherited from the mother

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5
Q

eukaryotic DNA vs prokaryotic DNA

A

eukaryotic vs prokaryotic
linear (formed in chromosomes) vs circular
in nucleus vs in cytoplasm
no plasmids vs plasmids present
introns present vs no introns present
longer & more genes vs shorter & fewer genes
both are a double-stranded helix structure

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6
Q

how is DNA packaged in eukaryotes?

A

DNA double helix
DNA wraps around/associates with histones proteins
DNA-histone complex is coiled
coils fold to form loops
loops coil & pack together to form a chromosome (visible under light microscope)

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7
Q

what is the structure of a chromosome?

A

homologous chromosomes have same genes at the same specific loci but may have different alleles (paternal & maternal chromosomes)
duplicated chromosome - sister chromatids joined at the centromere

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8
Q

describe karyotype

A

picture of all the chromosomes from a single diploid cell
homologous pairs can be identified due to distinctive banding after staining
sex chromosomes displayed to one side
all other chromosomes are called autosomes

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9
Q

what sex chromosomes correspond to each gender?

A

xy - male
xx - female

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10
Q

define genome

A

complete set of genes in a cell

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11
Q

define proteome

A

full range of proteins that a cell can produce
or coded for by the cell’s DNA

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12
Q

what are the features of genetic code?

A

triplet code
degenerate
non-overlapping
universal

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13
Q

describe triplet code

A

a sequence of 3 bases (codon) codes for a specific amino acid

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14
Q

describe degenerate code

A

some amino acids are coded for by more than one codon
3 codons (stop codons) do not code for any amino acid & are used to mark the end of a polypeptide chain
the start of the sequence is always the same codon

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15
Q

describe non-overlapping code

A

each base in the sequence is only read once
code is always read in one direction along the DNA strand

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16
Q

describe universal code

A

DNA is the same in all organisms
same triplet code for same amino acids

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17
Q

why might mutations in nucleotide sequence of a gene not cause a change in structure of polypeptide?

A

triplets code for the same aa
mutation in introns/non-coding region

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18
Q

describe messenger RNA

A

function: transfers DNA code from nucleus to cytoplasm & determines the sequence of aas during protein synthesis
complementary to DNA code
small enough to leave nucleus via nuclear pores
associates with ribosomes in cytoplasm
easily broken down & only exists when needed to make a protein
sequence of nucleotides in mRNA = genetic code

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19
Q

describe the process of transcription

A

DNA helicase separates polynucleotides by breaking hydrogen bonds (b/w DNA bases)
the non-coding DNA strand acts as a template
free RNA nucleotides align by complementary base pairing
uracil base pairs with the adenine on DNA instead of thymine
RNA polymerase joins adjacent RNA nucleotides
phosphodiester bonds
in eukaryotes, pre-mRNA is spliced & introns removed to form mRNA

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20
Q

describe the process of splicing

A

introns (non-coding sections) are removed
remaining exons (coding sections) join together
splicing does not happen in prokaryotes

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21
Q

compare DNA replication & transcription

A

replication uses DNA polymerase to synthesise new DNA polynucleotides vs transcription uses RNA polymerase to synthesise new RNA polynucleotides

replication creates identical DNA molecules before cell division by mitosis vs transcription converts DNA into mRNA

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22
Q

describe tRNA

A

small, single-stranded molecule
clover shape with one end of the chain longer
the longer section is the amino acid binding site, which binds to a specific aa
each tRNA carries a different aa to the ribosome
each amino acid has a specific anticodon, which pairs with the complementary codon on the mRNA by H bonds

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23
Q

describe the process of translation

A

mRNA attaches to ribosomes (on RER)
ribosome moves to start codon
anticodons bind to complementary mRNA codons by hydrogen bonds
tRNA brings a specific amino acid
amino acids join by peptide bonds
with the use of ATP
tRNA is released after aa is joined to polypeptide
the ribosome moves along the mRNA to form the polypeptide

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24
Q

extra notes on translation

A

start: 2 mRNA codons are exposed to the ribosome at once
mRNA is used as a template to which tRNA attaches
hydrogen bonds are formed b/w the start codon & complementary tRNA anticodon
cycle:
an enzyme in the ribosome catalyses the condensation of a peptide bond b/w 2 aas (needs ATP)
end:
stop codon at the end of mRNA - 3 stop codons in the genetic code
no tRNA has an anticodon which is complementary to stop codon
polypeptide released from ribosome & forms its specific tertiary structure to enable it to perform its function

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25
Q

describe the role of ribosomes in translation

A

hold tRNA & mRNA together so tRNA anticodon can bind to complementary mRNA codon & correct aa can be added to polypeptide chain
ribosomes made up of rRNA & protein in nucleolus
have large & small subunits that attach to mRNA
ribosomes move along the mRNA

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26
Q

comparison of DNA, mRNA & tRNA

A

see table

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27
Q

describe the role of atp in the process of translation

A

releases energy
so aas join to tRNA & peptide bonds form b/w amino acids

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28
Q

how are gene mutations caused?

