Genetic info, variation & relationships between organisms

• DNA in prokaryotes v DNA in eukaryotes

  prokaryotes: smaller, circular & has no associated proteins

  • can't form chromosomes
  • eukaryotic mitochondria & chloroplasts has prokaryotic-like DNA in them

  eukaryotes: longer, linear & has associated proteins (histones)

  • can form chromosomes
  • chromosomes = thread-like structures consisting of 1 DNA strand wrapped around a histone
  • chromosomes found in nucleus & only visible during cell division
• DNA = stores genetic information which codes for proteins & passes on genetic information for generations

  • is a double helix - helix wound around histones
  • DNA-histone complex is wound up further to become chromosomes
  • humans have 46 chromosomes (23 homologous pairs)
  • fertilisation = fusion of sperm & egg cell
  • homologous pair = chromosomes with the same genes in the same order but with variation in the genes between them
  • pair formed from 1 maternal & 1 paternal chromosome
• Allele = different versions of the same gene

  • each gene has at least 2 alleles of itself - 1 taken from each parent
  • may be the same allele inherited or different
  • different allele -> different sequence -> different protein/polypeptide formed -> may change ability for protein to function
  • mutations = changes to the base sequence of a gene
• 
  

  Genome = complete set of genetic information in an organism

  proteome = complete set of proteins expressed by a cell

  • every cell contains genome for the full range of proteins
  • in reality -> each type of cell under certain conditions only produce some proteins from the genome

  T1 FOR DNA & RNA NOTES
• gene = section of DNA that codes for polypeptides & functional RNA

  • functional RNA = non-coding RNA
  • locus = position of gene on DNA

  base triplet = 3 bases coding for an amino acid

  • only 20 different amino acids
  • 3 bases give 64 (4^3) combinations which is enough
• Features of genetic code:

  • most amino acids have more than 1 triplet combination
  • degenerate code = > 1 triplet combinations to code for 1 amino acid
  • methionine amino acid = start code marking start of polypeptide
  • 3 different triplet codes code the 'stop' amino acid marking end of polypeptide
  • triplet always read in 1 direction
  • triplet is non-overlapping -> each base only read once
  • triplet is universal -> same triplet for amino acid in all organisms
• exons = sequences of bases in genes that code for an amino acid/proteins


  introns = non-coding base sequences in a gene

  • can control if a gene is expressed
• Protein synthesis:Transcription = making of mRNA using DNA as a template strand

  1. DNA helicase unwinds & unzips DNA by breaking H bonds inbetween
  2. RNA polymerase binds to promoter region on gene
  3. promoter region = DNA sequence signals where RNA polymerase binds & transcripts from
  4. One DNA strand acts as template strand & free floating RNA nucleotides form complementary base pairs with DNA strand
  5. RNA polymerase forms phosphodiester bonds between RNA nucleotides
  6. RNA polymerase stops at terminator sequence
  7. terminator sequence = bases sequence signalling when RNA polymerase detaches

  pre-mRNA formed
• Splicing = removal of introns from pre-mRNA to form mRNA

  • introns prevent polypeptide from forming
  • happens in nucleus & mRNA leaves via nuclear pores after
  • splicing only happens in eukaryotes
  • prokaryotes don't have introns so mRNA is immediately formed
• Protein synthesis: Translation = forming of polypeptide chain using mRNA base sequence and tRNA

  1. mRNA leaves nucleus & attaches to a ribosome from the start codon
  2. tRNA with complementary anticodon attaches to start codon
  3. tRNA has specific amino acid attached to it & held is place by ribosome
  4. Ribosome moves along mRNA to attach to 2 amino acids on tRNA by peptide bond
  5. catalysed by enzyme & ATP
  6. Continues until ribosome reaches stop codon on mRNA & ribosome detaches

  • polypeptide enters golgi body for folding & modification
• Meiosis = cell division forming 4 genetically different daughter cells with half the amount of DNA as the parent cell

  • haploid cells produced
  • to maintain constant no. of chromosomes in adult of species
  • occurs in sex organs
• Genetic diversity: Crossing Over

