UNIT 4, Topic 4A & 4B - DNA, Protein Synthesis, Diversity, and Classification Flashcards
(151 cards)
1
Q
a gene occupies…
A
a fixed position called a locus on a particular DNA molecule
2
Q
gene
A
A gene is a base sequence of DNA that codes for : amino acid sequence of a polypeptide, and, a functional RNA (including ribosomal RNA and tRNA)
3
Q
functional RNA
A
Functional RNAs areRNA molecules that are not translated into proteins.
This includes tRNA and rRNA.
NOT mRNA (info is turned into a protein): and tRNA is included as functional because it’s a carrier only.
4
Q
ribosomal RNA
A
Ribosomal RNA arethe subunits on a ribosome. They associate with a set of proteins to form ribosomes.
Ribosomes are the organelles where proteins are formed in a cell. It consists of a large and small subunit that is made up of ribosomal RNA (rRNA).
5
Q
DNA
A
A chemical polymer (polynucleotide) that stores genetic information for a cell
6
Q
loci
A
a fixed position a gene occupies on a chromosome
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Q
allele
A
alternative form of a gene (in the same loci and chromosome) that’s caused by random mutations mostly
8
Q
codon
A
3 mRNA molecules/ 3 adjacent bases
“3 bases code for one amino acid”
9
Q
primary structure of protein…
A
the UNIQUE sequence of amino acids
10
Q
genome
A
the complete set of genes / genetic make up in a cell
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Q
proteome
A
the entire set of proteins expressed by a genome: all the proteins a cell is able to code for
- use this phrasing as not all proteins can or are made at the same given time
12
Q
give 3 features of eukaryotic DNA
A
- linear (and enclosed in a nucleus)
- long
- bundled into chromosomes
- contains histones (proteins)
13
Q
Give 3 features of prokaryotic DNA
A
- short
- circular DNA (plasmids)
- does not contain/ associated with proteins (histones)
- found in the cytoplasm (no nucleus)
14
Q
histones
A
The protein that DNA molecule wraps around, also provides structural support for a chromosome
15
Q
introns
A
sections of a gene that are not expressed in final RNA products (aka dont code for amino acids)
16
Q
exons
A
coding regions of a gene that code for a protein / amino acid sequence (they are the reason for splicing)
17
Q
what is the genetic code?
what’s a triplet code?
A
Described as a sequence of bases (adenine, guanine, cytosine, thymine) which, when arranged in a certain order, code for specific amino acids.
A triplet code describes how an amino acid is coded for by a group of 3 bases.
(note that codons actually code for an amino acid during transcription, hence the codon table. The tRNA, anticodon, is just essentially used as a carrier for the amino acid because it’s complementary to the mRNA’s codon)
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Q
What determines the sequence of amino acids?
A
the order of bases to form a polypeptide (each with a different amino acid sequence).
19
Q
after the primary structure, how does the tertiary structure help define the protein / polypeptide chain?
A
Hydrogen, ionic, and disulfide bonds form between the R groups on the amino acid causing the chain to fold further and form a protein, and this gives it its function, such as an enzyme
20
Q
why do different species have different base sequences?
A
(mutations)
In terms of proteins, they need different Gene’s to be able to make different proteins
21
Q
read…
A
correct order:
1. DNA base sequence codes for…
2. (after transcription and translation) amino acid sequence determines…
3. polypeptide chain determines…
4. (after folding) protein structure and function
22
Q
practice some Exam Qs
A
.
23
Q
bonds in polypeptide chain
A
peptide
24
Q
3 code words used to describe DNA
A
degenerate, universal, non-overlapping
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degenerate code
why is this advantageous?
Several base triplets can code for the same amino acid.
- e.g. only 20 amino acids but 64 possible combinations of triplets
Its advantageous as despite mutations, theres a chance that the mutation won't have an affect in the amino acid coded for in the end
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non-overlapping code
Each base in sequence is read only once!
So the base cytosine in ATC, for example, would not be read twice for the next triplet
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read
DNA: triplet
mRNA: codon
tRNA: anticodon
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universal code
- what does this suggest about evolution?
the same specific base triplets code for the *same amino acids* - in all living things.
- Suggesting we all have a common ancestor.