A

DNA replicational errors in interphase
substitution, addition or deletion of bases from the normal sequence
can happen naturally
chance of mutation increased by mutagenic agents e.g. ionising radiation/UV/x-rays or chemicals/tar

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29
Q

define mutagenic agent

A

a factor that increases the rate of gene mutations

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30
Q

most mutations have a negative/neutral impact on the fitness of an organism (selected against) but some are beneficial & selected for by natural selection

A

.

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31
Q

what are the types of base substitution mutations?

A

silent mutation
mis-sense mutation
non-sense mutation
all are single base substitutions

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32
Q

describe silent mutation

A

new codon codes for same amino acid
so has no effect on protein’s primary structure bc the code is degenerate
so no effect on secondary & tertiary structure
so protein function is not affected

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33
Q

describe mis-sense mutation

A

amino acid changes
primary structure different
this could change secondary/tertiary structure of the polypeptide
might be different H, ionic & disulfide bonds
so alters the specific 3d shape & function of the protein

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34
Q

describe non-sense mutation

A

changed the amino acid to a stop codon
premature translation of the mRNA section so normal protein sequence is not completed
shorter primary structure so different 2/3 structure
might be different H, ionic & disulfide bonds
different specific 3d shape
loss of function e.g. no ESCs/Ab-Ag complexes formed

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35
Q

describe frameshift mutation caused by deletion/addition base mutation

A

base has been deleted causing a shift to the left
addition of a base causes a shift to the right
causes frameshift, shifting the last base of each codon into the next one, to produce a different sequence after the mutation
different primary structure
effect on 2/3 structure of the polypeptide & affects the protein’s structure & function

nb addition/deletion of bases in multiples of 3 does not cause frameshift so is less detrimental to overall protein

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36
Q

what is the function of meiosis?

A

produces four daughter gamete cells each with 1/2 the number of chromosomes as the parent cell & all genetically varied

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37
Q

meiosis involves 2 nuclear divisions

A

one diploid cell in reproductive organ (ovary/testes) divides twice to produce 4 haploid daughter cells, which are all genetically different

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38
Q

why is meiosis important?

A

1- it halves the number of chromosomes (from diploid to haploid), which allows sexual reproduction, the fusion of 2 gametes, without chromosome number increasing

2- it causes genetic variation by new combination of alleles
allows natural selection so species can adapt to environmental changes

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39
Q

other than meiosis, what causes genetic variation?

A

random gene mutations –> change in DNA base sequence
creates new alleles

random fertilisation = fusion of gametes –> new combinations of maternal & paternal alleles

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40
Q

summary of meiosis diagram

A

see notes

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41
Q

how does meiosis result in genetic variation?

A

crossing over of homologous chromosomes
independent segregation of homologous chromosomes
which causes new allele combinations

random fertilisation of gametes

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42
Q

describe the process of crossing over

A

chromatids of each pair twist around each other
tension –> often equal portions of chromatids break off = exchange of alleles
broken portions recombine with chromatids of its homologous partner = recombination
there are new genetic combinations of maternal & paternal alleles
each gamete contains a unique combination of alleles on a given chromosome = genetic variation

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43
Q

describe independent segregation

A

homologous chromosomes pair up on the equator of the cell in metaphase 1
each pair can be positioned in 2 ways
the position of each pair is independent to the position of all other chromosome pairs

44
Q

what is the formula for # of possible gametes from independent segregation

A

2^# of homologous pairs

45
Q

define chromosome mutations

A

changes in structure or number of chromosomes

46
Q

why does non-disjunction happen?

A

1- homologous chromosomes fail to separate in meiosis 1

2- sister chromatids fail to separate in meiosis 2

47
Q

what is the effect of non-disjunction?

A

in both cases, gametes are formed with either 1 extra or 1 missing chromosome
e.g. Down’s syndrome, Turner’s syndrome

48
Q

define evolution

A

the changes in allele frequency & in characteristics that occur in a population of organisms over time

49
Q

define genetic diversity

A

total number of different alleles of genes (for all the genes) in a population
it’s a factor that enables natural selection

50
Q

define gene pool

A

all the different alleles present in a population
larger gene pool = higher genetic diversity
some alleles more frequent in the population than others = higher allele frequency

51
Q

define population

A

all individuals of the same species living in the same place & can interbreed

52
Q

what are the 4 main principles of how natural selection works?

A
  1. genetic variation exists in a population of organisms
  2. one or more selection pressures act on the population
  3. the form that is best adapted to withstand selection pressure are more likely to survive & reproduce
  4. changes in characteristics of a population (evolution) occur over many generations
53
Q

how does natural selection work?

