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A-Level Biology > Genetics, Biodiversity and Classification > Flashcards

Genetics, Biodiversity and Classification Flashcards

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1
Q

what is a gene?

A

a section of DNA that contains a code for making a polypeptide and functional RNA - the code is a specific sequence of bases

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2
Q

what is a locus?

A

location of a particular gene on a chromosome

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3
Q

what is an allele?

A

one of a number of alternative forms of a gene

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4
Q

what are homologous pairs?

A

chromosomes that have exactly the same genes, but might have different alleles and are exactly the same size

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5
Q

how is DNA stored in a eukaryote?

A
  • stored as chromosomes in nucleus
  • chromosomes in eukaryotic cells are linear in shape
  • to tightly coil DNA to fit in nucleus as chromosomes, DNA tightly wound around histones (a protein) to form nucleosomes
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6
Q

what is a nucleosome?

A

complex of DNA wrapped around a histone

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7
Q

how is DNA stored in prokaryotic cells?

A
  • prokaryotes also carry DNA in chromosomes but the DNA molecules are shorter + circular
  • DNA is NOT wound around histones and instead supercoils to fit in the cell
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8
Q

describe the DNA found in chloroplasts and mitochondria

A
  • short and circular
  • not protein bound
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9
Q

what are the three key features of the genetic code?

A
  • degenerate
  • universal
  • non-overlapping
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10
Q

what is a start codon? what does it do?

A
  • first codon on the DNA and mRNA
  • initiates translation
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11
Q

what is a stop codon? what does it do?

A
  • final codon
  • does not code for an amino acid + therefore there is no complementray anticodon with a particular amino acid
  • so in translation causes the ribosome to detach, therefore stopping translation
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12
Q

why is the genetic code described as being degenerate? why is this an advantage?

A
  • most amino acids can be coded for by more than one codon
  • if a point mutation occurs, even though the codon will be different, it may still code for the same amino acid and therefore have no effect
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13
Q

why is the genetic code described as being universal? why is this an advantage?

A
  • the same triplet of bases codes for the same amino acid in all organisms
  • means genetic engineering is possible
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14
Q

why is the genetic code described as being non-overlapping? why is this an advantage?

A
  • each base in a gene is only part of one codon that codes for one amino acid
  • therefore each codon is read as a discrete unit
  • if point mutation occurs, will only affect 1 codon and therefore only 1 amino acid
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15
Q

what are introns? where are they found?

A
  • sections of DNA that do NOT code for amino acids and therefore polypeptide chains
  • found in eukaryotic DNA but not in prokaryotic DNA
  • get spliced out of mRNA molecules
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16
Q

what are exons?

A

sections of DNA that code for a sequence of amino acids

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17
Q

what is a genome?

A

complete set of DNA in one cell

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18
Q

what is a proteome?

A

full range of proteins in one cell

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19
Q

compare a genome to a proteome

A
  • the genome is the complete set of DNA in one cell whereas the proteome is the full rangeof proteins one cell
  • genome should never change whereas the proteome of the cell is constantly changing depending on which proteins are currently needed
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20
Q

where does transcription take place?

A

nucleus

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21
Q

outline the process of transcription

A
  1. DNA helicase breaks hydrogen bonds between bases, helix unwinds + bases exposed and act as a template
  2. only one chain of the DNA acts as a template
  3. free mRNA nucleotides in nucleus align opposite exposed complementary DNA bases
  4. RNA polymerase bonds together the RNA nucleotides to form pre-mRNA
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22
Q

what happens to pre-mRNA after transcription?

A
  • has to be modified to become mRNA ready to leave the nucleus and take part in translation
  • introns are spliced out by splicesome proteins leaving only exons behind
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23
Q

outline the process of translation

A
  1. once modified mRNA left nucleus, attaches to ribosome in cytoplasm
  2. ribosome attaches to start codon
  3. tRNA molecule with complementary anticodon to start codon aligns opposite mRNA + is held in place by ribosome
  4. ribosome move along mRNA molecule to enable another complementary tRNA to attach next to codon on mRNA
  5. the 2 amino acids that were delivered by tRNA molecule are joined by a peptide bond - catalysed by an enzyme + requires ATP
  6. continues until ribosome reaches stop codon at end of mRNA molecule. stop codon doesnt code for amino acid + so ribosome detaches + translation ends
  • polypeptide is now created and will enter the golgi body for folding + modification
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24
Q

which 2 mechanisms introduce variation in organisms?