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heterozygous
(might not be on spec)
non identical alleles
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Extra features of eukaryotic DNA
1. wrapped around histones
2. mitochondria and chloroplasts have their own DNA
3. most DNA doesn't code for polypeptides
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What are the 2 purposes of histones
1. Allows large DNA molecule to be stored compact by wounding the linear DNA around it. Then, associated proteins and DNA are coupled up tightly to form a chromosome
2. They help support the DNA
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Describe the DNA found in mitochondria and chloroplasts (organelles only have their own DNA in eukaryotic cells)
It's similar to prokaryotic: short, circular, and not associated with proteins. (can link to suggests commona ancestor)
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Explain why most DNA in eukaryotes doesn't code for polypeptides
some genes code for functional RNA instead of polypeptides (which is also ribosomal and tRNA).
Additionally, the genes that do code for polypeptides contain non-coding regions as well as coding (introns, multiple repeats and exons).
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Multiple repeats?
These are regions in eukaryotic DNA base sequences that occur outside of Gene's. They repeat many times but do not code for amino acids.
- non-coding repeats
e.g. CGCGCGCGCGCG and you would describe this repeating sequence of GC to be 12 bases long.
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in the definition of a gene you dont have to include...
the fact exons and introns exist
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2 types of non coding DNA
non- coding/ multiple repeats and introns
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genome
the complete set of genes in a cell.
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proteome
full range of proteins that the cell can code for / produce
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what's the link between the genome and proteome?
Proteome is as a result of the full genome; as it contains genes that code for specific proteins.
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protein synthesis definition, and define translation and transcription
The production of polypeptides (that fold to form proteins) within the cell using the genetic code, 2 parts: transcription and translation.
Transcription: the production of mRNA from DNA (different in prokaryotes and eukaryotes)
Translation: the production of polypeptides from the sequences of codons carried by mRNA.
- DNA and RNA are involved in these stages
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what are the 3 different terms used to describe a group of 3 bases
triplet, codon and anticodon
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What are the 4 causes of genetic variation?
1. a change in DNA base sequence (gene mutation)
2. meiosis: independent segregation of homologous chromosomes and crossing over
3. chromosomal mutations (non-disjunction)
4. random fertilisation of gametes
extra : migration
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where do gene mutations come from?
arise spontaneously in DNA replication (base deletion, substitution...)
AND due to degenerate nature of the genetic code, not all substitutions cause a change in the encoded sequence of amino acids
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what can increase the rate of gene mutations?
mutagenic agents
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types of gene mutations
duplication, addition, translocation, substitutions, deletion
- these happen on DNA base sequences that also change the mRNA sequence (reading carefully on questions which molecule the mutation is impacting - mock Q)
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example of mutagenic agents
carcinogenics (such as from sun damage/ overexposure to UV)
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Why do you think gene mutations arise during interphase?
Stage includes replication:
this is when the bases are exposed and not protected by the DNA double helix structure or any bonds and so are vulnerable
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which type of 3 bases is affected by mutations, such as substitution?
Triplets
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Exam Q feedback:
Q: a mutation can lead to the production of a non-functional enzyme, explain.
Missed a mark for not stating the names of the bonds in the tertiary srructure
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Suggest what deletion mutations have a worse impact than substitution mutations.
(using info from Q)
Substitution makes TGC be coded for TAC instead, only affecting one triplet.
Deletion makes a frameshift; shifts entire sequence changing almost every each amino acid coded for as triplets have shifted (using info again) and this is worse due to the non-overlapping nature where triplets are read in 3s and the same base of a triplet is not read twice.
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2 amino acids sequences had experienced substitution mutations, only one was affected.
Explain why (for both)
1st substitution was harmless and had no impact on the amino acid sequence due to the degenerate code.
2nd changed an amino acid in the sequence which could alter the protein structure and potentially making it non-functional ...
(only if that change happens to be in the active site of a tertiary structure of an ENZYME or is an amino acid that's involved in forming bonds such as ionic, hydrogen or sulfide bridges for example)
- 2 questions in one
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Where does meiosis occur?
in reproductive organs (mostly)
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purpose of meiosis
to produce haploid cells called gametes
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reason for having haploid daughter cells, importance, and what would happen if meiosis didn't occur?
to maintain chromosome number of species the same, necessary
- gametes would have the normal number of chromosomes in a haploid cell, causing the zygote after fertilisation to contain the incorrect amount of chromosmes
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daughter calls number in meiosis
4
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purpose of meiosis?
producing sex gametes with genetic variation that MAY later be used in sexual reproduction to create a zygote (new life)
when you see 2n on a diagram go to just n.
