genetic info, variation & relationships Flashcards
1
Q
what is a gene? (3) (genetic info)
A
- a section of DNA at a locus (particular position) on a DNA molecule
- codes for the amino acid sequence of a polypeptide & a functional RNA (ribosomal & transfer)
- made up of a specific sequence of bases along the DNA molecule
2
Q
why do scientists theorise that there are 3 bases that code for each amino acid? (5) (genetic info)
A
- only 20 amino acids regularly occur in proteins
- only 4 different bases (A, T, C, G) are present in DNA
- if each base coded for an amino acid, only 4 different amino acids could be coded for
- using a pair of bases, 16 (4 X4) different codes are possible (still inadequate)
- 3 bases produce 64 different codes (enough for 20 amino acids)
3
Q
why is each different code called a triplet? (genetic info)
A
- it holds three bases for each amino acid
4
Q
outline 8 features of the genetic code (genetic info)
A
- a few amino acids are coded for by a single triplet
- remaining amino acids are coded for between 2 & 6 triplets each
- code is known as a ‘degenerate code’ as most amino acids are coded for by more than 1 triplet
- a triplet is always read in one particular direction along the DNA strand
- the start of a DNA sequence that codes for a polypeptide is always the same (methionine). If this first molecule doesn’t form part of the final polypeptide chain it is later removed
- three triplets don’t code for any amino acids. These are ‘stop codes’ & mark the end of a polypeptide chain
- code is non-overlapping (each base sequence is read only once)
- code is universal (with a few minor exceptions each triplet codes for the same amino acid in all organisms). This is indirect evidence for evolution
5
Q
outline the differences in DNA structure in prokaryotes & eukaryotes (6) (genetic info)
A
prokaryotes:
- circular
- not wrapped around histones
- made of nucleotides
- short
- plasmids
- no introns
eukaryotes:
- line at
- wrapped around histones
- made of nucleotides
- long
- no plasmids
- introns
6
Q
which two eukaryotic sub-cellular structures have a similar form of DNA to prokaryotes? (genetic info)
A
- chloroplasts
- mitochondria
7
Q
why do chromosomes appear as two attached chromatids at the start of division? (genetic info)
A
- because DNA has already been replicated to give two identical DNA molecules
- DNA is held by histones
8
Q
what is a homologous pair of chromosomes? (4) (genetic info)
A
- a pair of matching chromosomes that have the same genes
- don’t necessarily have the same alleles
- referred to as the diploid number (46 in humans)
- one chromosome is provided by each parent
9
Q
what is an allele? (3) (genetic info)
A
- one of a number of alternative forms of gene
- each individual inherits one allele from each parent
- can be the same or different
10
Q
what happened when two alleles are different? (genetic info)
A
- each allele has a different sequence, therefore a different amino acid sequence, so produces a different polypeptide
11
Q
what do base changes to a gene cause? (4) (genetic info)
A
- results in a new allele being produced, so a new sequence of amino acids being coded for
- this results in a different polypeptide being produced & therefore a different protein
- this protein may not function well/at all
- in an enzyme, it may change shape so its substrate no longer binds to it because the active site is no longer complimentary (causes issues for organism)
12
Q
what is a codon? (genetic info)
A
- the sequence of 3 bases on mRNA that codes for a single amino acid
13
Q
define ‘genome’ (genetic info)
A
- the complete set of genes in a cell
- includes DNA in the mitochondria & chloroplasts
14
Q
define ‘proteome’ (genetic info)
A
- the full range of proteins produced by the genome
- sometimes refereed to as the complete proteome (in which case ‘proteome’ refers to the proteins produced by a given type of cell under a certain set of conditions
15
Q
state what RNA is made up off & the two types that are important in protein synthesis (genetic info)
A
- made up of a ribose pentose sugar, an organic base (A, U, C, G) & a phosphate group
- messenger RNA (mRNA) & transfer RNA (tRNA) are important in protein synthesis
16
Q
what is mRNA? Describe its role in protein synthesis (6) (genetic info)
A
- a long strand of mononucelotides that is arranged in a single helix
- base sequence in determined by the sequence of bases on a length of DNA during transcription
- there is many types
- once formed, mRNA leaves the nucleus via the nuclear pores (in the nuclear envelope) & enters the cytoplasm, where it associated with the ribosomes
- it then acts as a template for protein synthesis
- it’s structure it suited to its functions as it has info in the form of codons. This sequence of codons determines the amino acid sequence of a specific polypeptide that will be made
17
Q
what is tRNA & what is its role in protein synthesis? (7) (genetic info)
A
- a small molecule that is made up of around 80 nucleotides
- single stranded chain folded into a clover-leaf shape (with one end of the chain extending beyond the other - this is the part of tRNA that an amino acid can easily bond to)
- there are many types, each of which binds to a specific amino acid
