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A-Level Biology AQA > 4. Genetic Information, Variation, and Relationships between Organisms > Flashcards

4. Genetic Information, Variation, and Relationships between Organisms Flashcards

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1
Q

what is a gene?

A

a short section of DNA that codes for a polypeptide or functional RNA

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2
Q

what do genes that do not code for a polypeptide code for instead?

A

functional RNA

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3
Q

what is meant by the term ‘code’?

A

the specific sequence of bases that codes for each amino acid, that forms the order of amino acids on the polypeptide chain

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4
Q

what is each amino acid coded for by?

A

a sequence of three bases in a gene called a triplet

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5
Q

what is a triplet of bases referred to as?

A

a codon

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6
Q

define the term proteome

A

the full range of proteins a cell is able to produce

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7
Q

define the term genome

A

the complete set of genes within the cell

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8
Q

what is a locus?

A

the locus is the location of a particular gene on a chromosome

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9
Q

what is an allele?

A

an allele is one of a number of different alternatives for a gene (different forms of the same gene)

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10
Q

how do alleles differ?

A

alleles differ in their base sequences

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11
Q

what is a chromosome?

A

chromosomes are where dna is stored

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12
Q

what do chromosomes consist of?

A

tightly coiled dna

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13
Q

how many chromosomes do humans have?

A

46 chromosomes, 23 pairs

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14
Q

how are homologous chromosomes the same? how do they differ?

A

homologous chromosomes are the same size and have the same genes
homologous chromosomes may have different alleles

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15
Q

what is an image that displays all the 23 pairs of chromosomes for humans called?

A

karyotype

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16
Q

what are the proteins that dna tightly wraps itelf around called?

A

histones

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17
Q

why does dna tightly wrap around histone proteins?

A

to enable it to fit into the chromosomes and not get tangled

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18
Q

what is the complex of a dna strand wrapped around a histone called?

A

a chromosome (made from many nucleosomes)

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19
Q

what are introns?

A

dna that does not code for amino acids and therefore polypeptides

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20
Q

what are exons

A

genes that do code for amino acids and therefore polypeptides

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21
Q

when are introns removed and why?

A

introns are removed during protein synthesis by mRNA molecules so they dont affect the amino acid order

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22
Q

state the differences between prokaryotic and eukaryotic dna

A
  • eukaryotic dna contains introns whereas prokaryotic dna does not
  • eukaryotic dna is bound to histones whereas prokaryotic dna is not
  • eukaryotic dna is enclosed within a nucleus whereas prokaryotic dna is not
  • eukaryotic dna is longer and linear whereas prokaryotic dna is shorter and circular
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23
Q

state the similarities between prokaryotic and eukaryotic dna

A
  • both kinds contain exons
  • both are stored within chromosomes
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24
Q

why is there dna found in organelles such as mitochondria and chloroplasts?

A

because dna codes for the amino acids that form the proteins (such as enzymes) needed for the essential reactions within these organelles to occur, such as aerobic respiration in mitochondria and photosynthesis in chloroplasts

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25
Q

are there introns in prokaryotic dna?

A

no

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26
Q

what is the start codon?

A

the triplet of bases at the start of a gene

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27
Q

how many amino acids can the genetic code code for?

A

20

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28
Q

how many dna bases are there in total?

A

four - adenine, guanine, cytosine and thymine

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29
Q

how can it be proven mathematically that only three of the four dna bases are needed to code for the 20 amino acids in the genetic code?

A

4^n
4^1 = 4 which isnt enough amino acids
4^2 = 16 which also isnt enough
4^3 = 64 which is more than enough to code for 30 amino acids

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30
Q

why is the genetic code described as being degenerate?

define what the term degenerate means

A

as three dna bases can code for a total of 64 amino acids (4^3=64) which is more than enough for the 20 amino acids in the genetic code

degenerate means that more than one triplet of bases can code for the same amino acid

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31
Q

what is an advantage of the genetic code being degenerate?

A

if a point mutation occurs, even though the triplet of bases will be different, they may still code for the same amino acid, and therefore the mutation will have no overall effect on the polypeptide produced

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32
Q

define what is meant by ‘the genetic code is universal’

A

the same triplet of bases codes for the same amino acids in all organisms

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33
Q

what is an advantage of the genetic code being universal?