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purpose of mitosis?
cloning body cells for growth and repair
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What's supercoiling?
Prokaryotes also carry DNA molecules as chromosomes but shorter and circular.
Since there are no histones to be wound around, it condenses to fit into the cell by supercoiling itself.
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structure of tRNA and function?
1. Amino acid binding site on opposite end of anticodon, clover shape as tertiary structure with complementary hydrogen bonds.
2. Anticodon binds to complementary codon eventually (ATP involved) and translation occurs. It carries correct amino acid in correct order from cytoplasm to MRNA chain.
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The result of transcription differs from eukaryotes to prokaryotes, explain.
Eukaryotes: results in pre-mRNA (which is an exact copy of a gene of the DNA) , this is then spliced to form MRNA.
Prokaryotes: results directly in the production of MRNA from DNA.
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role of translation
to produce a polypeptide from the sequence of codons carried by MRNA.
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Protein synthesis
Check drawn notes
.
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Where does splicing occur?
In nucleus before (mature) mRNA moves to ribosome for translation
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Splicing is where...
pre mRNA have their introns removed, and the tendons are spliced together, because they are the parts of the copied gene that code for the protein.
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Non-coding DNA includes...
introns and multiple repeats
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where have the amino acids in the cytoplasm come from?
digestive system: hydrolysed proteins into sub units of amino acids
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where have the amino acids in the cytoplasm come from?
digestive system: hydrolysed proteins into sub units of amino acids
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what must exist on the DNA for RNA polymerase to be able to attach?
complementary binding site for RNA polymerase's active site
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when does crossing over occur?
homologous pairs of chromosomes cross over just before the first meiosis division
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describe random fertilisation
After sexual reproduction, the gametes of 2 unrelated individuals may fuse together to produce a genetically varied diploid cell, called a zygote.
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describe what independent segregation of homologous chromosomes is
When the homologous pairs are separated, its random which chromosomes from each path ends up in which daughter cell.
- and ofc there are many pairs in the whole haploid cell.
Resulting in the 4 daughter cells to have completely different combinations of the same chromosome (or gene) through meiosis.
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what does crossing over result in?
In the sister chromatids of the homologous pair having new combinations of alleles at a given section of the chromatid (same gene and loci!)
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chiasmata
the point of breakage where the DNA breaks and is exchanged, so non - sister chromatids have different combinations of alleles
(same gene and loci)
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How does crossing over contribute to genetic variation? (3)
1. At chiasmata....
2. Mention of different allele combos BUT the same gene and loci
3. ...results in non-sister chromatids having some new combinations of alleles
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What is independent segregation of homologous chromosomes and how does it lead to genetic diversity?
- Which side the chromosomes of the homologous pairs take, how they choose to independently align themselves.
" It's completely random which chromosome from each pair ends up in which daughter cell. This leads to 4 cells having different combos of a person's maternal/ paternal chromosomes. This increases genetic diversing
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How to calculate the number of possible chromosome combos for each gamete?
2^n
where n is the pairs of homologous chromosomes of the organism
and for zygote 2^n × 2^n
- new combos of alleles
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27 chromosomes: haploid or diploid?
Diploid has 2 sets of chromosomes hence must have an even number, so haploid
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why is the creation of eggs and sperm in some organisms not meiosis?
it may just be mitosis, it's only meiosis when you see 2n turn into n, halving chromosome numbers, common example plants
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2 events during meiosis (excluding the process itself as a whole, aka more detail) that increase genetic variation.
crossing over, independent segregation of homologous chromosomes
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zygote
fused gametes after fertilisation
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In plants, what's a gametophyte and a sporophoyte?
G: produces gametes sexually (involves mitosis in plants, extra info)
S: produces spores asexually
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Does meiosis produce gametes?
Yes but not always in other organisms
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diploid
Containing 2 complete sets of chromosomes, one from each of the person's parents.
So n = a complete set of chromosomes
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Non - disjunction
When (a pair) of chromosomes fails to separate, leading to an incorrect number of chromosomes in daughter cells.
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Example of non-disjunction
An example of chromosome mutation is Down’s syndrome: Individuals with this syndrome have a total of 47 chromosomes in their genome as they have three copies of chromosome 21.
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what are chromosome mutations caused by ?
errors in meiosis (e.g. non- disjunction or even polyploidy where there are more than 2 complete sets of chromosomes.
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how can a gene sequence mutation of substitution result in the same amino acid sequence.