- at the opposite end of a tRNA molecule is the anticodon (a sequence of 3 other organic bases)
- the genetic code id degenerate so there must be as many tRNA molecules as there are coding triplets
- however each tRNA molecule is specific to an amino acid acid & has an anticodon that is specific to that amino acid
- tRNA is structurally suited to its role of lining up amino aids on the mRNA template during protein synthesis
18
Q
what is an anticodon? (genetic info)
A
- a sequence of 3 organic bases at the end of a tRNA molecule opposite the end chain
19
Q
What happens to tRNA molecules during protein synthesis? (genetic info)
A
- an anticodon pairs with 3 complimentary bases that make up the codon on the mRNA molecule
20
Q
how are mRNA & tRNA suited to their roles in protein synthesis? (genetic info)
A
- mRNA is structurally suited to its role as it has info in the from of codons. This sequence of codons determines the amino acid sequence of a specific polypeptide that will be made
- tRNA’s end chain is for attaching amino acids & its anticodon is for complimentary base pairing with the codon of an mRNA molecule, so is suited to line up amino acids on the mRNA template
21
Q
outline the differences in structure, function & composition of DNA, mRNA & tRNA * (8) (genetic info)
A
DNA:
- double polynucleotide chain
- largest molecule of the 3
- double helix
- pentose sugar is deoxyribose
- organic bases are A, T, C, G
- found mostly in the nucleus
- quantity is instant for all cells of a species (except gametes)
- chemically very stable
MRNA & tRNA:
- single polynucleotide chain
- mRNA = smaller than DNA but larger than tRNA, tRNA = smallest molecule of the 3
- mRA = single helix (except for a few viruses), tRNA = clover chapped molecule
- pentose sugar is ribose
- organic bases are A, U, C, G
- made in the nucleus bout found throughout the cell
- quantity varies from cell to cell & with level of metabolic activity
- mRNA = least chemically stable, tRNA = less chemically stable than DNA but more stable than mRNA
22
Q
briefly outline the process of protein synthesis (4) (genetic info)
A
- DNA provides the instructions in the from of long sequences of bases
- a complimentary section of this sequence is made in the form of pre-mRNA (transcription)
- the pre-mRNA is spliced to from mRNA
- the mRNA is used as a template to which complimentary tRNA molecules attach & the animo acids they carry are linked to from a polypeptide (translation)
23
Q
describe the process of transcription (4) (genetic info)
A
- 1) DNA helical breaks the hydrogen bonds between the 2 strands, causing them to separate & expose the nucleotides bases
- 2) complimentary RNA nucleotides move into place & from hydrogen bonds with the bases of the exposed nucleotides (C —> G, G —> C, A —> U, T —> A)
- 3) RNA polymerase joins the RNA nucleotides to the strand by forming phosphodiester bonds
- 4) when the RNA polymerase reaches ‘stop’ triplet code, it detaches & the pre-mRNA strand is complete
24
Q
which type of cell does splicing take place in & why? (genetic info)
A
- eukaryotes
- introns are uncommon/don’t exist in prokaryotes
25
outline the process of slicing (2) (genetic info)
- intervening introns would prevent the synthesis of a polypeptide
- the base sequences corresponding to the introns are removed & the functional exons are joined together
26
outline the process of translation (6) (genetic info)
- once a molecule of mRNA has been transcribed, it moves out of the nucleus via a nuclear pore (in the nuclear envelope)
- in the cytoplasm, the mRNA combines with a ribosome
- amino acids become attached to tRNA molecules in the cytoplasm. Each tRNA molecule is specific to one amino acid & has an anticodon (sequence of 3 bases) that is complimentary to the codons on the mRNA molecule
- tRNA molecules attach to the ribosome & their anticodon pairs up with the appropriate codons on the mRNA strand
- the AAs transported by the tRNA molecules link together via peptide bonds & the tRNA molecules return to the cytoplasm to pick up more amino acids
- the ribosome moves along the mRNA strand & the AAs continue to join together until all the codons have been translated & the polypeptide is complete (ends when the ribosome reaches & recognised a ‘stop codon’
27
what happens to a completed polypeptide chain after protein synthesis? (3) (genetic info)
- the finished polypeptide is coiled or folded to produce its secondary structure
- the secondary structure is folded to produce the tertiary structure
- different polypeptide chains (along with any non-protein groups) are linked to form the quaternary structure
28
what is a gene mutation? (genetics)
- any change to one or more nucleotide bases, or a change in the sequence of bases, in DNA
29
outline & explain the 3 base substitution mutations (genetics)
- nonsense mutation: a base substitution that leads to a new codon that codes for a ‘stop’
- it leads to a truncated protein that is often unfunctional
- silent mutation: a base substitution that leads to a new codon that codes for the same amino acid as the original codon
- it has no effect on the protein
- Miss ensue mutation: a base substitution that leads to a new new codon that codes for a different amino acid to the original codon
- it has variable effects on the tertiary structure & function of a protein
