Topic 4B - Diversity, classification and variation ARN * Flashcards
meiosis and genetic variation mutations genetic diversity and natural selection investigating selection classification of organisms DNA technology, classification and diversity investigating variation biodiversity
what are gametes?
sperm cells in males and egg cells in females.
they join together at fertilisation to form a zygote, which divides and develops into a new organism
what is the diploid number?
the number of chromosomes normal body cells have, denoted 2n. so each cell contains 2 of each chromosome, 1 from each parent
what is the haploid number?
(n) half the number of chromosomes that normal body cells have. gametes have a haploid number of chromosomes - 1 copy of each chromosome
why do gametes have a haploid number of chromosomes?
so when they combine they form a cell with the normal diploid number. half from each gamete
what does random fertilisation produce?
zygotes with different combinations of chromosomes to both parents. this mixing of genetic material in sexual reproduction increases genetic diversity within a species
what is meiosis?
a type of cell division that takes place in the reproductive organs. cells that divide by meiosis start as diploid and form haploid cells
what happens to DNA before meiosis starts?
DNA unravels and replicates so there are 2 copies of each chromosome, called chromatids
the DNA condenses to form double-armed chromosomes, each made from 2 sister chromatids joined in their centres by a centromere
what happens in meiosis I?
chromosomes arrange themselves into homologous pairs
these pairs are then separated, halving the chromosome number
2 haploid cells produced
what happens in meiosis II?
the pairs of sister chromatids that make up each chromosome are separated (centromere divided)
4 genetically different haploid cells (gametes) are produced
how many chromosomes do humans have?
46 chromosomes, 23 homologous pairs
what are homologous pairs of chromosomes?
chromosomes that are the same size and have the same genes (alleles).
1 chromosome in each pair came from mum and 1 from dad
what is meiosis needed for?
sexual reproduction, as it produces daughter cells with half the number of chromosomes of the parent cell
when is the chromosome number halved during meiosis?
chromosome number halved during the 1st division.
as sister chromatids are pulled apart in 2nd but each chromatid is still counted as a chromosome
what is chiasmata form?
during meiosis I, homologous pairs of chromosomes come together and pair up. the chromatids twist around each other and some alleles swap over.
the chromatids still have the same genes, just different combinations of alleles
what does the crossing over of chromatids mean?
each of the 4 daughter cells formed from meiosis contains chromatids with different alleles
what is independent segregation of chromosomes?
its completely random which chromosome from each pair ends up in which daughter cell when homologous pairs are separated.
so the 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
how are the outcomes of mitosis and meiosis different?
mitosis - produces cells with same number of chromosomes as parent
meiosis - half the number of chromosomes
mitosis - daughter cells are genetically identical
meiosis - daughter cells are genetically different
mitosis - 2 daughter cells produced
meiosis - produces 4 daughter cells
how are the processes of mitosis and meiosis different?
mitosis - only 1 division
meiosis - 2 divisions
mitosis - no pairing or separating of homologous chromosomes, so no crossing over or independent segregation of chromosomes
meiosis - does
what is chromosome mutation?
when the daughter cells produced in meiosis don’t have the correct number of chromosomes due to errors during meiosis
what do chromosome mutations lead to?
inherited conditions, because the errors are present in the gametes (hereditary cells)
what is non-disjunction?
a failure of the chromosomes to separate properly.
what can non-disjunction of chromosome 21 do?
in humans, non-disjunction of chromosome 21 during meiosis an lead to Down’s syndrome
what is Down’s syndrome caused by?
a person having an extra copy of chromosome 21.
this happens when that chromosome fails to separate properly during meiosis, so 1 cell gets an extra copy of 21 and another gets none
when this cell fuses with another gamete at fertilisation, the resulting zygote will have 3 copies of chromosome 21
what are the types of mutations of the DNA base sequence?
substitution deletion insertion duplication addition translocation
what is a substitution mutation?
one base is substituted with another
what is a deletion mutation?
one base is deleted
what does the order of DNA bases in a gene determine?
the order of amino acids in a particular protein
what does it mean that the genetic code is degenerate?
some amino acids are coded for by more than 1 DNA triplet
what effect does the genetic code being degenerate have on mutations?
not all substitution mutations will result in a change to the amino acid sequence of the protein
why are deletion mutations worse than substitutions?
deletion causes frameshift/ alters base sequence
changes sequence of amino acids
substitution alters 1 codon/ only 1 amino acid altered/ degenerate/ same amino coded for
what are mutagenic agents?