- substitution of one triplet into another (state)
- causes no change if both code for same a. acid
- degenerate code
- sequence remains unharmed, same chain coded for
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index of diversity formula
d = N(N-1) / En(n-1)
N: total number of organisms, all species
n: total number of organisms of each species
E: sum of
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species
similar individuals that can mate to produce fertile offspring
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habitat
where species is usually found
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population and community definition
1. total number of organisms of the same species in a particular area
2. a range of species in an area that co-exist
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Whys it important to have high biodiversity (in a range of scales)?
Different organisms offer a variety of more food sources and habitats for other organisms of species to use; you would phrase this as an increase in ecosystem productivity
- also increase in ecosystem stability as it helps mitigate changes.
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Species richness
A measure of biodiversity: the number of different species in a community.
- rainforest would have high species richness (due to more habitats, niches, water and a wide range of food sources) - all about variety.
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what is the index of diversity?
A measure of biodiversity that takes into account number of species in a community (so species richness) AND the number of individuals in each species (population size).
- this index for it is also more useful than species richness because it takes into account species measured in small numbers and equally weighs communities with different population sizes of species.
(From exam Q, mention any patterns from data)
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Can a fair comparison of biodiversity of 2 habitats be made without considering all individuals of each species?
No. Even though species richness may be the same, it's important to note the proportions of the individuals in each.
- there may be an imbalance you'd not be aware of, such as if theres a dominant species.
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what does a higher index of diversity indicate?
a higher biodiversity, which is good
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what is meant by species diversity? (note included)
The amount of different species in an area and the number of individual in each species (so the proportion of each)
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Biodiversity
A range of habitats and species (proportions too)
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Monoculture
Area with only one species, e.g. farming wheat
- affects sustainability of ecosystems, less food sources and variety of habitats to provide for many species now and in future times
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Farming techniques and vague impacts.
Deforestation
Hedgerow removal
Mowing,harvesting
Planting monocultures
Herb/ Pesticides
(Selective breeding)
- negative multiplier effect of decreased diversity
- soil erosion
- removing smaller communities w the hedgerows
- contaminating water
- air pollution if burning trees
etc.
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Conservation measures to farming techniques
Do some exam Qs on this or read notes on save my exams
- organic farming, no chemicals
- allow wildlife corridors
- protected sites for scientific interest or natural beauty
etc
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ways removing hedges may benefit farmers to increase crop yields
- less animals/ insects feeding on them
- larger field = more crop
- more efficient as hedges compete for resources like water, space
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ways hedges could help increase crop yields long term
- nutrients from dead organisms in soil can be absorbed by crops
- hedges decrease soil erosion and increase pollinators along the corridors
- hedges - several species due to feed and habitat : hence, insects are natural protection against some pests (e.g. lady birds eat aphids)
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Benefit of converting land for food purposes despite decrease of biodiversity and less species surviving
Cheaper food production
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name all types of mutations
deletion, substitution, translocation, insertion, duplication, chromosome mutation
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Taxonomic classification hierarchy of order
Domain, kingdom, phylum, class, order, family, genus, species
- Delightful king penguins climb over frozen, grassy slopes
- More groups within taxas as you go down the levels, and they change sometimes due to new species discoveries
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hierarchy
Largest group at top, groups subdivided into smaller with no overlap.
(Organisms belong to one group in each taxa, and organisms in the same group at each level are closely related,especially the further down you go)
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Naming species?
Bionomial name
Italics, genus species, no capital for species
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Phylogeny and phylogenetic groups
The study of evolutionary history of groups. Shows who is related to whom, and how closely related : theory states evolved from one common ancestor.
- groups arranged into a hierarchy (groups within groups, no overlap)
- evolutionary relations between organisms and ancestors
- classifies species into groups ; shared features from ancestors.
MUST mention all 3 characteristics.
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Phylogenetic diagram notes
Each branch point represents a common ancestor to all the following organisms linked to that branch.
Any branch points after that / further along show more recent common ancestors from which a group has split (sharing a more recent common ancestor)
- see pictures online.
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Intra breeding
Breeding between the same species
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Inter breeding
Breeding with other species
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Product of interbreeding
Hybrid organism,usualy infertile due to uneven diploid number
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what's the key term that describes the way species ensure they are intra breeding? And what is the definition? (including an important phrase)
Courtship behaviour, specific to each species (only they RESPOND).