A
  • independent segregation (of homologous chromosomes)
  • crossing over (between homologous chromosomes)
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25
Q

what is independent segregation? how can the number of combinations this produces be calculated?

A
  • in meiosis 1, homologous pairs of chromosomes line up opposite each other at the equator of the cell
  • it is random which side of the equator the parernal and maternal chromosomes from each pair lie
  • these pairs are separated so one of each homologous pair ends up in the daughter cell, which creates a large number of possible combinations of chromosomes in the daughter cells produced
  • calculate using 2n, where n = number of homologous pairs (e.g. in humans 223)
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26
Q

what is crossing over?

A
  • when homologous pairs line up opposite each other at the equator in meiosis 1, parts of the chromatids become twisted around each other
  • this puts tension on the chromatids causing parts of the chromatids to break
  • broken parts of the chromatid recombine with another chromatid, resulting in new combos of alleles
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27
Q

compare meiosis and mitosis

A

meiosis: 2 nuclear divisions, haploid cell (one set of chromosomes), introduces genetic variation
mitosis: 1 nuclear division, diploid cells (two sets of chromosomes), creates genetically identical cells

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28
Q

how can meiosis be identified in a life cycle diagram?

A
  • meiosis invoves a diploid (2n) parent cell dividing to become a haploid cell (n), so look for where 2n becomes n
29
Q

other than independent segregation and crossing over, which other factor indroduces genetic variation? how can the new amount of combinations be calculated?

A
  • random fertilisation
  • creates new combos of alleles
  • there are (2n)2 combinations of chromosomes (before crossing over is considered)
30
Q

what is non-disjunction?

A

when the chromosomes or chromatids do not split equally during anaphase

31
Q

what is polyploidy? when does it occur?

A
  • changes in the whole sets of chromosomes
  • occurs when organisms have 3 or more sets of chromosomes rather than the usual 2
  • mainly occurs in plants
32
Q

how does polyploidy occur?

A
  1. each homologous pair is doubled due to DNA replication in interphase
  2. non-disjunction in meiosis 1, ALL chromosomes fail to separate equally
  3. normal division in meiosis 2, chromatids separate equally
  4. when the 2n gamete is joined with an n gamete in fertilisation, a 3n (triploid) is formed
  • non-disjunction may occur in meiosis 2 instead of meiosis 1
33
Q

what is aneuploidy? when does it occur?

A
  • changes in the number of individual chromosomes
  • sometimes individual homologous pairs of chromosomes fail to separate during meiosis, resulting in a gamete having one more or one fewer chromosome
  • on fertilisation with a gamete with the normal number of chromosomes, the resultant zygote will have more or fewer chromosomes than normal in all their body cells
34
Q

how does aneuploidy occur?

A
  1. each homologous pair is doubled due to DNA replication in interphase
  2. non-disjunction in meiosis 1, ONE chromosome pair fails to separate equally
  3. normal division in meiosis 2, chromatids separate equally
  4. when the n+1 gamete is joined with an n gamete in fertilisation, a 2n+1 zygote is formed
  5. when the n-1 gamete is joined with an n gamete in fertilisation, a 2n-1 zygote is formed
  • non-disjunction may occur in meiosis 2 instead of meiosis 1
35
Q

what is genetic diversity? why is it important?

A
  • number of different alleles of genes in a population
  • natural selection can only occur if there is genetic diversity within a population
36
Q

what is evolution?

A

change in allele frequency over many generations in a population

37
Q

what is natural selection? why is it necessary?

A
  • process that leads to evolution in populations
  • results in species becoming better adapted to their environment
  • adaptations may be anatomical, physiological or behavioural
38
Q

describe the process of natural selection

A
  1. new alleles for a gene are created by random mutations
  2. if the new alleles increase the change of survival for the individual organism then they are more likely to survive + reproduce
  3. this reproduction passes on the advantageous allel to the next generation
  4. as a result, over many generations the new allele increases in frequency in the population
39
Q

what is directional selection?

A
  • one of the extremes has the selective advantage
  • occurs when there is a change in environment
  • the modal trait changes
40
Q

what is stabilising selection?