A

enables genetic engineering to occur

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34
Q

define what is meant by ‘the genetic code is non-overlapping’

A

each base in a gene is only part of one triplet of bases that codes for one amino acid - each triplet of bases is read separatley as one discrete unit

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35
Q

what is an advantage of the genetic code being non-overlapping?

A

if a point mutation occurs, it will only affect one codon, and therefore only one amino acid

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36
Q

briefly describe what happens during transcription?

A

the genetic code is copied from a section of dna (a gene) onto mrna

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37
Q

why is the genetic code copied onto mrna during protein synthesis?

A
  • because mrna is much shorter than dna so is able to carry the genetic code to the ribosome in the cytoplasm - enabling the protein to be made
  • dna is essentially too big to leave the nucleus through the nuclear pores, and also enzymes in the cytoplasm could damage the dna and genetic code, which is why mrna is sent instead
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38
Q

recall the steps for the process of transcription

A
  • rna polymerase attaches to the dna helix at the start of a gene
  • dna helicase causes the dna helix to unwind and break the hydrogen bonds between complementary bases, leaving them exposed
  • only one dna strand acts as a template
  • rna polymerase lines up free rna nucleotides on the template strand. the rna bases are attracted to their complementary dna base on the template strand, and the bases join together by complementary base pairing (adenine with uracil, cytosine with guanine)
  • hydrogen bonds between complementary bases reform
  • rna polymerase joins adjacent rna nucleotides using phosphodiester bonds
  • pre-mrna is spliced to form mature mrna (introns are removed)
  • mrna moves out of the nucleus through the nuclear pores and attaches to a ribosome in the cytoplasm
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39
Q

recall the steps for the process of translation

A
  • mrna attaches to the ribosome at the start codon
  • a trna molecule carries a specific amino acids to the mrna strand, which requires atp
  • the trna molecule has an anticodon that is complementary to the mrna codon
  • the complimentary anticodons attaches to the codon on mrna by specific base pairing
  • a second trna molecule attaches itself to the next codon in the same way
  • the two adjacent amino acids attached to the trna molecules are joined by a peptide bond, which requires atp
  • trna is released after amino acid joins the polypeptide
  • the ribosome moves along the mrna to complete the polypeptide
  • this process continues until the ribosome reaches the stop codon at the end of the mrna strand
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40
Q

how many trna molecules can fit on the ribosome at a time during translation?

A

two

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41
Q

why does the stop codon stop translation?

A

the stop codon stops translation as it does not code for an amino acid, so tRNA has no specific amino acid to bring to the mRNA strand, therefore the complimentary antocodon on tRNA cannot bind to the codon on mRNA, so the ribosome detaches and translation ends

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42
Q

explain why protein synthesis is an active process

A

energy is required to make the peptide bonds between adjacent amino acids

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43
Q

what happens to the polypeptide chain after translation?

A

it enters the golgi apparatus for modification and folding to become a protein

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44
Q

what does the rna nucleotide consist of?

A
  • ribose pentose sugar
  • phosphate group
  • nitrogenous base adenine, guanine, cytosine, and uracil
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45
Q

differences between rna and dna structure?

A
  • dna is longer
  • dna is double stranded whereas rna is not
  • dna contains thymine whereas rna contains uracil
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46
Q

what is the function of rna?

A

to copy and transfer the genetic code in the nucleus to the ribosomes

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47
Q

what is mrna?

A

messenger rna is a copy of a gene from dna made during transcription that carries the genetic code from the nucleus to the ribosomes

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48
Q

what is the shape of mrna?

A

linear

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49
Q

where is trna found?

A

transfer rna is only found in the cytoplasm

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50
Q

what is the function of trna?

A

to attach to one of the 20 amino acids and transfer it to the mrna strand on the ribosome

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51
Q

what is the shape of trna?

A

single stranded, but folded into a clover leaf shape, held in place by hydrogen bonds

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52
Q

what is rrna?

A

the type of rna that makes up the bulk of ribosomes

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53
Q

what is meiosis needed for?

A

sexual reproduction as it produces gametes

54
Q

what are gametes?