  • prophase 1 - homologous pair of chromosomes formed
  • chromatids from each pair cross over & twist around each other
  • twisting causes portion of chromatids to break off
  • broken portions rejoin with chromatids of its homologous pair
• Genetic diversity: independent segregation

  • when homologous pair of chromosomes line up in metaphase - random line up of homologous pairs
  • 2^n = total no. of possible chromosome combinations
  • n = number of chromosomes
• Meiosis I

  Prophase I:

  • chromatic condense and coils
  • homologous pairs form
  • bivalents = homologous pairs of chromosomes

  Metaphase I:

  • bivalents line up along equator

  Anaphase I:

  • homologous pairs pulled by spindle fibres to poles of cell
  • independent segregation occuring

  Telophase I:

  • chromosomes reach poles & often go straight into meiosis II
  • spindle breaks down & nuclear envelope reforms
• Meiosis II

  Prophase II:

  • spindle forms at right angle to original spindle
  • nuclear envelope breaks down if reformed

  Metaphase II:

  • chromosomes line up at equator of the cells with spindle attached to centromere

  Anaphase II:

  • spindle fibres shorten causing centromere to divide & chromatids to seperate

  Telophase II:

  • chromosomes reach poles & uncondense
  • nuclear envelope reforms & spindle breaks down

  4 haploid cells formed
• Mutation = random change in the sequence of bases in a gene

  • gene mutation = changes to 1 or more nucleotides or a change in the DNA base sequence
  • silent mutation = gene mutation that doesn't affect the amino acid coded for
  • due to DNA being degenerate
  • mis-sense mutation = gene mutation that changes the amino acid coded for
• • substitution mutation = type of gene mutation where a nucleotide replaced with another nucleotide with a different base
  • may code for a different amino acid & affect bonds formed tertiary structure of protein -> can't function
  • nonsense mutation = type of substitution mutation where a premature 'stop' codon coded for
  • deletion = type of gene mutation where a nucleotide is lost from DNA sequence
  • has a 'knock-on' effect called a frameshift & changes way DNA is read
  • insertion = type of gene mutation where a nucleotide is added to DNA sequence
  • also causes a frameshift
• chromosomal mutations = changes to the structure or number of whole chromosomes

  • polyploidyl = condition caused by a change in whole sets of chromosomes
  • occurs when organisms have 3 or more sets of chromosomes instead of 2 but mainly occurs in plants (humans wouldn't develop)
  • non-disjunction = condition caused by changes in the number of individual chromosomes
  • when individual homologous pairs of chromosomes fail to seperate in meiosis
  • leads to having 1 more or 1 less chromosome
  • thus all cells of adult of species have 1 more or less chromosome
• Required practical 6: effect of antimicrobial substances on microbial growth

  method:

  1. spray bench with disinfectant & wipe down with paper towels
  2. place bunsen burner on heatproof mat & light it
  3. name & date the underside of the agar plate
  4. wash your hands
• genetic diversity = total number of different alleles in a population

  • population = a group of individuals of the same species that live in the same place and can interbreed
  • greater no. of different alleles in a species -> greater genetic diversity of that species
  • types of genetic adaptation:
  • structural adaptation - e.g. fur colour
  • physiological adaptation - e.g. levels of fat stored
  • behavioural adaptation - e.g. using rocks to get food
• reduction in genetic diversity

  genetic bottleneck = population is greatly reduced in size by an extreme event, limiting the genetic diversity of the species

  • smaller gene pool -> less genetic variation

  founder effect = small number of organisms form a new population and only have a few different alleles from the initial gene pool

  • completely changes frequency of alleles in new colony compared to larger parent colony
  • may lead to more genetic disease
• natural selection = process in nature causing individuals with advantageous traits to be more likely to survive & reproduce & pass on those traits to their offspring

  • genetic diversity is the enabling factor of natural selection
  • only certain individuals are reproductively successful -> affects allele frequency in a population

