Genetic info, variation and relationships between organisms (4) Flashcards
differences between prokaryotic (sometimes could be mitochondrial/chloroplast) DNA and eukaryotic DNA?
Eukaryotic is associated with histones, prokaryotic is not
Eukaryotic is linear and prokaryotic is circular
Eukaryotic is coiled up repeatedly to form chromosomes whereas prokaryotic is supercoiled to fit in the cell and is free-floating in the cytoplasm
Eukaryotic is much bigger than prokaryotic DNA - prokaryotic DNA is short and circular
Eukaryotic DNA has introns whereas prokaryotic DNA does not have introns
THEY BOTH FORM DOUBLE HELIX SHAPES WITH THEIR DNA
genome
the complete set of genes in a cell
proteome
the full range of proteins that a cell is able to code for and produce
what do the genes, that don’t code for polypeptides, code for?
they code for functional RNA such as tRNA and rRNA (transfer and ribosomal)
allele
the different variations of the same gene, as an allele can exist in more than one form - these forms are called alleles
what is different about the polypeptides that are coded for by alleles?
the order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide - amino acid sequence differs slightly
how many chromosomes do humans have?
46, 23 pairs
homologous chromosome pairs?
pairs of matching chromosomes
they are the same size and have the same genes - they could have different alleles
in a homologous pair, where would alleles be found that are coding for the same characterisitic?
found at the same fixed position on each chromosome in a homologous pair - A LOCUS
RNA is … whereas DNA is…
single stranded
double stranded
structure of tRNA?
single polynucleotide strand
folded into a clover shape
hydrogen bonds between specific base pairs - hold the molecule in shape
has a specific sequence of three bases at one end ‘anticodon’
an amino acid binding site at the other end
where does transcription take place in eukaryotes and prokaryotes?
euk –> nucleus
prok –> cyotplasm
in prokaryotes, what are the DNA strands separated by?
RNA polymerase
whereas in eukaryotes it is by DNA helicase which is attached to the RNA polymerase
differences between trna and mrna?
tRNA has hydrogen bonds between complementary base pairs and thus has a folded structure with a ‘clover like shape’
whereas mRNA has a linear shape and doesn’t have hydrogen bonds
tRNA has an anitcodon whereas mRNA has a codon
tRNA has an amino acid binding site whereas mRNA does not
mRNA has more nucleotides than tRNA
mRNAs have different lengths whereas all tRNAs are a similar/same length
describe transcription:
DNA helicase breaks the weak hydrogen bonds between the complementary base pairs between the two DNA strands causing the strands to separate
Only one strand is then used as a template
The free RNA nucleotides are attracted to the exposed bases and thus align according to complementary base pair ruling
So adenine –> uracil, thymine–>adenine cytosine –> guanine, guanine–>cytosine
RNA polymerase joins the nucleotides together by catalysing the formation of phosphodiester bonds between them
This forms pre-mRNA which contains introns, this is then spliced in order to remove the introns
what two molecules are ribosomes made from?
rRNA (ribosomal RNA) and proteins
describe translation:
mRNA strand leaves the nucleus through the nuclear pores and enters the cytoplasm
mRNA strand binds/attaches/associates with a ribosomes (small subunit)
The ribosome moves along the mRNA strand in order to form the polypeptide
The ribosomes has two binding sites so can ‘fit’ two tRNA molecules
the ribosomes moves to find the start codon on the mRNA strand
then the ribosome codes for a tRNA molecule with a complementary anticodon to the codon on the mRNA strand
the tRNA molecule brings a specific amino acid
the anitcodon on the tRNA binds to the codon found on the mRNA
A condensation reaction results in the formation of a peptide bond which joins two amino acids together
once an amino acid has been joined to the polypeptide then the tRNA molecule is released
the amino acids join together with the use of ATP
three things about the genetic code?
non-overlapping meaning that no codon shares its bases
degenerate meaning that more than one codon codes for a single amino acid
universal meaning that the same specific codons code for the same amino acids in all living things, we all share the same 20 amino acids
how many possible triplets are there?