30
which type of gene mutation is an example of a fame shift mutation? (genetics)
- base deletion
- base substitution is not a frame shift mutation
31
outline & explain a base deletion mutation (genetics)
- deletion mutation: a base deletion that causes each codon after to be read in a different reading frame
- a base is entirely removed
- has a big change to the primary sequence of the protein
32
what are diploid & haploid cells? (genetics)
- haploid = cells that only contain a single copy of each chromosome (gametes)
- diploid = cells in which the nucleus contains two sets of chromosomes
33
what is meiosis? (genetics)
- a process of cell division that produces 4 unique, haploid gametes (daughter cells)
- a diploid cell undergoes 2 divisions
34
why is meiosis important for sexual reproduction? (2) (genetics)
- in fertilisation, a haploid sperm nucleus fuses with a haploid egg nucleus, creating a zygote (which has the normal number of diploid cells)
- fertilisation is random - the zygote produced can have a random combination of chromosomes from both parents
35
how many sets of chromosomes does every diploid cell have? (genetics)
- 2 complete sets
- one comes from each parent
36
how many divisions occur in meiosis? (genetics)
- 2 nuclear divisions occur
37
what happens during meiosis 1 & 2? (genetics)
meiosis 1:
- introduces genetic diversity by randomly giving a cell’s genes in 2
- homologous chromosomes pair up & their chromatids wrap around each other
- equivalent proportions may be exchanged by crossing over
- by the end, the homologous pairs have separated, with one chromosome from each pair going into one of the daughter cells
meiosis 2:
- similar to mitosis
- each chromosome is split into its two chromatids
- chromatids move apart
- by the end, four unique daughter cells have been formed (in humans they contain 23 chromosomes)
38
state the 8 stage ‘meiosis chain’ (genetics)
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
39
state 2 ways in which meiosis brings about genetic variation (genetics)
- independent segregation of homologous chromosomes
- new combinations of maternal & paternal alleles by crossing over
40
outline the process of independent segregation during meiosis (5) (genetics)
- during meiosis 1 each chromosome lines up alongside its homologous partner
- when the arrange themselves in this line they do so at random
- one of each pair will pass to each daughter cells meiosis
- which one goes to the daughter cell (& which of any other pairs) depends of how the pairs are lined up in the parent cell
- since they are lined up at random, the combination of chromosomes of maternal & paternal origin that go into the daughter cell at meiosis 1 is also a matter of chance
41
how is variety produced from genetic combinations? (3) (genetics)
- each member of a homologous pair has exactly the same genes & therefore determines the same characteristics
- however, the alleles of the genes may differ
- the independent assortment of these chromosomes therefore produces new genetic combinations
42
what is the equation for number of possible chromosome combination? (genetics)
- 2 to the power of n
- n = number of pairs of homologous chromosomes
43
what is the equation for number of possible gamete combinations? (genetics)
- (2 to the power of n) squared
- n = number of pairs of homologous chromosomes
44
what are crossing over & recombination during meiosis? (genetics)
- crossing over = chromatids cross over one another many times
- recombination = broken off portions of chromatic recombine with another chromatid
45
outline the process of crossing over (5) (genetics)
- the chromatids of each pair become twisted around one another
- during this twisting process, tensions are created & portions of the chromatids break off
- these broken portions might then rejoin with the chromatids of its homologous partner
- usually it is the equivalent portions of homologous chromosomes that are exchanged
- in this way new genetic combinations of maternal & paternal alleles are produced
46
what is an allele? (genetic info)
- one of a number of alternative forms of a gene
47
what is genetic diversity? (genetic info)
- the total number of different alleles of genes in a species/population
48
what is a population? (genetic info)
- a group of individuals of the same species that live in the same place & can interbreed
49
what is the relationship between numbers of different alleles in species & genetic diversity? (genetic info)
- the greater the number of different alleles that all members if a species possess, the greater the genetic diversity of that species
50
when is genetic diversity reduced? (genetic info)
- when a species has fewer different alleles that all
51
explain how genetic diversity can help a population to survive environmental change (2) (genetic info)
- the greater the genetic diversity, the more likely that some individuals in a population will survive an environmental change due to a wider range of alleles & therefore a wider range of characteristics
- this gives a greater probability that some individuals in will possess a characteristic that suits it to the new environmental conditions
52
what process does genetic diversity allow to take place? (genetic info)
