Unit 4 - Genetic Info, Variation & Relationships b/w Organisms Flashcards
define gene
sequence of DNA bases that code for a polypeptide or for a functional RNA (inc. rRNA & tRNA)
define locus
fixed position on a chromosome that a gene occupies
define allele
different versions of a gene
different alleles have slightly different nucleotide sequences but occupy the same locus on the chromosome
how are chromosomes arranged?
homologous pairs
one inherited from the father & one inherited from the mother
eukaryotic DNA vs prokaryotic DNA
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
how is DNA packaged in eukaryotes?
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)
what is the structure of a chromosome?
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
describe karyotype
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
what sex chromosomes correspond to each gender?
xy - male
xx - female
define genome
complete set of genes in a cell
define proteome
full range of proteins that a cell can produce
or coded for by the cell’s DNA
what are the features of genetic code?
triplet code
degenerate
non-overlapping
universal
describe triplet code
a sequence of 3 bases (codon) codes for a specific amino acid
describe degenerate code
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
describe non-overlapping code
each base in the sequence is only read once
code is always read in one direction along the DNA strand
describe universal code
DNA is the same in all organisms
same triplet code for same amino acids
why might mutations in nucleotide sequence of a gene not cause a change in structure of polypeptide?
triplets code for the same aa
mutation in introns/non-coding region
describe messenger RNA
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
describe the process of transcription
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, needing ATP
in eukaryotes, pre-mRNA is spliced & introns removed to form mRNA
describe the process of splicing
introns (non-coding sections) are removed
remaining exons (coding sections) join together
splicing does not happen in prokaryotes
compare DNA replication & transcription
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
describe tRNA
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 tRNA has a specific anticodon, which pairs with the complementary codon on the mRNA by H bonds
describe the process of translation
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
extra notes on translation
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
describe the role of ribosomes in translation
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
comparison of DNA, mRNA & tRNA
see table
describe the role of atp in the process of translation
releases energy
so aas join to tRNA & peptide bonds form b/w amino acids
how are gene mutations caused?
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
define mutagenic agent
a factor that increases the rate of gene mutations
most mutations have a negative/neutral impact on the fitness of an organism (selected against) but some are beneficial & selected for by natural selection
.
what are the types of base substitution mutations?
silent mutation
mis-sense mutation
non-sense mutation
all are single base substitutions
describe silent mutation
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
describe mis-sense mutation
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
describe non-sense mutation
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
describe frameshift mutation caused by deletion/addition base mutation
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
what is the function of meiosis?
produces four daughter gamete cells each with 1/2 the number of chromosomes as the parent cell & all genetically varied
meiosis involves 2 nuclear divisions
one diploid cell in reproductive organ (ovary/testes) divides twice to produce 4 haploid daughter cells, which are all genetically different
why is meiosis important?
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
other than meiosis, what causes genetic variation?
random gene mutations –> change in DNA base sequence
creates new alleles
random fertilisation = fusion of gametes –> new combinations of maternal & paternal alleles
summary of meiosis diagram
see notes
how does meiosis result in genetic variation?
crossing over of homologous chromosomes
independent segregation of homologous chromosomes
which causes new allele combinations
random fertilisation of gametes
describe the process of crossing over
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
describe independent segregation
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
what is the formula for # of possible gametes from independent segregation
2^# of homologous pairs
define chromosome mutations
changes in structure or number of chromosomes
why does non-disjunction happen?
1- homologous chromosomes fail to separate in meiosis 1
2- sister chromatids fail to separate in meiosis 2
what is the effect of non-disjunction?
in both cases, gametes are formed with either 1 extra or 1 missing chromosome
e.g. Down’s syndrome, Turner’s syndrome
define evolution
the changes in allele frequency & in characteristics that occur in a population of organisms over time
define genetic diversity
total number of different alleles of genes (for all the genes) in a population
it’s a factor that enables natural selection
define gene pool
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
define population
all individuals of the same species living in the same place & can interbreed
what are the 4 main principles of how natural selection works?
- genetic variation exists in a population of organisms
- one or more selection pressures act on the population
- the form that is best adapted to withstand selection pressure are more likely to survive & reproduce
- changes in characteristics of a population (evolution) occur over many generations
how does natural selection work?
