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Section 4 - Genetic information, variation, and relationships between…

- - - - Genetic code
        
        Non-overlapping
        
        Universal
        
        Each triplet codes for the same amino acid in every organism
        
        Degenerate
        
        Multiple triplets code for one amino acid
        
        Sequence of three bases e.g. GGA codes for a specific amino acid e.g. glycine
      - Found at a specific position on a DNA molecule
        
        Locus
      - Base sequence of DNA
        
        Codes for the amino acid sequence of a polypeptide, or a functional RNA
        
        Ribosomal RNA and transfer RNA
    - - Most of the DNA does not code for proteins
        
        Large regions of repeats of bases between genes
        
        Exon = coding sequence within a gene
        
        Intron = non-coding sequence with a gene
      - DNA is long and linear
        
        DNA and histones are tightly coiled to form chromosomes
        
        Associated with proteins (histones)
    - - DNA is short and circular
        
        Not associated with proteins
      - Same type of DNA in prokaryotes as mitochondria and chloroplasts
  - - - Complete set of genes in a cell
      - Proteome
        
        Complete set of proteins the cell can produce
    - - Transfer RNA (tRNA)
        
        Small molecule, 80 nucleotides
        
        Single stranded molecule
        
        Clover leaf shape
        
        Specific amino acid attached to tRNA
        
        Anticodon at one end, bases complementary to mRNA codon
      - Messenger RNA (mRNA)
        
        Long, single stranded molecule
        
        Sequence of bases is complementary to sequence of DNA
        
        Produced in nucleus, leaves via nuclear pores to go to ribosomes
        
        Codon = sequence of 3 bases that codes for an amino acid, complementary to a triplet
        
        Codons on mRNA determine amino acid sequence
      - Has a ribose sugar and uracil instead of thymine
    - - Translation
        
        Synthesising the protein at the ribosome
        
        Ribosome attaches to the starting mRNA codon
        
        tRNA with complementary anticodon pairs with mRNA codon
        
        Ribosome moves along mRNA, two tRNA molecules are held at once
        
        Peptide bond forms between adjacent amino acids
        
        Polypeptide chain forms
        
        ATP and enzyme required
      - Transcription
        
        Pre-mRNA is spliced
        
        Removal of introns
        
        Pre-mRNA is only present in eukaryotes
        
        RNA polymerase
        
        mRNA leaves via a nuclear pore
        
        Producing complementary mRNA from DNA
- - - - A change in the base sequence of DNA
      - Can arise spontaneously during DNA replication in interphase
        
        Can give rise to cancerous cells
      - Base deletion
        
        May cause a frameshift
        
        Completely different codons and amino acids, and so, a different protein is synthesised
      - Base substitution
        
        May cause a change in one amino acid
        
        Change to structure and folding of protein
        
        New codon may code for same amino acid as original codon, so no change in protein
        
        Degenerate nature of genetic code
    - - Changes in the number of chromosomes
      - Example - in Down's syndrome, there are three copies of chromosome 21 due to non-disjunction
      - Polyploidy - having more than one set of chromosomes
        
        Can occur in plants
      - Chromosome mutations often arise during meiosis due to chromosome non-disjunction
    - - Produces 4 daughter cells
      - Each cell has half the number of chromosomes of the parent cell (haploid)
      - Produces gametes (egg and sperm)
      - Meiosis I - 1st division
        
        Homologous chromosomes pair up and separate into 2 daughter cells
        
        Independent segregation of homologous chromosomes
        
        Crossin over of alleles
        
        New genetic combinations, increased genetic variation
      - Meiosis II - 2nd division
        
        Chromatids separate
        
        4 gametes with 23 chromosomes (for humans)
        
        All genetically different from each other
  - - - Gene pool
      - Genetic diversity = number of different alleles in a population
        
        Greater diversity = more likely individuals in a population will survive an environmental change
      - Genetic diversity contributes to natural selection
      - Enabling factor
    - - Random mutations results in new alleles
        
        Most of the time, these new mutations are harmful, but sometimes they can confer an advantage
        
        The advantage means the organism is better adapted, so survives and reproduces
        
        Adaptations may be behavioural, anatomical, or physiological
        
        Better reproductive success
      - Results in species that are better adapted to their environment
        
        Frequency of non-advantageous alleles decreases
        
        Over many generations, the frequency of the beneficial allele increases
        
        New allele is inherited by offspring
        
        Better reproductive success
    - - Directional
        
        Favours individual organisms that vary in one direction from the mean
        
        Antibiotic resistance in bacteria
        
        Changes characteristics of the population
      - Stabilising
        
        Human birth weights
        
        Preserves characteristics of a population
        
        Favours individual organisms with the mean characteristics
- - - - Taxonomy - classifying biological organism into groups
      - Phylogenetics - classifying organisms into groups based on evolutionary relationships
        
        Advances in gene technology have allowed us to identify and clarify evolutionary relationships
        
        Originally based on shared characteristics
        
        A hierarchy
        
        Domain, kingdom, phylum, class, order, family, genus, species
        
        Smaller groups within larger groups
        
        No overlap
        
        Each group is a taxon (plural taxa)
      - Binomial naming
        
        First name = generic name, the genus name
        
        Second name = specific name, the species name
        
        Example = homo sapiens
    - - Two organisms are of the same species if they can breed together to
      - Similar to terms of appearance, biochemical processes and behaviour
      - Courtship behaviour is essential for successful mating
        
        To ensure the other member is in a physiological state to breed
        
        To synchronise mating
        
        Forms a pair bond
        
        Important for survival of offspring
        
        Can identify a mate capable of breeding
        
        Need to be fertile, mature, and receptive
        
        Can recognise members of own species
        
        Different behaviours for different species
  - - - The higher the biodiversity, the more stable the ecosystem is
        
        Some individuals can survive environmental change
      - The variety of life in a habitat ranging from small ecosystems to the Earth itself
      - Ecosystem diversity = the range of habitats
      - Genetic diversity = variety of genes in a population of a species
      - Species diversity = range of different species and individual members of species in a community
        
        Species richness is a way of measuring species diversity
        
        Species richness is the number of different species in a community
    - - D = (N(N - 1)) / (Σn(n - 1))
        
        N = the total number of organisms of all species
        
        n = the total number of organisms of each species
      - Index of diversity takes into account the number of individuals of a species, so is a better measure of diversity
    - - Farming reduces biodiversity
        
        Use of pesticides
        
        Large space for one species only, other species compete for remaining resources
      - Techniques to improve biodiversity in agricultural ecosystems
        
        Creating ponds
        
        Using organic fertilisers
        
        Using nitrogen-fixing crops
        
        Planting trees and hedges
  - - - The amino acid sequence of a protein is determined by mRNA, which in turn is determined by DNA
      - Similar sequences of amino acids indicate more closely related species
    - - Inter- and intra- specific variation
      - Data collection
        
        Normal distribution curves
        
        Mean and standard deviation
        
        Large standard deviation = large variation
      - Sampling
        
        Random sampling reduces sampling bias
        
        Large sample size to reduce chance
        
        Statistical analysis to see if the results were the result of chance
    - - Observable features can be changed by the environment, so not reflective of DNA differences
      - Most observable features are polygenic - coded for by more than one gene
        
        Tend to vary continuously, so difficult to distinguish
      - As observable features are determined by DNA and proteins, it is useful way of seeing similarities and differences
    - - Gene technology allows us to read the base sequence of DNA and mRNA
      - Cam compare how similar the base sequences are between species
        
        More similar DNA = more closely related in evolutionry history
      - As mRNA sequences are complementary to DNA, we can also read the mRNA to ascertain how closely related species are