things that can cause an increase in the rate of mutations
what are some examples of mutagenic agents?
high energy radiation - UV radiation, X rays ionising particles - alpha, beta, gamma some chemicals some viruses carcinogens - mustard gas, phenols, tar
what is genetic diversity?
the number of different alleles of genes in a species or population
how is genetic diversity within a population increased?
mutations in the DNA - forming new alleles
gene flow
what is gene flow?
different alleles being introduced into a population when individuals from another population migrate into them and reproduce
what is a genetic bottleneck?
an event that causes a big reduction in a population.
how can a genetic bottleneck reduce diversity?
it reduces the number of different alleles in the gene pool, so reduces genetic diversity.
the survivors will reproduce and a larger population is created from a few individuals
what is an example of genetic bottlenecking reducing diversity?
northern elephant seals were hunted and the population was reduced to 50.
the population has built back up to 170000 but has a lot less genetic diversity than southern elephant seals which weren’t severely hunted
what is the founder effect?
its what happens when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool
how can the founder effect lead to a higher incidence of genetic disease?
the frequency of each allele in the new colony might be very different to the frequency of those alleles in the original population. e.g. an allele that was rare becomes common
what can cause the founder effect to occur?
migration leading to geographical separation or if a new colony is separated from the original population for another reason, such as religion
what is an example of the founder effect?
the Amish population all descended from a small number of swiss who migrated. they have little genetic diversity and few new alleles have been introduced. they have an unusually high incidence of certain genetic disorders
what is natural selection?
change in environment causes selection pressure
random mutations produce genetic diversity
some alleles provide an advantage to gaining resource
individuals with the alleles survive and reproduce
advantageous alleles are passed on
frequency of advantageous allele in population increases
frequency of trait increases
what are the different types of adaptations?
behavioural adaptations
physiological adaptations
anatomical adaptations
what are behavioural adaptations?
ways an organism acts that increase its chance of survival and reproduction. e.g. possums play dead if threatened by a predator
what are physiological adaptations?
processes inside an organism’s body that increase its chance of survival.
what are anatomical adaptations?
structural features of an organism’s body that increases its chance of survival.
what is an example of a physiological adaptations?
brown bears hibernate over winter. they lower their rate of metabolism, this conserves energy, so they don’t need to look for food
what is an example of an anatomical adaptation?
whales have a thick layer of blubber which helps them keep warm
what are the 2 types of natural selection?
stabilising selection
directional selection
what is directional selection?
where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
this could be due to an environmental change
what is an example of directional selection?
bacteria evolving antibiotic resistance
how does antibiotic resistance show directional selection?
some individuals in population have antibiotic resistant alleles
population exposed to antibiotic, killing non-resistant bacteria
resistant bacteria survive and reproduce, passing on allele
after time, most organisms in population will carry antibiotic resistance allele
what is 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, it reduces the range of possible characteristics
what is an example of stabilising selection?
human birth weight
how does human birth weight show stabilising selection?
very small babies are less likely to survive - can’t maintain body temperature
difficult to give birth to large babies, so less likely to survive
conditions are most favourable for medium-sized babies - so weights of babies tend to shift towards the middle of the range
what must you do when given information to interpret about an unfamiliar species?
describe what data shows
suggest a possible cause
how can the effects of antibiotics be investigated?
using agar plates
describe an investigating the effects of antibiotics practical:
bacteria from liquid broth are transferred to agar plate by sterile pipette and spread around plate using sterile plastic spreader
different antibiotic soaked pieces of paper placed on plate using sterile forceps, including control disk soaked in sterile water
lightly tape lid on, invert, incubate at 25*C for 48 hours.
similar techniques can be used for antiseptics and disinfectants
what is a liquid broth?
a mixture of distilled water, bacterial culture and nutrients. used to grow bacteria
what is an agar plate?
a petri dish containing agar jelly
what do the results of the investigating effects of antibiotics practical show?
bacteria grows forming a ‘lawn’ anywhere bacteria can’t grow is seen as a clear patch in lawn of bacteria, called inhibition zone
what does the size of an inhibition zone tell you?
it tells you how well an antibiotic works. the larger the zone, the more the bacteria were inhibited from growing
what are antiseptic techniques used for?
to prevent contamination of cultures by unwanted microorganisms.
why are antiseptic techniques important?
