4. genetic diversity and evolution

• species- a group of similar organisms that can successfully breed together to produce fertile offspring
• mutagenic agents- increases rate of mutation by physical/ chemical factors such as; ionising radiation or carcinogenic chemicals
• substitution mutation

  • substitute replaces one base with another
  • number of bases stays the same
  • no frameshift
• deletion/ insertion mutation

  •  takes away/ adds bases so number will decrease/ increase
  • frameshift occurs and different protein produced
• how mutation leads to production of a non-functional enzyme

  • change in base sequence of DNA
  • causes change in amino acid sequence in 1°
  • which changes hydrogen, ionic and disulphide bonds in 3°
  • which will change the active site of an enzymes
  • substrate no longer complimentary so no ES complexes form
• how chromosomes produce genetic variation in gametes

  • crossing over of chromatids
  • independent segregation in second cell division
• meiosis

  • 2 cell divisions, produce 4 non-identical daughter cells
  • variation caused by random assortment and crossing over of chromatids
  • crossing over occurs in first cell division
  • produces half the number of chromosomes
• how meiosis produces haploid chromosomes and shows genetic variation

  • homologous chromosomes pair up
  • crossing over occurs producing new combination of alleles
  • chromosomes separate at random
  • producing a varying combination of chromosomes
  • chromatids separated at meiosis 2 (independent assortment)
• crossing over occurs at the chiasma
• how crossing over causes genetic variation (4)

  • homologous chromosomes from a bivalent
  • sister chromatids exchange alleles at chiasma
  • producing new combination of alleles
• genetic diversity- number of different alleles of genes in a population
• natural selection- process by which organisms better adapted to the environment survive and reproduce and pass on their advantageous alleles to their offsprings producing different phenotypes
• variation- differences in the base sequence of DNA or amino acid sequence of proteins
• variation

  • genetic: mutation, meiosis independent assortment or crossing over, fertilisation of gametes
  • environmental: climate change, availability of water/food, light intensity, water and nutrients in soil
• genetic bottleneck- reduce number of different alleles, reduce genetic diversity. survivors produce larger populations but reduced diversity remains
• founder effect- start a new colony due to geographical isolation
• natural selection

  • (geographical isolation occurs therefore no interbreeding/ reproductive isolation)
  • there is variation in a population
  • due to mutation some have favourable alleles which allow them to survive and reproduce
  • pass on favourable alleles to offsprings, so frequency of alleles in population increase
• stabilising selection (5)

  • occurs in unchanging environment
  • selection for the mean
  • range of standard deviation is reduced
  • increased proportion of population becomes well adapted to the environment
  • increasing allele frequency
• directional selection

  • individuals with alleles for a single extreme phenotype are more likely to survive and reproduce
  • change due to environment increasing allele frequency
• anatomical- internal or external physical feature

  -camouflage, mimicry

  -waxy cuticle, spines
• behavioural- acts are inherited or learned through experience

  -migration

  -phototropism- growing towards the light
• physiological- process inside an organism

  -kidney adaptations

  -toxin production
• uses of phosphates: make RNA,DNA, ATP, ADP, membranes, phosphorylation
• why clear zone around each paper disc

  antibiotics diffuse out of paper disc and inhibit growth and kill bacteria
• aseptic technique

  • flame any instruments to kill microorganisms
  • disinfect work surfaces to kill microorganisms
  • lift lid of petri dish only slightly so unwanted microbes don't contaminate culture
  • use bunsen burners to create a convection current
  • wash hands to kill microbes
• degenerate - several codons code for one amino acid