" Precursor for mating "
- It allows species to recognise each other and makes reproduction more successful because (!) fertile offspring produced and alleles passed to next gen... species unlikely to go extinct.
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why courtship behaviour is important and examples of behaviours.
- ensure same species, stop interbreeding, ensure successful reproduction for fertile offspring lavoiding extinction), identify sexually mature mate (e.g. egg producing), and to forma pair bond sometimes to raise offspring.
examples: vocalising, visual display, building, dancing, chemical / pheromone release.
- some of these take effort or prove they would be a good mate: shows how important it is.
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genetic diversity
number of *different* alleles of genes within a species / population, so having a large (gene) pool of different alleles.
- a factor enabling natural selection to occur and for populations to then evolve
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how to tell if 2 organisms belong to the same species (not courtship related)
similar DNA base sequence and amino acid sequences in proteins, the more closely related they are (and have fertile offspring for the same sequence).
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genome
full set of genes in the DNA / genetic material of a cell
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Explain how advanced in genome sequencing clarify evolutionary relationships
Entire DNA base sequences of organisms can be determined: then compared to see how closely related.
We can sample DNA and use tech to display it better with patterns (each nucleotide has a specific dye) to see similarities across the board, and there will be more differences to less closely related BECAUSE OVER TIME MUTATIONS HAPPEN.
- questions will usually come up in the format of % of similarity in base sequence or given the base sequence itself and you have to make that judgement.
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Comparison of mRNA base sequence (link to advancements to clarify evolutionary relationships): read note.
mRNA base sequence is complementary to DNA strand it was made from; we can measure DNA and genetic diversity by comparing these mRNA sequences .
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How do comparing amino acid sequences of proteins clarify evolutionary relationships?
Sequence DETERMINED by mRNA, which determined by DNA, so genetic diversity within and between species can be compared.
Similarities reflect how closely related - can be done by counting similarities or differences.
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How immunological comparisons can clarify evolutionary relationships
Similar proteins will bind to similar antibodies.
- any protein that is similar to a different species proteins will be recognised by their antibodies.
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What are observable characteristics (sort of linked to evolutionary relationships)
physicality, which alone, has its limitations
- using technology allows you to compare the genes associated with the characteristics.
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Artificial classification
based on morphology (physicality and their functions)
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intraspecific variation (opposite to inter)
variation among the same species
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phylogenetic group
grouped according to evolutionary links
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how might a mutation be positive?
Many are harmful, but in some environments, new allele of a gene may benefit its possessor, leading to increased reproductive success.
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gene pool
A small or big combo of alleles in a reproducing population at a specific time ( ^ diversity)
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why is genetic diversity/ large gene pool important?
Helps a species survive if environment changes, so with this there is more likely to be a wider range of characteristics and so ^ probability individuals may posses characteristics that suit new conditions, avoiding extinction.
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gene flow
individuals from a population migrating into another population & reproducing - alleles can flow between populations and impact gene pool size.
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What are some features determined by in organisms?
some by proteins
- linking to how different DNA = different appearance = showing ^ genetic diversity.
- DNA to MRNA to amino acid sequence to different shaped proteins and levels of structure, altering appearance and creating genetic diversity.
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2 ways genetic diversity is decreased?
founder and bottleneck effects
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Describe how genetic bottleneck effect decreases genetic diversity
- Where a dramatic decline in population of species occurs before they reproduce (for at least one generation) IMPORTANT TO MENTION
- There are few survivors so the number of different alleles in the gene pool decreases: limited allele diversity.
- When few survivors reproduce, a new population is created from a small number of individuals (some alleles may have been lost before they had a chance to reproduce to pass the alleles on!!!)
--- in an exam Q consider mentioning surviving population and the difference in frequency in alleles (mention reproduction).
- happens due to an event: chance, humans or natural disaster.
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Describe how the founder effect reduces genetic diversity
- where a few individuals from the population move to a new region and start a new colony; or are individuals are selected and separated (fastest chickens, e.g.)
- only a small fraction of the range of alleles from the original population contribute to this gene pool so genetic diversity is reduced
- when reproducing a new population, there is limited genetic diversity compared to before
- inbreeding within the colony (the Amish) make alleles more common
135
Apart from genetic factors, what other type of factor causes variation within a species?
environmental
136
What are the 2 types of natural selection? Give examples (must know).