- natural selection
53
why is genetic diversity important? (2) (genetic info)
- without it organisms may not be able to adapt to changes in the environment
- this means that single event can wipe out the whole population (e.g. pathogenic or environmental event)
54
how can genetic diversity within a population be increased? (2) (genetic info)
- by mutations in DNA forming new alleles (some advantageous & some harmful)
- through different alleles being introduced into populations from migrated species which reproduce with existing species
55
outline how a genetic bottleneck reduces genetic variation (3) (genetic info)
- an event (e.g. natural disaster) causes a big reduction in the population of a species (organisms die before reproducing)
- this reduces the number of different alleles in the gene pool, so reduces genetic diversity
- the survivors reproduce & a larger population is created from a few individuals with a reduced number of allies for different traits
56
explain how the founder effect reduces genetic variation (3) (genetic info)
- a few organisms in the original population start a new colony in which there are only a small number of different alleles in the initial gene pool
- alleles which appeared infrequently in the original population will increase in the new population, but will also reduce genetic diversity of the new population
- reasons for the founder group = migration, religion & geographical barrier
57
why aren’t all alleles of a population equally likely to be passed on to the next generation? (genetic info)
- because only certain individuals are reproductively successful & so pass on their alleles
58
outline the process of natural selection (6) (genetic info)
- within any population of a species there will be a gene pool containing a wide variety of alleles
- random mutations of these alleles may result in a new allele of a gene, which can be either harmful or advantageous
- if the allele is advantageous, it can increase the chance of the organism surviving, reproducing & passing their beneficial gene on to the next generation
- a greater proportion of the next generation inherits the new allele
- therefore the frequency of the allele will increase from generation to generation
- over generations this leads to evolution as advantageous alleles become more common in a population
59
what is evolution? (genetic info)
- a change in the allele frequency in a population
60
when can new species arise? (2) (genetic info)
- reproductive separation of 2 populations can result in the accumulation of difference in their gene pool
- occurs when these genetic differences leads to an inability of members of the population to interbreed to produce fertile offspring
61
what is selection? (genetic info)
- whereby organisms survive & reproduce depending on their characteristics
62
what is directional selection? (3) (genetic info)
- selection favours individuals that vary in one direction from the mean of population
- it changes the characteristics of the population
- results in phenotypes at one extreme of the population being selected ‘for’ & those at the other extreme being selected ‘against’
63
what is stabilising selection? (2) (genetic info)
- selection favours average individuals
-it preserves the characteristics of a population
- results in phenotypes around the mean being selected ‘for’ & those at both extremes being selected ‘against’
64
outline the process of directional selection (5) (genetic info)
- the environmental condition changes, which creates a selectional pressure
- those with phenotypes best suited to the new conditions are most likely to survive
- some individuals that fall to either side of the mean will possess a phenotype more suited to the new conditions
- these individuals will be more likely to survive & reproduce & will therefore contribute more offspring (& the alleles they possess) to the next generation
- over time the mean will move in the direction of these individuals
65
outline the process of stabilising selection (4) (genetic info)
- if environmental conditions remain stable, it is the individuals with phenotypes closest to the mean that are favoured
- these individuals a are more likely to survive & reproduce, & therefore pass their alleles to the next generation
- those individuals with extreme phenotypes are less likely to reproduce & pass on their alleles
- this means that the extreme phenotypes are usually eliminated from the population over time
66
outline the 3 types of adaptation that natural selection can lead to (genetic info)
- anatomical: structural features of an organism that aid its survival (e.g. shorter ears & thicker fur in arctic foxes compared to foxes in warmer climates)
- physiological: processes that occur within the body of an organism that help it to survive (e.g. oxidant of fats instead of carbohydrates in kangaroo rats to produce additional water in a dry desert environment)
- behavioural: traits that have been selected for because they help increase an organism's chance of survival and reproduction (e.g. the autumn migration of swallows from the UK to Africa to avoid food shortages in the UK winter)
67
what is classification? (2) (genetic info)
- the organisation of living organisms into groups
- process isn’t random but is based on several accepted principles