A

sex cells that join together during fertillisation to produce diploid zygotes

55
Q

how many chromosomes do normal body cells have?

A

a diploid number of chromosomes - 23 pairs = 46

56
Q

how many chromosomes do gametes have?

A

a haploid number of chromosomes

57
Q

define what is meant by the term diploid

A

when a cell contains two copies of each chromosome

58
Q

define what is meant by the term haploid

A

when a cell only contains one copy of each chromosome

59
Q

what happens before meiosis 1?

A

dna replicates so that there is two copies of each chromosome

60
Q

describe what happens during prophase 1 in meiosis

A

dna condenses to form double armed chromosomes, made from two sister chromatids joined at the centromere
- chromosomes arrange themselves into homologous pairs

61
Q

describe what happens during metaphase 1 in meiosis

A

the homologous pairs of chromosomes line up along the equator of the cell

62
Q

describe what happens during anaphase 1 in meiosis

A

homologous pairs of chromosomes are separated, halving the chromosome number

63
Q

describe what happens during telophase 1 and cytokinesis in meiosis

A

the chromosomes reach opposite poles of the cell and the cytoplasm divides, producing genetically different cells

64
Q

describe what happens during meiosis 2

A
  • chromosomes line up along the equator of the cell
  • spindles contract, splitting the centromere, so sister chromatids are pulled to opposite poles of the cell
  • chromatids reach opposite poles of the cell and cytoplasm divides, producing four genetically different haploid daughter cells
65
Q

what are the two mechanisms in meiosis that introduce variation?

A

independent segregation
crossing over

66
Q

describe and explain how independent segregation introduces genetic variation

A
  • in meiosis 1, homologous pairs of chromosomes line up opposite eachother at the equator of the cell
  • it is completley random which side of the equator the maternal and paternal chromosomes will be on
  • when they are separated, one of each pair ends up in a daughter cell
  • this shuffling leads to different combinations of chromosomes, and so different combinations of alleles in each daughter cell
  • this creates a large number of possible combinations of chromosomes in the daughter cells produced
67
Q

describe what happens during crossing over and define what is meant by a chiasmata

A
  • in meiosis 1, homologous pairs of chromosomes line up opposite eachother at the equator
  • pairs of non-sister chromatids can become twisted around eachother
  • a chiasmata forms as a result, which is the point of contact between two non-sister chromatids belonging to homologous chromosomes
68
Q

describe the process of crossing over and explain how it introduces genetic variation

A

1.non sister chromatids belonging to homologous pairs of chromosomes associate

2.chiasmata forms, which puts tension on the chromatids, causing the segments to break off

3.equal lengths of non-sister chromatid segments are exchanged

4.producing new combinations of alleles

69
Q

explain how random segregation also introduces genetic variation

A
  • it is random which egg and sperm will fuse together in fertillisation
  • (26n)^2 possible combinations of chromosomes when random segregation is considered
70
Q

state the equation that can be used to figure out the number of possible combinations of chromosomes in daughter cells

A

2^n
where n is the number of homologous pairs

71
Q

state 4 differences between mitosis and meiosis

A

mitosis has one nuclear division whereas meiosis has two

mitosis produces diploid cells whereas meiosis produces haploid ones

mitosis produces genetically identical cells whereas meiosis produces genetically different ones

mitosis produces two daughter cells whereas meiosis produces four daughter cells

72
Q

how to tell where meiosis is occuring in an unfamiliar cycle?

A
  • all you need to remember is that meiosis involves a diploid parent cell (2n) dividing to become a haploid cell (n)
  • so remember the section meiosis is occuring in is where the diagram goes from 2n to n!
73
Q

what is a chromosome mutation?

A

a change in the number of chromosomes

74
Q

how do chromosome mutations occur? define this process

A

chromosome mutations occur by non-disjunction
- non disjunction is when chromosomes in meiosis 1 and chromatids in meiosis 2 do not split equally during anaphase, meaning the resulting gamete will not have the correct number of chromosomes

75
Q

what do chromosome mutations lead to?

A

inherited conditions such as downs syndrome

76
Q

what are gene mutations?