64
not all triplets code for amino acids, what else do they code for?
some are used to tell the cell to stop production of a protein - stop signals e.g. UAG
also start signals at the start of the mRNA which tell the cell when to start protein production but these code for a specific amino acid called methionine
how do you find the amino acid coded for by a tRNA molecule?
the anticodon of the tRNA determines the amino acid
normal body cells contain what nuumber of chromosomes?
they contain the diploid number of chromosomes
meaning that each body cell contains a pair of each chromosome, one maternal and one paternal
diploid number of chromosomes for humans?
46
gametes have how many chromosomes?
a haploid number of chromosomes, they only contain one copy of each chromosome in a homologous pair
haploid no. of chromosomes for humans?
23
fertilisation?
haploid egg cell fuses with a haploid sperm cell creating a diploid (2n) zygote
fertilisation is?
random fertilisation of gametes
what does random fertilisation of gametes result in?
produces zygotes with DIFFERENT COMBINATIONS OF CHROMOSOMES to both parents
the mixing of genetic material in sexual reproduction increases genetic diversity within a species
where does meisosis take place in humans?
ovaries and testes
meiosis produces different products in humans compared to other organsims such as plants,insects. Describe the difference?
meiosis in humans and other mammals produces gametes directly
in other organisms it produces haploid cells which later divide by mitosis to form gametes
cells that divide by meiosis compared to cell produced by meiosis?
cells that divide are originally diploid, those that are produced are haploid
what happens in the first division of meiosis compared to the second division of meiosis?
1st - the homologous chromsomes pairs separate
2nd - the chromatids separate
Describe the process of meiosis?
Before meiosis begins, the DNA unravels and replicates so that there are 2 copies of each chromosome, each copy is called a chromatid
e.g. I (chromsome) –> II (two chromatids)
the DNA then condenses to form double-armed chromosomes, each made from two sister chromatids - these are joined in the middle by a centromere
Meiosis 1 (1st division) the chromosomes randomly arrange themselves in pairs and then these homologous pairs are separated, halving the number of chromsomes
Meiosis II - the pairs of sister chromatids are now separated and the centromere divides
FOUR HAPLOID cells that are GENETICALLY DIFFERENT are produced
describe the appearance of the chromosomes throughout meiosis:
I I
I I
I-I-I-I (dna unravels+replicates)
I-I-I-I
II II (DNA condenses)
II II
II II (dna arranges into homo pairs)
II II (randomly)
II II
II II
homo pairs separated
I I I I
I I I I
Sister chromatids separated
4 daughter cells produced
describe the behaviour of the chromosomes in terms of ‘n’ :
2n
2 x 2n
2 x 2n
2 x 2n (randomly arranged into homo pair)
2 x n 2 x n
n n n n
in any diploid species, how do you work out the number of possible combinations of maternal and paternal chromosomes?
2 (to the power of n)
where n represents the diploid number of chromosomes
so humans would be 2 (23) so there would be 8,388,608 possible combinations of chromosomes
when does the crossing over of homologous chromosomes occur?
during meiosis 1
describe crossing over?
homologous pairs of chromosomes asociate to form a bivalent
Chiasmata form
lengths of non-sister chromatids/alleles are exchanged
Producing new combinations of alleles
independent segragation?
when homologous pairs are separated in meiosis 1, it is completely random which chromosome from the pair goes to which daughter cell
crossing over AKA?
recombination
what does crossing over result in?
the daughter cells formed from meiosis II contain chromatids with different alleles
do prokaryotes divide by meiosis?
no nor do they reprodcue sexually
how do zygotes divide?
by mitosis
difference between meiosis and mitosis:
mitosis = 2 daughter cells
meiosis = 4
mitosis = genetically identical
meiosis = genetically different
mitosis = no genetic variation
meiosis = indep seg / crossingover
mitosis = produces cells w/same no. of chromosomes
meiosis = produces cells w/ half no. of chromosomes
what is the mutation that causes a change in the number of chromosomes?
chromosome non-disjunction
Define term ‘mutagenic agent’?
a factor that increases the rate of mutations in the base sequence of DNA/mRNA
e.g. ionising radiation (X-ray, gamma rays) UV radiation, chemicals, viruses
they increase the probability of a mutation occurring
mutations are always…
random
chromosome non-disjunction?