contamination can affect the growth of the microorganisms that you’re working with
contamination with disease-causing microbes could make you ill
what antiseptic techniques can be used in the investigating effects of antibiotics practical?
regularly disinfect work surfaces
don’t put utensils on work surface
place contaminated utensils in disinfectant
use sterile equipment and safely dispose after use
work near Bunsen burner
minimise time spent with lid off agar plate, to reduce airborne microorganisms contamination
briefly flame neck of broth container, before and after use
wash hands before and after
how is working near an Bunsen burner a antiseptic technique?
hot air rises, so any microbes in the air should be drawn away from your culture
what does flaming the necks of glass containers do?
causes air to move out of container, preventing unwanted organisms from falling in
what is phylogeny?
the study of the evolutionary history of groups of organisms. it tells us who’s related to whom and how closely related they are
what does a phylogenetic tree show?
all organisms have evolved from shared common ancestors. the tree shows the relationship between members of a family.
the 1st branch point represents a common ancestor of all family members.
each of the following branch points represents another common ancestor from which a different group diverged.
closely related species diverged away from each other most recently - their branches are close together
what is taxonomy?
the science of classification. it involves naming organisms and organising them into groups. this makes it easier to identify and study them.
what is a taxon?
there are 8 levels of groups used to classify organisms. these groups are called taxa. each group is called a taxon
what are the different taxa in order of size (largest first)?
domain kingdom phylum class order family genus species
how are taxa arranged?
in a hierarchy, with the largest groups at the top and smallest at the bottom. organisms can only belong to 1 group at each level. the more closely related the organisms the smaller the group they share
what are the 3 domains?
eukarya, bacteria and archaea
how many organisms does each taxa contain?
as you move down the hierarchy, there are more groups but fewer organisms in each group. there is only 1 type of organism in ‘species’
what is a species?
a group of similar organisms able to reproduce to give fertile offspring
what is the binomial system?
the nomenclature used for classification. all organisms are given 1 internationally accepted scientific name in Latin that has 2 parts
how are animals named according to the binomial system?
the 1st part of the name is the genus name and has a capital letter
the 2nd part is the species name and begins with a lower case letter
names are written in italics or underlined if handwritten
why is courtship behaviour used?
its carried out by organisms to attract a mate of the right species
what does it mean that courtship behaviour is species specific?
only members of the same species will do and respond to that behaviour. this allows members of the same species to recognise each other, preventing interbreeding and making reproduction more successful
how can courtship behaviour be used to classify organisms?
the more closely related species are, the more similar their courtship behaviour
what is the courtship behaviour of fireflies?
they give off pulses of light. the pattern of flashes is specific to each species
what is the courtship behaviour of crickets?
they make sounds that are similar to Morse code, the code being different for different species
what is the courtship behaviour of male peacocks?
they show off their colourful tails. this tail pattern is only found in peacocks
what is the courtship behaviour of male butterflies?
they use chemicals to attract females. only those of the correct species respond
what are 3 technologies that have been useful for classifying evolutionary relationships?
genome sequencing
comparing amino acid sequence
immunological comparisons
what is genome sequencing?
the entire base sequence of an organism’s DNA can be determined.
how can genome sequencing help to classify organisms?
the DNA base sequence of 1 organism can be compared to the base sequence of another organism, to see how closely related they are.
closely related species will have a higher percentage of similarity in their DNA base order
how can comparing amino acid sequence be used to classify organisms
the sequence of amino acids in a protein is coded for by the base sequence in DNA.
related organisms have similar DNA sequences so similar amino acid sequences in their proteins.
e.g. cytochrome can be used as it is present in many organisms
how can immunological comparisons be used to classify organisms?
similar proteins will also bind the same antibodies. so the more antibodies that bind to proteins in human blood that bind to proteins in another organisms blood, the ore similar the species
how were early estimates of genetic diversity made?
by looking at the frequency of measurable or observable characteristics in a population.
since different alleles determine different characteristics a wide variety of each characteristic in a population indicates a high number of different alleles - so high genetic diversity
how have new gene technologies been developed to help us measure genetic diversity?
different alleles of the same gene will have slightly different DNA base sequences. comparing the base sequences of the same gene in different organisms in a population allows scientists to find out how many alleles of that gene there are in that population
different alleles also produce slightly different mRNA base sequence, and may produce proteins with slightly different amino acid sequence, so these can also be compared
why are new technologies for measuring genetic diversity important?