Stabilising selection: birth weight
Directional selection: antibiotic resistance
Both affect allele frequency
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Natural selection
- can only happen if there are multiple or diversity of alleles
When species become better adapted to their environment (as some phenotypes are preferred) AND PASS ON BENEFICIAL ALLELES (leads to evolution)
(types of adaptations - anatomical, physiological, behavioural)
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Selection pressures
Determines successful traits. Pressures: climate, food sources, habitat, PREDATORS > some individuals have more of advantage over others, hence the selection
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Evolution
A change in allele frequency over many generations in a population
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Natural selection occuring (4 point genetic answer model)
- within any population of a species there will be a gene pool containing a wider variety of alleles.
1. Random mutations can result in new alleles of the gene and therefore is a variation.
2. In certain environments, the new alleles of a gene may benefit its possessor so it can survive (over others), leading to an increased reproductive success.
3. This advantageous allele is inherited by members of the next generation.
4. Over many generations, the new alleles increases in frequency in the new large population.
- ensure you're making it so it is applied to the question with a specific answer
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What is normal distribution?
The frequency of any phenotype in a population that can be shown graphically and is usually a bell shape curve.
- sliding scale where the most common is in the middle (highest frequency)
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Describe characteristics of stabilising selection and when it happens.
- organisms with phenotypes closest to mean are more likely to survive, reproduce and pass on beneficial alleles.
- it happens when environmental conditions aren't changing AND THE MEAN (middle) VALUE STAYS THE SAME, but frequency of the mean value increases.
(curve becomes narrower and taller)
(!) The range of possible phenotypes is small as extreme phenotypes are selected against and so the phenotypes closest to the mean are favoured.
- baby birth weight is an example
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Describe the characteristics of directional selection and when it happens
- where individuals with a phenotype at one of the extremes are more likely to survive, reproduce and pass on their beneficial alleles. " EXTREME IS FAVOURED, so population with this characteristic increases - talk about mean "
- this could happen in response to environmental changes. And so characteristics shift towards another one.
- the mean value changes (as there's more individuals with a extreme phenotype) in one direction or the other as it shifts, but the frequency remains the same.
- antibiotic resistance is an example, curve moves further towards higher levels of antibiotic resistance, the environmental change here is antibiotics and so is a selective pressure that favours resistant bac.
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What is selection?
When organisms become better adapted to their environment (increasing frequency of some alleles due to mutations) and so are more likely to survive, reproduce and pass of beneficial alleles.
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factors increasing rate of mutations
mutagens
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Without adaptation and selection the diversity of living organisms would decrease and evolution would stop. Explain Thai statement.
1. Because there would be no random mutations, causing a lack of varying new alleles and no extreme characteristics - no adaptation to changing environment.
2. Some members then can't benefit from any advantageous alleles to keep them alive and reproduce (and so survival rate decreased if change in environment).
3. So no advantageous alleles inherited by next generation's offsprings.
4. So no increase in (advantageous) allele frequency in population so no changes or natural selection will occur to drive evolutionary change.
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What are behavioural adaptations? Give an example
When organisms start behaving different to increase their chances of survival and pass on their alleles to offspring. Change in response to external stimulus.
- like possums playing dead
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What are physiological adaptations? Give an example
When internal chemicals or processes change (like the regulation of homoeostasis), happens in organs and cells.
Such as fish releasing antifreeze proteins to avoid freezing in cold temperatures or in hibernation where bears lower their metabolic rate to conserve energy
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What are anatomical adaptations? Give an example
Physical change to an organism's structure or phenotype ton in rear chance of survival.
Like polar bears being white to camouflage in environment
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Explain why the following equipment or aseptic techniques are used in experiment of: the effect of antimicrobial substances on microbial growth.
1. Agar plates
2. Serial dilution
3. Flaming the neck of the bottle
4. Lifting the agar lid at an angle.
1. Solid nutrient broths for bacterial growth containing water, minerals/ vitamins, glucose etc. for respiration and energy for growth (example)
2. Diluting a bacteria culture to ensure there's not an overwhelming and dangerous amount of bac. in broth culture so easier to control.
3. Kills any unknown bac. near neck to avoid mixing and contamination and sweeps away any bac in air through convection currents.
4. Minimal exposure to contaminations and so decreases this likelihood. Opening it just enough to carry out procedures and for a minimal time.
And can also stop tested bacteria from getting out!
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zone of inhibition
area around disk where bacterial growth has been inhibited and bac have been killed, tells you the efficiency of a substance at killing a certain type of bacteria