A

gene mutations are changes to the dna base sequence of chromosomes

77
Q

how do gene mutations occur?

A

gene mutations occur spontaneoulsy during dna replication

78
Q

what are the three types of gene mutation?

A

substitution mutations
deletion mutations
insertion mutations

79
Q

what is a mutagenic agent?

A

a mutagenic agent increases the rate of mutations

80
Q

give four examples of mutagenic agents

A

ultraviolet radiation
ionising radiation
some types of chemicals and viruses

81
Q

describe what happens during a substitution mutation

A

a substitution mutation is when one or more of the bases are replaced for another during dna replication. only the codon with the mutation is affected

82
Q

describe what happens during a deletion mutation

A

a deletion mutation is when one base is left out (deleted) during dna replication. this causes a frame shift, which is when all the codons after the mutation are affected.

83
Q

describe what happens during an insertion mutation

A

an insertion mutation is when an extra base is added during dna replication. this results in a frame shift, which is when all the codons after the mutation are affected.

84
Q

how may a gene mutation change the protein produced and its function?

A
  • the mutation may cause the sequence of the amino acids to change
  • this would result in the hydrogen/ionic/disulphide bonds between the R groups changing, causing the tertiary structure of the protein to change
85
Q

state and explain 4 reasons why a gene mutation may not affect the protein produced and its function

A
  • if, due to the degenerate nature of the genetic code, the mutation codes for the same amino acid
  • if the mutation occurs in an intron
  • if the mutation is in a recessive allele
  • if in an enzyme, the mutation occurs away from the active site, so the active site remains the same shape.
86
Q

define what is meant by genetic diversity

A

the number of different alleles of genes in a population

87
Q

what is meant by a gene pool?

A

the sum of all the alleles in a population

88
Q

what is the only time natural selection can occur?

A

when there is genetic diversity within a population

89
Q

state two ways in which genetic diversity can be increased

A

mutations and migration

90
Q

state four ways in which genetic diversity can be decreased?

A

genetic bottlenecks
founder effects
inbreeding
decreases in population size

91
Q

what does natural selection lead to?

A

evolution in populations
species becoming better adapted to their environment

92
Q

define what is meant by evolution

A

the change in allele frequency over many generations in a population

93
Q

describe the process of natural selection

A
  • new alleles for a gene are created by random mutations
  • if the new alleles increase the chance of the organism’s survival in that environment (have a selective advantage), organisms with this allele are more likley to survive and reproduce
  • this reproduction passes on the advantageous allele to the next generation
  • as a result, over many generations, the new allele increases in frequency within the population
94
Q

name the three types of adaptation

A

behavioural
physiological
anatomical

95
Q

what is a behavioural adaptation

A

ways an organism acts that increases its chances of survival and reproduction

96
Q

what is a physiological adaptation

A

processes inside an organisms body that increase its chances of survival. eg when bears hibernate over winter, they lower their metabolism, which conserves energy so they dont need to look for food

97
Q

what is an anatomical adaptation

A

structural features of an organisms body that increase its chances of survival

98
Q

describe what is meant by ‘genetic bottleneck’

A

a genetic bottleneck is a random event that causes a big reduction in a population. this means that a large number of the population die before reproducing. this reduces the number of different alleles in the gene pool.

99
Q

describe what is meant by a founder effect

A

a founder effect occurs when few organisms from a larger original population start a new colony. the new colonys population only has a small number of different alleles in the inital gene pool

100
Q

state the two types of selection

A

directional
stabilising

101
Q

what is directional selection?

A

when the extreme trait has the selective advantage, and occurs when there is an environmental change.
this means individuals with an allele for an extreme trait are more likely to survive and reproduce

102
Q

explain how antibiotic resistance in bacteria shows directional selection

A
  • some bacteria in the population have alleles that make them resistant to antibiotics
  • when the population is exposed to the antibiotic, those without the resistance allele will die
  • the resistant bacteria will survive and reproduce, passing on the resistance allele to their offspring (the next generation)
  • after some time, most organisms in the population will carry the antibiotic resistance allele
103
Q

what is stabilising selection?

what is disruptive selection?