homologous pairs of chromosomes do not separate properly/evenly
During meiosis
there is an error that occurs during meiosis
chromosome mutation can lead to inherited conditions e.g. downs – chromosomes non-disjunction is a type of chromosome mutation
why is a high genetic diversity good?
allows populations/organisms to adapt to changing enviornmental conditions
how is genetic diversity increased in a population?
mutations in the DNA forming new alleles (advan)
different alleles being introduced into a population when individuals from another population migrate into it and reproduce –GENE FLOW
diversity within a species?
all members of a species have the same genes, the diversity is down to the different alleles present in the species
gene pool?
complete range of alleles in a population
genetic bottleneck?
an event that causes a big reduction in a population - large no. die before reproducing
reduces the number of different alleles in the gene pool and so reduces genetic diversity
the survivors reproduce and the a larger pop. is created from fewer individuals thus decreased no. of different alleles and decreased genetic diversity
founder effect?
just a few individuals start a new colony, small number of different alleles in the INITIAL gene pool
frequency of each allele in the new colony is very different to the frequency of each allele in the original population
e.g. previously rare allele may now be more common, higher chance of genetic disease
organisms with a selective advantage are what?
organisms that are well adapted to their environment have a selective advantage over the less-well adapted organisms
adaptation?
features that help organisms to survive in their enviornment
can be behavioural, physiological or anatomical
beneficial allele?
increases in frequency over many generations
behavioural adaptation?
the way an organism acts that increases chance of survival
e.g. possum play dead
e.g. scorpion dance ensure attracts right mate increases chance of reproduction
physiological adaptation?
processes inside organism’s body that increase chance of survival
e.g. bears hibernate during winter slow down metabolism to conserve energy so don’t need to look for food when scarce
e.g. some bacteria produce anitbiotics to get rid of any competition by killing other bacteria species
anatomical adaptations?
structural features of organism’s body to increase chances of survival
e.g. otter’s streamlined body
e.g. whale’s thich layer of blubber(fat)
directional selection example?
antibiotic resistance
stabilising selection example?
human birth weights
directional seletion?
where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce - could be in response to an environmental change
directional selection - movement of mean?
mean shifts in the direction that is favoured for e.g. high antibiotic resistance so mean would shift RIGHT
stabilising selection?
where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
it occurs when the environment isn’t changing and it reduces the range of possible characteristics
if the variation stays roughly the same but the MEAN increases, what type of selection is it?
directional
if the variation changes but the mean stays the same then it is?
stabilising
what is a liquid broth a mixture of?
distilled water, nutrients, bacterial culture
what is the negative control for testing the effects of antibiotics on an agar plate of bacteria?
it is not expected to have any effect on the experiment - it should show that the other results must be due to the presence of the antibiotics not the paper disc
IT IS A PAPER DISC SOAKED IN STERILE WATER ONLY
Why don’t you completely seal the petri dish with tape before incubation?
it will prevent oxygen from entering the dish, this may encourage the growth of anaerobic diesease causing bacteria
DON’T OPEN THE DISH AFTER INCUBATION
antiseptics?
non-selective chemicals that prevent the growth of microorganisms - used on living tissue
Disinfectants?
non-selective chemicals that prevent the growth of microorganisms - used on non-living objects e.g. counter surfaces
what are aseptic techniques used for?
to avoid contamination of the sample from outside microorganisms
describe some aseptic techniques:
Wash hands with soap/disinfect surfaces/disinfect surfaces - to kill/remove microbes
Use sterile pipette/syringe to transfer bacteria
Remove bottle lid and flame neck of bottle of broth- to prevent contamination as it causes microorganisms to move up away from the container so they don’t fall in as hot air rises
Lift lid of agar plate at an angle - to prevent entry of any microbes
Work close to upward air movement
Burning bunsen close by to create upward current of air
Use sterile spreader
Place pipette/spreader into disinfectant immediately after use
what is turbidity?
the measure of the cloudiness of a liquid
taxonomy
classifies organisms
phylogeny
phylogenetic tree to see how closely related organisms are
species
group of organisms that is able to successfully reproduce to give fertile offspring
what is the naming system used for classification?