A

random DNA mutations cause new alleles of a gene in some individuals, which cause genetic variation
selection pressure is acting on the population
individuals with ____ who are better adapted to their environment (selective advantage) are more likely to survive & reproduce, passing on the beneficial allele to their offspring
so the beneficial allele frequency increases over time
this repeats over many generations

54
Q

define selection pressure

A

change in the environment that favours one form of organism over another

55
Q

examples of selection pressures

A

competition
predation
disease
environmental factors: termperature, soil factors (e.g. pH, mineral content) (plants)

56
Q

what do organisms compete for?

A

animals: for food, water, territory & mates
plants: space, sunlight, water & mineral ions

57
Q

what causes extinction?

A

very strong selection pressures

58
Q

what are the 2 types of selection?

A

directional & stabilising

59
Q

describe normal distribution

A

bell-shaped curve that represents the frequency of a feature/characteristic in a population that shows continuous variation e.g. height

the characteristics are determined by many genes & environmental influences so can take a large range of intermediate values

most of the population are close to the mean value
mean = peak

60
Q

define standard deviation

A

measure of the spread of the data around the mean value

61
Q

describe directional selection

A

type of natural selection that favours individuals that vary in one direction away from the mean population
mean & normal distribution curve move in one direction

62
Q

example of directional selection

A

antibiotic resistance in bacteria
selection pressure = antibiotics
bacteria that are resistant to antibiotics have a selective advantage over non-resistant bacteria
so are more likely to survive & reproduce
passing on beneficial allele for antibiotic resistance to offspring, increasing the frequency of the beneficial allele over time

63
Q

describe stabilising selection

A

type of natural selection that favours the mean individuals
preserves characteristics of a population
tends to select against phenotypes at the extremes
mean stays the same but sd decreases

64
Q

example of stabilising selection

A

human birth weights

65
Q

how to answer natural selection 6 markers

A
  1. state variation occurs
  2. insert info from question
  3. variation due to random mutation –> new alleles
  4. selective advantage of new allele (insert info from question)
  5. more likely to survive & reproduce, passing on beneficial allele to offspring
  6. over time, increase in frequency of beneficial allele
66
Q

what are the 3 types of adaptations

A

anatomical - structural
physiological - biological processes
behavioural

67
Q

what is a species?

A

group of similar organisms that interbreed to form live, fertile offspring

individuals of the same species have very similar behaviour, appearance, anatomy, physiology, biochemistry & genetics

68
Q

what is courtship behaviour?

A

behaviour of the same species is more similar than the behaviour of different species
individuals can recognise their own species by the way they behave

69
Q

how does courtship behaviour ensure mating is successful & offspring have the best chance of surviving?

A

it enables individuals to:
1. recognise members of their species to produce fertile offspring

  1. identify a mate capable of breeding - sexually mature, receptive & fertile
  2. form a pair bond - possible life-long monogamous bond leads to successful mating & raising of offspring
70
Q

why is courtship behaviour important?

A

it maximises reproductive efficiency
it maintains reproductive isolation of a species
it allows females to pick the ‘fittest’ male

71
Q

what is classification?

A

the process of placing living things into groups

72
Q

(what are the reasons for classification?)

A

it is convenient as it makes the study of organisms more manageable
makes it easier to identify organisms
helps us to understand relationship b/w species
allows prediction of behaviour/characteristics of newly discovered species based on existing similar ones

73
Q

what is the binomial name for a species?

A

genus & species
capital letter for genus

74
Q

what are groups of organisms called, what kind of system is it & what are they based on?

A

taxa
hierarchical system
organisms’ similarities & differences

75
Q

what are the 2 features of a hierarchical system?

A
  1. smaller groups are found within larger groups
  2. there is no overlap b/w groups
76
Q

what is the order of taxa?

A

domain
kingdom
phylum
class
order
family
genus
species

77
Q

(what are the 3 domains & their features?)

A

eukarya:
eukaryotes
have membrane bound organelles (mbo)
80s ribosomes & 70s in mitochondria
no murein in CW if present
linear DNA enclosed in nucleus (w histones)

bacteria:
prokaryotes
no mbo
70s ribosomes only
murein CW
loop of DNA, no histones, no nucleus

archaea:
primitive prokaryotes, extremophiles
no mbo
70s ribosomes only
no murein in CW
loop of DNA w histones, no nucleus

78
Q

define phylogeny

A

classification based on evolutionary origin

79
Q

how do you interpret a phylogenetic tree?

A

top line = species exists present day
extinct if below the top line

intersection of line = species evolved from same common ancestor - now extinct

use comparative terms e.g. X is more closely related to Y because they share a more recent common ancestor

80
Q

what did Darwin’s theory of evolution suggest?