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
define selection pressure
change in the environment that favours one form of organism over another
examples of selection pressures
competition
predation
disease
environmental factors: temperature, soil factors (e.g. pH, mineral content) (plants)
what do organisms compete for?
animals: for food, water, territory & mates
plants: space, sunlight, water & mineral ions
what causes extinction?
very strong selection pressures
what are the 2 types of selection?
directional & stabilising
describe normal distribution
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
define standard deviation
measure of the spread of the data around the mean value
describe directional selection
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
example of directional selection
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
describe stabilising selection
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
example of stabilising selection
human birth weights
how to answer natural selection 6 markers
- state variation occurs
- insert info from question
- variation due to random mutation –> new alleles
- selective advantage of new allele (insert info from question)
- more likely to survive & reproduce, passing on beneficial allele to offspring
- over time, increase in frequency of beneficial allele
what are the 3 types of adaptations
anatomical - structural
physiological - biological processes
behavioural
what is a species?
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
what is courtship behaviour?
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
how does courtship behaviour ensure mating is successful & offspring have the best chance of surviving?
it enables individuals to:
1. recognise members of their species to produce fertile offspring
- identify a mate capable of breeding - sexually mature, receptive & fertile
- form a pair bond - possible life-long monogamous bond leads to successful mating & raising of offspring
why is courtship behaviour important?
it maximises reproductive efficiency
it maintains reproductive isolation of a species
it allows females to pick the ‘fittest’ male
what is classification?
the process of placing living things into groups
(what are the reasons for classification?)
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
what is the binomial name for a species?
genus & species
capital letter for genus
what are groups of organisms called, what kind of system is it & what are they based on?
taxa
hierarchical system
organisms’ similarities & differences
what are the 2 features of a hierarchical system?
- smaller groups are found within larger groups
- there is no overlap b/w groups
what is the order of taxa?
domain
kingdom
phylum
class
order
family
genus
species
(what are the 3 domains & their features?)
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
define phylogeny
classification based on evolutionary origin
how do you interpret a phylogenetic tree?
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
what did Darwin’s theory of evolution suggest?
all living organisms share a common ancestor - ‘last universal common ancestor’
define phylogenetics
study of evolutionary relationships b/w species
what limited method can be used to compare species?
the frequency of measurable & observable characteristics
instead, what technologies are used to compare similarities & differences b/w species & why?
amino acid sequences
mRNA sequences
DNA sequences
comparison of Ab-Ag associations = immunological technique
bc they are more accurate
gene technology has caused a change in methods of investigating diversity…
measurable & observable characteristics replaced by direct investigation of DNA sequence
how are amino acid sequences used to compare species?
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
what is the limitation of using AA sequences/why is DNA sequencing better?
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
how are mRNA sequences used to compare species?
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
how are DNA sequences used to compare species?
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
what is the method for the immunological technique of comparing species?
- serum of blood proteins from human is injected into rabbit
Abs produced in rabbit’s blood attach to protein in human’s blood - the rabbit’s blood is taken & Abs that are anti-human protein are extracted
- 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
what do scientists use to get valid conclusions & why?
a number of sources & different methods
bc differing sources give differing results
define biodiversity
the range, proportion and variety of genes, species & habitats within a particular area at a given time
define species diversity
the number of different species & number of individuals in each species in a community
define species richness
the number of different species in a community
define genetic diversity
the number of different genes in a population (all individuals in 1 species)
how can biodiversity be measured?
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
the greater the index of biodiversity (d),
the greater the biodiversity & stability of an ecosystem so the greater the chance of surviving environmental change e.g. climate change
what is the formula for index of biodiversity?
d = N(N-1) / Σn(n-1)
N = total number of organisms of all species
n = total number of organisms of each species
why is agriculture increasing & what is the general effect on biodiversity?
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
what are the 4 pressures due to agriculture?
monoculture
pesticides
removal of hedgerows
fertilisers
what is monoculture & its effect?
having a field of 1 crop replacing a species-rich area
which decreases gene pool & number of alleles so genetic diversity & biodiversity decrease
what are the types of pesticides & what are their effect?
herbicides, insecticides, fungicides
can affect non-target species
toxic
can disrupt natural food chain
so biodiversity decreases
what is the + effect of removing hedgerows?
increased space for crops = more crop yield & more money for farmers
removes competition with crops for resources
why is there more species diversity in hedgerows?
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
what is the - effect of removing hedgerows?
reduced shelter for organisms
loss of habitats & niches
fewer plant species
so decreased range of food
so decreased species diversity & biodiversity
how do hedgerows reduce money spent on pesticides?
increase number of predators of pests
what is the effect of fertilisers? (+ & -)
+: 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)
what are the negative consequences of agriculture?
disruption of food chains
loss of natural predators
loss of species
reduced species richness
decrease in biodiversity