A

when the modal trait has the selective advantage, and occurs when there is no environmental change
the standard deviation decreases as there is less genetic variety, as the modal trait remains the same and individuals with the extreme traits decrease

when individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce. this occurs when the environment favours more than one phenotype

104
Q

explain how human birthweight shows stabilising selection

A
  • humans have a range of birthweights
  • very small babies are less likley to survive as they find it difficult to maintain body temperature
  • giving birth to large babies can be difficult, so large babies are less likely to survive too
  • conditions are most favourable to medium sized babies, so selection tends to shit to the middle of the range (the modal trait)
105
Q

what is a selection pressure?

A

an external factor that influences the survival and reproductive success of an individual

106
Q

what is taxonomy?

A

the science of classification

107
Q

what is phylogeny?

A

the study of the evolutionary history of groups of organisms, and tells us how closley related the species are

108
Q

define what is meant by the term ‘hierachy’

A

when smaller groups are placed within larger groups, with no overlap between groups

109
Q

define what is meant by the term ‘species’

A

similar organisms that can interbreed to produce fertile offspring

110
Q

how does the binomial system name organsims?

A

Genus species (itallics)
has to be underlined if it is written by hand
genus is always capitallised

111
Q

what are the advantages of using a binomial system to classify organisms?

A
  1. its a universal method
  2. it helps to avoid the confusion that comes with using common names
  3. it helps to see how closley related species are
112
Q

what are the three large domains organisms are sorted into?

A

eukaryota, bacteria and archea

113
Q

what is the accronym used to remember the classification system?

recall the 8 different taxa in the classification system

A

dear king phillip came over for good spaghetti

domain
kingdom
phylum
class
order
family
genus
species

114
Q

what are the problems with trying to classify organisms based on appearance alone?

A
  • they live in similar environments and are exposed to similar selection pressures
  • they have similar alleles that provide similar selective advantages
115
Q

state and explain the four modern accurate classification methods

A
  • dna sequences - the more similar the sequence, the more closley related the organisms are
  • mrna sequences - the more similar the sequence, the more closley related the organims are
  • amino acid sequence - the more similar the sequence, the more closley related the organisms are
  • immunology - similar antigens in organisms will bind to the same antibodies. the larger the precipitate band, the more closley related the organisms are.
116
Q

What is the importance of courtship behaviour?

A

Courtship behaviour is essential for successful mating and species recognition.

117
Q

What are courtship rituals?

A

Courtship rituals are a sequence of actions unique to each species, used by animals to identify members of their own species for reproduction.

118
Q

Who typically performs courtship rituals?

A

males

119
Q

What are 5 examples of courtship behaviours?

A

Courtship behaviours can include dancing, singing, release of pheromones, fighting, and colourful feather displays

120
Q

Why is courtship important for reproduction?

A

Courtship ensures successful reproduction by enabling individuals to recognise members of their own species of the opposite sex and synchronising mating behaviour.

121
Q

What does the similarity of courtship sequences between different species indicate?

A

The more similar the courtship sequence is between different species, the more closely related the species are, as courtship rituals are genetically determined, so if the rituals are similar, then the base sequence of dna is also similar

121
Q

What are the three measures of biodiversity?

A

species diversity, genetic diversity, and ecosystem diversity.

122
Q

What is species diversity?

A

Species diversity is the number of different individuals within each species in a community.

123
Q

What is genetic diversity?

A

Genetic diversity is the variety of genes amongst all the individuals in a population of one species.

124
Q

What is ecosystem diversity?

A

Ecosystem diversity is the range of different habitats.

125
Q

What is species richness?

A

Species richness is the number of different species in a community at a particular time.

126
Q

How is biodiversity affected by human activity?

A

Biodiversity is reduced by human activity such as farming techniques.

127
Q

What are some common farming practices that reduce biodiversity?

A

Common farming practices that reduce biodiversity include destruction of hedgerows, selective breeding, pesticides and herbicides, monocultures, overgrazing, filling in ponds, and draining wetlands.

128
Q

What does the index of diversity describe?

A

The index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.

129
Q

How is the index of diversity calculated?

A

D = N(N-1) / Σn(n-1)

N is the total number of organisms of all species, and n is the total number of organisms in each species.

A-Level Biology AQA (7 decks)

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