A

all living organisms share a common ancestor - ‘last universal common ancestor’

81
Q

define phylogenetics

A

study of evolutionary relationships b/w species

82
Q

what limited method can be used to compare species?

A

the frequency of measurable & observable characteristics

83
Q

instead, what technologies are used to compare similarities & differences b/w species & why?

A

amino acid sequences
mRNA sequences
DNA sequences
comparison of Ab-Ag associations = immunological technique
bc they are more accurate

84
Q

gene technology has caused a change in methods of investigating diversity…

A

measurable & observable characteristics replaced by direct investigation of DNA sequence

85
Q

how are amino acid sequences used to compare species?

A

comparison of amino acid sequences in protein show closeness of evolutionary relationships b/w different species
the more differences in an AA sequence, the more distant the relationship

86
Q

what is the limitation of using AA sequences/why is DNA sequencing better?

A

genetic code is degenerate so differences by silent substitution mutations in DNA sequence might not be shown in the AA sequence

random mutations happen over time so more differences = more time since the 2 species diverged from their common ancestor

87
Q

how are mRNA sequences used to compare species?

A

easier to isolate mRNA from cells than DNA bc it is in cytoplasm & there are multiple copies of the same mRNA
but
only coding regions (exons) are present in mRNA

88
Q

how are DNA sequences used to compare species?

A

best method
comparison of nucleotide sequence is more accurate than AA sequences
if there are many differences in DNA sequence of the same gene in 2 species, this shows the species are less closely related/evolved separately for a long time
to compare 2 different species, the same gene/protein must be used e.g. RNA polymerase of cytochrome c

89
Q

what is the method for the immunological technique of comparing species?

A
  1. serum of blood proteins is injected from human to rabbit
    Abs produced in rabbit’s blood attach to protein in human’s blood
  2. the rabbit’s blood is taken & Abs that are anti-human protein are extracted
  3. anti-human antibodies are added to blood samples from other species to see if they recognise proteins in different blood

the more similar the blood proteins to the original human blood, the greater the reaction so more precipitate of Ab-Ag complexes forms

90
Q

what do scientists use to get valid conclusions & why?

A

a number of sources & different methods
bc differing sources give differing results

91
Q

define biodiversity

A

the range, proportion and variety of genes, species & habitats within a particular area at a given time

92
Q

define species diversity

A

the number of different species & number of individuals in each species in a community

93
Q

define species richness

A

the number of different species in a community

94
Q

define genetic diversity

A

the number of different genes in a population (all individuals in 1 species)

95
Q

how can biodiversity be measured?

A

index of biodiversity measures species diversity - describe the relationship b/w the number of species & the number of individuals in each species
shows stability of ecosystem

96
Q

the greater the index of biodiversity (d),

A

the greater the biodiversity & stability of an ecosystem so the greater the chance of surviving environmental change e.g. climate change

97
Q

what is the formula for index of biodiversity?

A

d = N(N-1) / Σn(n-1)
N = total number of organisms of all species
n = total number of organisms of each species

98
Q

why is agriculture increasing & what is the general effect on biodiversity?

A

increasing population & increasing standard of living = increasing demand for cheap, good quality food
so increased demand on land
increasing demand for organic food = more land needed for same yield

this leads to loss of habitat bc land is used for farming
so loss of breeding areas

99
Q

what are the 4 pressures due to agriculture?

A

monoculture
pesticides
removal of hedgerows
fertilisers

100
Q

what is monoculture & its effect?

A

having a field of 1 crop replacing a species-rich area
which decreases gene pool & number of alleles so genetic diversity & biodiversity decrease

101
Q

what are the types of pesticides & what are their effect?

A

herbicides, insecticides, fungicides

can affect non-target species
toxic
can disrupt natural food chain
so biodiversity decreases

102
Q

what is the + effect of removing hedgerows?

A

increased space for crops = more crop yield & more money for farmers
removes competition with crops for resources

103
Q

why is there more species diversity in hedgerows?

A

they provide more habitats & niches
so there are more plant species
so an increased range of food
so increased diversity of species that eat the food

104
Q

what is the - effect of removing hedgerows?

A

reduced shelter for organisms
loss of habitats & niches
fewer plant species
so decreased range of food
so decreased species diversity & biodiversity

105
Q

how do hedgerows reduce money spent on pesticides?

A

increase number of predators of pests

106
Q

what is the effect of fertilisers? (+ & -)

A

+: nitrogen rich - to increase rate of AA production –> increased growth & yield

-: causes loss of rarer, slower growing species e.g. orchids bc they are outcompeted by faster growing crop
& eutrophication (U6th)

107
Q

what are the negative consequences of agriculture?

A

disruption of food chains
loss of natural predators
loss of species
reduced species richness
decrease in biodiversity

A-Level Biology (10 decks)

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