used to give more accurate estimates of genetic diversity within a population or species.
allow the genetic diversity of different species to be compared more easily
what is variation?
the difference that exists between individuals. there’s variation between species and within species
what can cause variation within a species?
genetic factors
environmental differences
most variation within a species is caused by a combination of these
how can genetic factors cause variation between species?
different species have different genes, which causes variation between species. they may also have a different number of chromosomes
they can’t breed to produce fertile offspring and have different features
how can genetic factors cause variation within a species?
individuals of the same species have the same genes, but different alleles
why do we only look at a sample of the population when investigating variation?
for most species it would be too time-consuming or impossible to catch all the individuals in the group. so samples are used as models for the whole population
what must be done when using a sample to model a population?
make sure its an accurate representation
any patterns observed are tested to make sure they’re not due to chance
how can you make sure the sample isn’t biased?
it should be random. e.g. draw grid over a map of the land generate coordinates using random number generator place quadrant at coordinates use same sized quadrant each time
how can variation in a sample be proven to not be down to chance?
to make sure any variation observed in the sample isn’t due to chance,
increase sample size
analyse the results statistically.
this allows you to be more confident that the results are true and reflect what’s happening in the whole population
what is a normal distribution?
a bell-shaped graph, which has a peak at the mean and is symmetrical about the mean, with values on either side
what is standard deviation?
how much the values in a single sample vary. its a measure of the spread of values about the mean
what do different sized standard deviation mean?
large s.d. means the values in the sample vary a lot.
small s.d. means most of the sample data is around the mean value, so varies little
what are error bars?
how standard deviations are plotted on a graph. with 1 s.d. above and below the mean
the longer the bar, the larger the s.d. and the more spread out the sample data is from the mean
what is biodiversity?
the variety of living organisms in an area
what is a habitat?
the place where an organism lives
what is a community?
all the populations of different species in a habitat
what is local biodiversity?
the variety of different species living in a small habitat thats local to you
what is global biodiversity?
the variety of species on earth. recent estimates put the total number of species on earth at about 8.7 million. biodiversity varies in different parts of the world - greatest at the equator , decreases at the poles
what is species richness?
a measure of the number of different species in a community. it can be found by taking random samples of a community and counting the number of different species
why isn’t species richness a good measure of biodiversity?
the number of different species in a community isn’t the only thing that affects biodiversity, population sizes of the species do too
what is an index of diversity?
a way of measuring biodiversity that takes into account the population sizes of species as well as the number of species.
the higher the number the more diverse an area is
what is the formula for an index of diversity?
Σ n(n-1)
N = total number of species of all species
n = total number of organisms of 1 species
what methods do farmers use to maximise the amount of food they produce that reduce biodiversity?
woodland clearance hedgerow removal pesticides herbicides monoculture
why is woodland clearance used?
done to increase the area of farmland.
directly reduces number of trees and sometimes number of different species of trees.
destroys habitats, so can reduce species’ shelter and food sources. species will die or migrate, reducing biodiversity
why is hedgerow removal used?
increases area of farmland by turning lots of small fields into fewer large fields.
reduces biodiversity by removing habitats, reducing variety of food and shelters so reducing variety of organisms that need them
what are pesticides?
chemicals that kill organisms that feed on crops.
reduces diversity by directly killing the pests.
any species that feed on the pests lose a food source, so their numbers decrease too
what are herbicides?
chemicals that kill unwanted plants.
reduces plant diversity and could reduce the number of organisms that feed on the weeds
what is monoculture?
when farmers have fields containing only 1 type of plant. a single type of plant reduces biodiversity directly and will support fewer organisms, which reduces biodiversity
what are some examples of conservation schemes?
giving legal protection to endangered species
creating protected areas such as SSSIs and AONBs that restrict further development, including agricultural development
the environmental stewardship scheme
what are SSSIs?
sites of special scientific interest
what are AONBs?
areas of outstanding natural beauty
what is the environmental stewardship scheme?
it encourages farmers to conserve biodiversity e.g. by replanting hedgerows and leaving margins around fields for wild flowers to grow
what happens in interphase before meiosis?
cell growth, DNA replication, more organelles
what happens in prophase in meiosis?
nuclear envelope breaks down, spindles form, chromosome condense, homologous chromosomes pair up (bivalents), crossing over and recombination of alleles (chiasmata form)
what happens in metaphase in meiosis?
metaphase I - homologous pairs line up at middle of cell via spindle fibres
metaphase II - chromosomes (in sister chromatid pairs) line up at middle of cell via spindle fibres
what happens in anaphase in meiosis?
anaphase I - homologous pairs are pulled to opposite sides of cell by spindle
anaphase II - sister chromatids are pulled to opposite sides of cell by spindle
what happens in telophase in meiosis?