the binomial system
what is the binomial naming system useful for?
allows scientists to communicate about organisms in a standard way which helps to avoid confusion
what is courtship behaviour?
it is species specific - so only members from a particular species will do or respond to that behaviour = recognition
it is carried out by organisms to attract a mate can be carried out by male/female/both
it can be used to classify species
e.g. dance, building, releasing chemicals, using sound, puffing chest
more closely related? (courtship)
the more similar their patterns for their courtship behaviour
courtship behaviour? spec def
a necessary precursor to successful mating
how do we clarify evolutionary relationships?
genome sequencing
comparing amino acid sequences
immunological comparison
genome sequencing
advances in genome sequencing has allowed us to determine the entire base sequence of an organism’s DNA
the more closely related = the higher percentage of similarity of the DNA base sequence between organisms
comparing amino acid sequences
the sequence of amino acids is coded for by the base sequence of DNA
closely related organisms have similar DNA base sequences so their amino acid sequence is also similar in their proteins
immunological comparison
similar proteins will bind to the same antibodies
e.g. if antibodies to a human version of a protein were added to isolated samples from other species, any protein that is similar to the human version, the anitbody will bind to it
how can we use immunological comparison to determine how similar the proteins are?
when an antibody binds to a protein it forms a precipitate in solution
the more antibodies the protein binds, the more ppt will form so the amount of ppt can be used to determine how similar two proteins are
the distance along the gene sequence is given as:
bp
base pairs
antibodies are often linked to a fluorescent protein, what does this allow?
allows the antibodies to be detected once they have bound to a protein
genetic diversity?
number of different alleles in a population
how can we determine genetic diversity directly?
- different alleles of the same gene will have slightly different DNA base sequences - comparing these allows scientists to find out how many alleles of that gene are in the population
- different alleles will produce slightly different mRNA base sequences and may produce proteins with slightly different AA sequences - these can be compared
variation between species and within a species?
within –> different alleles
between –> different genes
variation can also be caused by environmental factors
interspecific variation
different species
intraspecific variation
same species
what does random sampling ensure?
removes bias
describe a normal distribution on a graph:
bell shaped graph
it is symmetrical about the mean
one that isn’t a normal distribution would show a skewed graph
standard deviaiton?
a measure of the spread of values ABOUT THE MEAN
a wider graph of normal distribution would mean what for the standard deviation?
the standard deviation would be large
values with a larger standard deviation show what?
greater variation
if p value is LESS than 0.05 then…
significant - less than 5% probability that it is due to chance
why is using the mean better than using the range to calculate the dispersion of data?
because the mean takes into account all of the values whereas the range only takes into account two values so the range is more likely to be affected by an anomalous result
smaller error bars?
= smaller standard deviation and the less that data sample vaires
habitat
the area where an organism or a population lives
community
all of the populations of all the different species living in a habitat
biodiversity
variety of living organisms in an area
how can we measure biodiversity?
species richness
index of diversity
species richness
the number of different species within a community
however, the population size of each of these species should also be taken into account as a very small pop of a certain species should not be treated the same as a large pop of another species - this is where the index of diversity comes in
index of diversity
takes both the number of different species in a community and the abundance of each species into account
how do farming techniques reduce biodiversity?
MONOCULTURE- reduces plant diversity directly, supports fewer organisms further reducing biodiversity
HERBICIDES - kill unwanted plants reducing plant diversity and reduces no. of organisms that feed
PESTICIDES - kill organisms that feed on crops, reduces diversity directly by killing pests but also the birds that have their food source taken away
removal of HEDGEROWS
removal of WOODLAND
BOTH: done to increase area of farmland, directly reduces number of trees/hedges and thus reduces diversity but also destroys habitats lose shelter and food source species may die or be forced to migrate
how do we work out the correlation between two variables?
by calculating the spearman’s rank correlation coefficient
explain spearman’s rank correlation coefficient:
+1 perfect positive correlation
-1 perfect negative correlation
Closer to 0 the weaker the correlation
spearman’s rank correlation coefficient if your value is higher than the p value then:
reject null hypothesis, the result is statistically significant