  A) random mutation occurs & causes genetic diversity

  B) new allele may now by advantageous to the possessor

  C) individuals more likely to survive thus reproduce

  D) greater proportion of next gen. inherits adv. allele

  E) over gens. allele frequency increases in population

  
• selection pressure = an evolutionary force causing particular phenotype to be more favourable in a certain environmental conditions

  • polygenes = multiple genes that influence a characteristic
  • more likely to be influenced by the environment

  directional selection = the environment favours individuals with alleles for charactersitics of an extreme type

  • mean changes

  stabilising change = the environment favours individuals with alleles for characteristics closer to a specific value

  • mean stays the same but the standard deviation decreases over time

  A) directional selection

  B) stabilising selection

  
• classification = grouping of organisms

  • artificial classification = groups organisms based on differences useful at the time
  • called analogous characteristics = characteristics with same function but different origins
  • phylogenetic classification = hierarchy where groups contained within larger composite groups & have no overlap
  • no overlap -> every item fits in 1 species
  • based on phylogenetic trees between organisms & ancestors' shared characteristics
  • homologous characteristics = characteristics with similar evolutionary origins regardless of function in adult of species
• phylogeny = evolutionary relationships between organisms

  • phylogeny of an organism reflects the evolutionary branch that led to it (modeled by phylogenetic trees)

  taxonomy = theory & practice of biological classification

  • taxon = groups within a phylogenetic biological classification
  • taxonomic rank = position of a group in the heirarchy
• 3 domains by Carl Woese

  Archaea = single-celled prokaryotes with some eukaryotic features

  • protein synthesis more like eukaryotes
  • no murein in cell walls -> fatty acids bonded via ether linkages
  • 1 kingdom: archaebacteria

  bacteria = single-celled prokaryotes

  • has 7OS ribosomes (smaller than eukaryotic ones)
  • 1 kingdom: eubacteria

  eukarya = organisms made of 1 or more eukaryotic cells

  • 4 kingdoms: protista (single-celled) , fungi, animalia, plantae
• Domains further divided + binomial naming system

  Domain - Kingdom - Phylum - Class - Order - Family - Genus - Species

  • species = group of organisms with similar characteristics and are able to breed & produce fertile offspring

  Generic name specific name (may be underlined or in italics)
• Members of same species have same/similar genes - resemble each other, physically, biochemically & in terms of BEHAVIOUR

  • behaviour is genetically determined -> helps organisms distinguish their own & can evolve to increase survival chances
  • adaptations increasing courtship:
  • recognising members of own species
  • identify mate capable of breeding
  • form a pair bond
  • synchronise mating
  • become able to breed
  • courtship behaviour helps determine if female is at receptive stage & is usually a chain of actions
  • different per species
• Agricultural ecosystems

  Biodiversity = variety of living organisms in an area

  • indicates how well an ecosystem is likely to function
  • high diversity -> more likely to survive

  Importance of increasing agricultural yield?

  • increased food production for increasing population
  • affordable food
  • food security

  how yield has been increased?

  • improved genetic varieties of plants & animals
  • use of fertilisers & pesticides (fungicides, herbicides, insecticides)
  • use of machinery
  • removal of hedgerows, ponds & woodland
  • use of monocultures
• agricultural ecosystems

  consequences of intensive farming?

  • reduced plant species
  • reduced variety of food sources and habitats
  • reduced biodiversity

  Conservation methods?

  • re-introduce hedgerows
  • stop draining ponds
  • plant native trees
  • biological control - leave field verges & edges for wildflowers
  • intercropping - crop rotation with nitrogen fixing crops e.g clover
  • reduce use of pesticides
• diversity within a community

  • species diversity = no. of different species & individuals of each species in any community
  • ecosystem diversity = range of different habitats
  • species richness = no. of different species in a particular area at any given time
  • same no. of species but differing proportion
  • Simpson's diversity index = measure of diversity considering both no. of species & relative abundance of each species
  • species richness & evenness increases -> greater diversity
  • n = total no. organisms of each species & N = total no. organisms of all species

  A) N(N-1)

  B) sum of n(n-1)