68
what can species breed to produce & what does this mean related to genes? (3) (genetic info)
- produce viable & fertile offspring
- they are therefore able to produce more offspring
- this means that (when a species reproduces sexually) any of the genes of its individuals can be combined with any other
69
what is the binomial naming system? (3) (genetic info)
- universal naming system based on Latin or Greek names
- the first (generic) name shows which genus the species belongs to
- the second (specific) name shows the pieces that the organism belongs to (this is never shared by any other species within the genus)
70
outline the 3 rules of the binomial naming system (genetic info)
- names are written in italics, or if they are handwritten are underlined to indicate that they are scientific names
- the first letter of the generic name is in uppercase, but the first letter of the specific name is in lower case
- if the specific name is unknown in can be written as ‘sp’ (should be underlines)
71
what does courtship behaviour enable to help individuals to survive? (5) (genetic info)
- recognise members of their own species to ensure mating only occurs between members of the same species (because only members of the same species can produce fertile offspring)
- identify a mate that is capable of breeding beucase both partners need to be sexually mature, fertile & receptive to mating
- form a pair bond that will lead to successful mating & raising of offspring
- sunchronise mating so that it takes place when there is the maximum probability of the sperm & egg meeting
- become able to breed by bringing a member of the opposite sec unto a physiological state that allows bredding to occur
72
why is coursthip behaviour used by males? (genetic info)
- to determine if a female is in a receptive stage (where is is likely the sperm & egg will meet)
73
what is artificial classification? (2) (genetic info)
- divides organsimsm according to differences that are useful at the time (e.g. colour, size, number of legs)
- these are analogous characterstics (have the same function but don’t have the same evolutionary origins)
74
what are anlogos charactersitc & what type of classification do they relate to? (2) (genetic info)
- characteristic with the same function but not the same evolutionary origins
- related to artificial classification
75
what is phylogenetic classification? (
- based on the evolutionary relationships between organisms & their ancestors
- classifies species into groups using shared features derived from their ancestors
- arranges the group into a hierarchy (where the groups are contained within larger composite groups with no overlap)
- relationhsips are partly based on homologus characteristics (have similar evolutionary origins regardless of their functions)
76
what are homologous characteristics & what type of classification are they related to? (2) (genetic info)
- characteristics with similar evolutionary origins regardless of their functions in an adult of a species
- associated with phylogenetic classification
77
what is taxonomy? (genetic info)
- the theory & practice of biological classification
78
what ar taxons/taxa? (2) (genetic info)
- taxon = singular, taxa= plural
- each groups within a phylogenetic classification
79
80
what are taxonomic ranks (hierarchal order) based on & what is the highest)? (2) (genetic info)
- based on the evolutionary line of descent of the group members
- highest = domain
81
state the classification ranks (8) (genetic info)
- domain
- kingdom
- phylum
- class
- order
- family
- genus
- species
82
what is pholegny? (genetic info)
- the evolutionary relationships between organisms
83
how are phylogenetic relstionships presented? (3) (genetic info)
- in phylognetic tree diagrams
- oldest species is at the base of the tree & the most recent ones are represented by the ends of branches
- the closer the branches, the closer the evolutionary relationships
84
what is biodiversity? (3) (genetic info)
- describes variety in the living world
- refers tot he number & variety of genes, species & habitats within a particular region
- made up of the components genetic diversity, species diversity ecosystem diversity
85
what is species diversity? (genetic info)
- the number of different species & number of individuals within any one community
86
what is genetic diversity? (genetic info)
- the variety of genes possessed by the individuals that make up a population of a species
87
what is ecosystem diversity? (genetic info)
- the range of different habitats 9froma small local one to the whole Earth)
88
what is species richness? (2) (genetic info)
- the number of different species in a particular area (community) at any given time
- can be used as a measure of species diversity
89
state the index for calculating species diversity & what each part means (6) (genetic info)
- d = N(N-1) ÷ ∑n(n-1)
- d = index diversity
- N= total number of organsims of all species
- n = total number of organisms of each species
- ∑ = sum of
- the higer the value of d, the greater the species diversity
90
91
what is an index diversity (genetic info)
- describes the relationships between the number of spcieces in a community & the number of individuals in each species
