genetic info & variation Flashcards
structure of DNA (4)
- double stranded
- each strand is a polynucleotide made up of individual nucleotides
- each nucleotide contains phosphate, deoxyribose, and nitrogenous base
- A with T, C with G
where is DNA found(3)
-prokaryotic cells have a single molecule of DNA ,some have plasmids,DNA not associated with proteins
DNA in chloroplasts and mitochondria is short, circular and not associated with proteins
-DNA in nuclei of eukaryotes is long, linear, associate with histone proteins, form a chromosome
Chromosome (3)
- DNA molecule wrapped around a histone, complex coiled into solenoid and then further coiled, very long DNA condensed, lots of genetic info stored
- In interphase chromosomes are dispersed throughout the nucleus
- diploid organisms inherit a full set of chromosomes from each parent, , have homologous pairs of chromosomes
what is a gene?(5)
- a base sequence of DNA that codes for either amino acid sequence of a polypeptide or a functional RNA
- gene occupies a fixed position called a locus
- DNA has many genes
- most of DNA molecule in humans doesn’t code for amino acid sequence, it is non coding
- exons code for amino acid, non-coding is introns
define genome
the complete set of all of the genes in a cell, including the genes in the nucleus, mitcochondria and chloroplasts
define proteome
the full range of all the proteins that a cell is able to produce using its genome
define allele
some genes have two or more alternative forms, each allele has a different sequence of bases so codes for a different polypeptide
define gene pool
all the different alleles of all the genes found within a population
define degenerate
there is more than one set of three bases that codes for each amino acid
define non overlapping
each base is only part of one triplet, it is only read once
define universal
the same three bases code for the same amino acid in all organisms
the genetic code
5
- every three bases is a triplet and codes for a specific amino acid
- 64 possible combinations for 20 amino acids
- code is degenerate, universal and non overlapping
- first triplet is always methionine
- three stop triplets
types of RNA
Structure
- two types are needed to synthesise proteins , mRNA and tRNA
- RNA is a single stranded polynucleotide, contains phosphate, ribose, AUCorG
messenger RNA (3)
- few thousand nucleotides long
- bases don’t bond to each other
- three bases is called a codon
transfer RNA
6
- about 75 nucleotides long
- strand folds back on itself to form a clover shape and hydrogen bonds form between complimentary base pairs
- amino acid binding site at the end of the molecule
- three exposed bases= anticodon
- 61 types of tRNA which each carry a specific amino acid
- anticodon binds to a complimentary codon on mRNA in translation
Transcription
RNA polymerase binds to the coding sequence
DNA unwinds and Hydrogen bonds are separated
RNA nucleotides base pair on the template strand
RNA polymerase catalyses the formation of bonds between RNA nucleotides to form mRNA transcript
When end of base sequence is reached RNA polymerase detaches
Translation
mRNA transcript attaches to ribosome
tRNA molecules collect amino acids from cytoplasm, ATP is required to form the bond
Anticodon of tRNA base pairs with first codon of mRNA
amino acid on first tRNA forms peptide bond with amino acid on 2nd tRNA
First tRNA detaches and picks up another amino acid
mRNA moves along
Stop sequence is reached, polypeptide May be transferred to RER for folding
Splicing
In eukaryotic nuclei
Pre-mRNA made to mRNA
Non coding section cut out to leave only exons
Prokaryotic dna don’t have Introns so don’t need splicing
Gene mutations
A random change in the base sequence of a gene
Occur when the DNA molecule is replicated
Three types of gene mutation
Substitution
Deletion
Addition
Neutral/ silent mutation
Change in bases has affect to the function of the protein
As the dna code is degenerate
Mutagenic agents
4
High energy radiation
Ionising radiation
Chemicals
Viruses
Know as carcinogens
Chromosome mutations
3
Occur spontaneously and at random during meiosis
Homologous chromosomes sometimes don’t separate and a gamete will have two chromosomes of the same type
When the gamete fuses with another the zygote will have three chromosomes instead of just a pair
Meiosis
5
The division of a diploid cell to four haploid daughter cells
Not genetically identical - due to crossing Over and independent segregation
When two haploid fuse, diploid chromosome number is restored
In meiosis I homologous chromosomes are separated
In meiosis II sister chromatids are separated
Crossing over
4
Occurs in meiosis I
Homologous chromosomes come together to form a bivalent
Non sister chromatids wrap around each other and form a chiasmata
Chromosomes break and rejoin swapping sections which leads to new combination of alleles
Independent segregation
In the first meiotic division the homologous pairs of chromosome randomly align at the equator and then separate at opposite poles
Genetic diversity definition
The number of different alleles of genes in a population
Allele definition
A different form of gene
Adaptation definition
A characteristic that increases an organisms chance of survival/ reproductive success
Adaptation types (3)
Anatomical
Physiological
Behavioural
An organism with increased reproductive success is more likely to
Survive until it reproduces
Grow sufficiently well to reproduce successfully
Attract a mate
Natural selection
4
A gene mutates by random chance
Often they are harmful but occasionally the new allele might confer an advantage and lead to increased reproductive success
Organisms carrying the advantageous allele are more likely to reproduce and pass on the allele
Over many generations the new alleles increase in frequency
Genetic bottlenecks
3
Events that cause a big reduction in population