2 nuclear envelopes form
meiosis exam technique:
homologous chromosomes pair up chiasmata form produce new combination of alleles chromosomes separate (segregate) at random (random segregation) produce varying combination of chromosomes chromatids separation at meiosis II
what is a mutation?
random change in base/nucleotide sequence of DNA
more likely to occur during interphase because this is when DNA replication/ synthesis occurs
how can a mutation lead to the production of a non-functional enzyme?
change in base/ nucleotide sequence of DNA/ gene
change in amino acid sequence/ primary structure
change in hydrogen/ ionic/ disulfide bonds
change in tertiary structure
change in active site
no enzyme-substrate complexes form
how does a deletion mutation alter alter the structure of a gene?
removal of 1 or more bases/ nucleotides
frameshift / base sequence change
how could a mutation lead to a protein with a missing amino acid?
loss of 3 bases/ codon
triplet for last amino acid is changed to a stop codon
how many possible combinations of chromosomes in a gamete are there?
2^n
n= the number of pairs of homologous chromosomes
how many possible combinations of chromosomes are there after gametes fuse?
(2^n)^2
what is a population?
a group of the same species, in the same place, that can interbreed
why is genetic diversity advantageous?
more genetic diversity = more alleles
wider range of characteristics/ variation (bigger gene pool)
greater chance of individuals surviving environmental change
what is selection?
the process by which organisms that are better adapted to their environment survive and reproduce, while those less well adapted do not
what is a selection pressure?
an environmental change that leads to selection
what are the different types of variation?
continuous variation
discontinuous variation
what is continuous variation?
a characteristic that can have a wide range of values shows continuous variation.
a histogram of continuous variation in a population produces a ‘bell shaped’ normal distribution curve
what is discontinuous variation?
a characteristic with few possible values shows discontinuous variation
there are a few discrete categories
what does courtship behaviour allow individuals to do?
recognise members of the same species
identify a sexually mature mate
form a pair bond that will lead to successful mating and raising of offspring
synchronise mating so that it takes place at a time where egg and sperm are likely to meet
become able to breed by bringing a member of the opposite sex into a state that allows breeding to occur
what is artificial classification?
grouping organisms based on features that are useful at the time e.g. colour.
the evolutionary origin of these features may not be taken into account
what is phylogenetic classification?
based on evolutionary relationships
determined from fossils, DNA and analysis
based on shared ‘homologous’ features derived from their evolutionary ancestors
arrange organisms into groups called hierarchies, which are groups within groups that don’t overlap
what is an ecosystem?
a community of organisms and the habitats in which they live
what is a natural ecosystem?
an ecosystem that develops over time and form complex communities with huge biodiversity
what are artificial ecosystems?
controlled by humans
have low genetic diversity, species richness and index diversity
e.g. agricultural ecosystems - farmers select which species are allowed to grow
what impact do artificial ecosystems have on biodiversity?
by reducing competition, few species dominate genetic diversity decreases species richness decreases index of diversity decreases fewer habitats variety of plants/insects decreases variety of niches decreases
what is species diversity?
the number of different species and the number of individuals of each species within any 1 community
what is ecosystem diversity?
the range of different habitats, from a small local habitat to the whole of the earth
how can evolutionary relationships be determined? (best to worst)
compare DNA sequences compare mRNA sequences compare amino acid sequence compare proteins/ enzymes compare physical characteristics
how can we compare the DNA sequences of different species to classify them?
we can read the DNA sequence of any organism to determine the exact order of nucleotide bases.
this is automated using machines
each base is tagged with a colour, this produces a ‘heat map’ which can be easily compared
organisms accumulate random mutations over time, more closely related species show more DNA similarities
how can we compare mRNA sequences of different species to classify them?
mRNA is coded for by DNA
mRNA is complementary to the DNA from which it is transcribed
so species who share similar mRNA sequences are more closely related
how to find average leaf width of an individual plant unbiasedly?
number leaves
place numbered balls in a bag
select balls at random
measure width of corresponding leaves and find average