A
  • the modal trait has the selection advantage
  • occurs when there is no change in environment
  • modal trait remains the same
  • standard deviation decreases as individuals with the extreme trait decreases
41
Q

what is a species?

A

a group of similar organisms that can breed to make fertile offspring

42
Q

what are courtship rituals?

A

a sequence of actions which is unique to each species and are how animals identify member of their own species to reproduce with

43
Q

explain why courtship is important

A

- enable successful reproduction:
- enables them to recognise own species and opposite sex
- synchronises mating behaviour - indicates sexually mature and in season (releasing egg)

- to ensure survival of offspring:
- form a pair bond
- choose a strong and healthy mate

44
Q

what determines a courtship ritual? explain how studying courtship rituals can be useful

A
  • courtship ritual genetically determined so the more similar a sequence is, the more similar their DNA base sequence is
  • the more similar a courtship ritual sequence between different species is, the more closely related the species are (allows us to see the relationships between different species)
45
Q

in the binomial system, what does the first name represent?

A

genus

46
Q

in the binomial system, what does the second name represent?

A

species

47
Q

why do different species look similar?

A
  • live in similar environment
  • have similar selection pressures
  • similar alleles will have the selection advantage
  • produces similar/same proteins + therefore have similar characteristics
48
Q

what is a hierarchy?

A

smaller groups arranged within larger groups, with no overlap between groups

49
Q

give an example of a hierarchy and the taxa it comprises

A
  • domain
  • kingdom
  • phylum
  • class
  • order
  • family
  • genus
  • species
50
Q

why is it necessary to organise organisms into hierarchies and taxas?

A

to understand relationships between organisms and track changes

51
Q

how were organisms originally classified? what are some more modern + accurate ways of classifiying organisms?

A
  • orginally based on visibible similarities (e.g. appearance, behaviour, fossils)
  • DNA sequence
  • mRNA sequence
  • amino acids sequence
  • immunological (comparing similarity in self-antibody shape)
52
Q

what is phylogenetic classification?

A
  • arranges species into groups according to their evolutionary origins and relationships
  • shows which species share common ancestors + how closely related they are
  • all organisms have evolved from shared common ancestors, which is shown on a phylogenetic tree
53
Q

what is species diversity?

A

the number of different species + individuals within each species in a community

54
Q

what is genetic diversity?

A

the variety of genes amongst all the individuals in a population of one species

55
Q

what is ecosystem diversity?

A

the range of different habitats

56
Q

what is species richness?

A

the number of different species in a particular area at the particular time

57
Q

how does farming reduce biodiversity?

A
  • destruction of hedgerows
  • selective breeding (narrows gene pool)
  • monocultures
  • overgrazing
  • filling in ponds and draining wetlands
58
Q

how can biodiversity be measured?

A
  • index of biodiversity is a measure of species diversity
  • calculation to measure the relationship between the number of species in a community + the number of individuals in each species
59
Q

what is the difference between species richness and index diversity?

A

index of diversity takes into account the numer of individuals in each species

60
Q

the formula for simpson’s diversity index is D = [ N(N-1) ] / Σn(n-1)
what variables to each of these letters represent?

A

D= Simpson’s diversity index (larger value = greater species diversity)
N = total number of organisms of all species
n = total number of organisms of a particular species

61
Q

what is an addition mutation?

A
  • one or more bases are added
  • usually causes a frame shift
62
Q

what is a deletion mutation?

A
  • one or more bases are removed
  • usually causes a frame shift
63
Q

what is a substitution mutation?

A
  • one or more bases replaced
  • could produce: stop codon, different amino acid or same amino acid (due to degenerative nature of the genetic code)
64
Q

what is a duplication mutation?

A
  • one or more bases repeated
  • usually causes a frame shift
65
Q

what is an inversion mutation?

A

group of bases separate from DNA sequence and rejoin in reverse order

66
Q

what is a translocation mutation?

A

group of bases separate from one chromosome and rejoin another chromosome

67
Q

what is a mutagenic agent?

A

increases the probability of a mutation occurring

68
Q

give 4 examples of mutagenic agents

A
  • UV radiation
  • ionising radiation
  • chemicals
  • viruses
69
Q

what is a silent mutation?

A

change in the nucleotide sequence that results in the same amino acid sequence

A-Level Biology (6 decks)

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