This reduces the number of different alleles and as a result there is low genetic diversity
The population then increased again but the genetic diversity stays low
Founder effect
3
When a small founder population becomes isolated form the original population
The small founder population will have a smaller gene pool and genetic diversity than the original population
It will increase in size but still have lower genetic diversity
Stabilising selection
Where individuals with alleles for phenotypic characteristics towards the middle of the range are more likely to survive, reproduce and pass on their alleles
Directional selection
2
Individuals with alleles which give characteristics of an extreme type are more likely to survive
More common when an environment changes
Species definition
A group of similar organisms able to reproduce to give fertile offspring
Courtship behaviour
3
Before animals can mate they have to recognise each other as being from the same species
There are behaviours performed which results in mating
Each species has a specific courtship behaviour
Advantages of courtship behaviour
3
Animals recognise and mate with adults of the opposite sex
Adults mate with adults of the same species
Healthy adults in good breeding condition
Examples of courtship behaviour
5
Birds perform dances Build decorated nests Display coloured feathers Song songs Female insects secrete pheromones
Can be used to classify organisms
Taxonomy
The study of the classification of organisms into a series of categories called taxa(taxon)
Hierarchical
Each organism is classified into a series of smaller and smaller taxa with no overlap between the taxa
Classification order
Domain Kingdom Phylum Class Order Family Genus Species
Binomial name
First part of the name is the genus
Second part is the species
The classification system is phylogenetic
Phylogeny is the study of the evolutionary history of organisms, all species have evolved from a shared common ancestor
Ways to classify species
5
Physical appearance
Immunological comparisons
Comparing DNA sequences/ genome sequencing
Comparing mRNA sequences
Comparison of amino acid sequences in proteins
Classifying
Physical appearance
Looking at the general physical features
Physical appearance is largely determined by genes
Classifying
Immunological comparisons
5
Antibodies bind to proteins of a specific shape only.
When antibodies from one animal are added to proteins from another, they will bind if they are similar shape
The more closely related they are, the more similar the shape and more likely to bind
When they bind they usually precipitate
The more precipitate, the more similar
Classification
Comparing DNA sequence
2
Computer programs can now make very rapid comparisons between the sequence of two species
The more similar, the more recently the species shared a common ancestor
Classification
Comparing mRNA sequences
Large data bases can be accessed in order to make comparisons
mRNA is easier to extract than DNA as it is in the cytoplasm
Classification
Comparison on amino acids
Sequence of amino acids is determined by DNA gene sequence
Closely related species have very similar DNA sequence, therefore amino acid sequences
Biodiversity definition
3
The variety of living organisms in an area including the microbes, plants and animals
High biodiversity Is desirable
Global biodiversity is higher at the equator and lower at the poles
Community definition
A group of interacting population of different species living in the Same place at the same time
Population definition
A group of organisms belonging to the same species found in the same area at the at the same time and potentially able to interbreed
Habitat definition
The environment in which an organism or population of organisms usually lives
Species richness definition
A measure of the number of different species in a community
Estimate by random sampling
Index of biodiversity takes into account
Both species richness and the number of individuals
Index of biodiversity equation
D= TOTAL(TOTAL-1)/ sum n(n-1)
A higher biodiversity index means
A more biodiverse environment
Index of biodiversity is useful as
It allows the diversity of different areas to be compared or the diversity of one area to be monitored
Conservation definition
Actively managing ecosystems in order to increase biodiversity
Mono culture definition
Large fields growing one crop only
UK farming/ agriculture
Provide plentiful and cheap food, wood, wool and leather
Farmers use many methods to manage land effectively and produce maximum yield
Intensive farming increase the yield and it has doubled in the last fifty years
However it lowers biodiversity
Intensive farming techniques
6
Clearing woodland- increase land availability for cultivation or grazing. Decrease trees and habitats.
Removing hedgerows- enlarge fields and area available for agriculture, increased intraspecific compétions between crops for light. Removes habitats which could be pests, also removes corridors.
Spraying pesticides- kills invertebrates which eat crops,also kills polenating insects, reduced food of insects for food chain
Spraying herbicides- kills weeds. Removes food which is bottom of food chain
Growing monocultures- growing one crop reduces variety of habitats and biodiversity
Improving grazing land- sowing, provides cows and sheep with nutritious fodder, outcompetes other plants so loss of habitat
Conservation measures
Environmental stewardship scheme- encourages farmers to replant hedgerows
EU has banned use of various insecticides
Endangered species protected
Natural parks
Genetic diversity definition
The number of different alleles of genes in a population
Variation definition
The differences that exist between individuals within a species and between different species
Standard deviation
Running means etc
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