Biology Unit 4

  1. Homologous Pairs
    Chromosomes that are derived from each parent
  2. Autosomes
    All chromosomes except those that determine gender (44 in humans, 22 pairs)
  3. Sex Chromosomes
    Determine gender. There are usually two: XX = Female and XY = Male
  4. Apoptosis
    Programmed cell death for the benefit of the whole organism
  5. Name a situation in which a healthy cell dies because of apoptosis
    When the cell has outlived its usefulness for example plasma cells after an infection has passed
  6. Why is apoptosis of benefit to an organism?
    Saves energy and resources and does not cause inflammation, provides growth and development - replaces damaged cells
  7. Outline the series of events that occur during apoptosis
    • 1. Death signal recieved
    • 2. Caspases activated in early stages
    • 3. Cytoplasm begins to shrink, cell develops blebs. Apoptotic bodies form
    • 4. Apoptotic bodies engulfed and broken down by phagocytes
  8. Binary Fission
    Cell division for reproduction and for growth in bacteria.

    •  - Type of asexual reproduction
    •  - Not mitosis because: no nucleus involved, no centromeres, chromosomes attached to cell membrane
    •  - Similarities to mitosis: DNA replication, 2 cells are produced from 1 parent cell
  9. Why do cells divide?
    •  - For growth and development
    •  - To replace dead and damaged cells
  10. Mitosis
    Cell division for growth and repair
  11. Cytokinesis
    Division of cytoplasm that follows mitosis
  12. Advantages and disadvantages of asexual reproduction
    Advantage - if environment stays constant, then the species will remain well suited -  therefore survive and there is no need for a mate

    Disadvantages - if environment changes then the whole species is at risk of extinction because all individuals are genetically the same
  13. 4 examples of when organisms carry out apoptosis
    • 1. Formation of fingers and toes (removal of webbing)
    • 2. Cell has outlived its usefulness (plasma cells after an infection has passed)
    • 3. The cell was damaged and requires too much energy to be repaired
    • 4. Too old/ not efficient
    • 5. Does not pass the check points in mitosis
  14. Necrosis
    Necrosis occurs if a cell is seriously damaged by mechanical or chemical trauma and it causes damage to the cell membrane. The membrane can no longer control what enters and leaves the cell. Cells may die by bursting and leaking their contents into the cell environment
  15. Sexual Reproduction
    This type of reproduction requires cell division called meiosis and it only occurs in diploid germline cells found in gonads (ovaries and testes)
  16. Gene
    A segment og DNA that codes for a protein
  17. Allele
    Alternate forms of a gene e.g. fur colour (gene) could be black or white (alleles)
  18. Phenotype
    The biochemical, physiological and physical expression of the genotype which can be affected by the environment
  19. Genotypes
    Refers to the alleles of the genes that make up an individual e.g. Alibinism (phenotype) aa (genotype)
  20. Heterozygous
    The individual has two different alleles
  21. Purebreeding/homozygous
    Individuals has two identical alleles e.g. AA or aa
  22. Dominant
    If a trait is dominant, it is expressed in the heterozygote. Only one copy of the allele is required. E.g. Aa or AA
  23. Recessive
    Only expressed in the homozygous form, two copies of the allele are require to express the recessive trait e.g. only aa will express the trait
  24. Autosomal
    A gene that is carried on the autosomes, not the sex chromosomes
  25. Sex linked
    A gene that is carried on the sex chromosomes
  26. DNA
    The genetic code. Contains all genes. Codes for specific proteins found in the nucleus of eukaryotes. It is inherited instructions for an organism
  27. Non-Disjunction
    Is when a pair of chromosomes fails to disjoin or segregate so that 2 copies of chromosome are present in the gamete
  28. Non-disjunction in meiosis I
    Two gametes with an extra copy of chromosome 21 and two gametes missing chromosomes 21
  29. Non-disjunction in meiosis II
    One gamete with an extra copy of chromosome 21, one gamete missing a copy of chromosome 21 and two normal gametes, each with one copy of chromosome 21
  30. Aneuploidy
    Trisomy: Union of a gamete with 2 copies of one chromosome, with a normal gamete leads to 3 copies of the chromosome

    Monosomy: Union of a gamete without one chromosome with a normal gamete leads to only 1 copy of the chromosome
  31. Deletion
    Chromosome breaks in 2 places and a section is removed, the chromosome then rejoins
  32. Duplication
    A section of the chromosome has replicated so that a set of its genes repeat
  33. Inversion
    • The chromosome breaks in 2 places and the middle piece rotates 180o
  34. Insertion
    Part of one chromosome breaks off and inserts into another
  35. Translocation
    Part of one chromosome breaks off one chromosome and attaches to another
  36. Dihybrid - linked genes
    Genes are located close together on a chromosome and tend to be inherited together (however allele combinations can be altered by crossing over if the parent is heterozygous)
  37. Dihybrid crosses
    The genes are located on separate chromosomes and therefore the genes assort independently from one another
  38. The Genetic Code
    Refers to how bases are read (transcribed) into RNA and then translated into proteins
  39. The genetic code is:
    •  - Universal = some genetic code is used to translate proteins in all living things
    •  - Read in triplets 
    •  - Is non-overlapping (the codons do not overlap)
    •  - Degenerate or redundant (more that one codon can code for the same amino acid or stop)
  40. Genomics
    The study of whole sets of genes possessed by an organism
  41. Purposes/benefits of various genome projects
    •  - Learn more about important agricultural plants
    •  - To study animals that have diseases that can cross into humans
    •  - To improve diagnosis of human inherited disorders
    •  - To help identify people of risk of disease
    •  - For comparative genomics to study evolutionary relationships
  42. Limitations/problems associated with outcome of genome projects
    •  - Cost - money could be spent elsewhere - little benefit for whole community
    •  - Poluting of human genes
    •  - Exploitation of isolated populations and disadvantaged people in search of certain genes
  43. Genome
    All the information found in one set of an organisms chromosomes
  44. What does PCR stand for?
    Polymerase Chain Reaction
  45. Polymerase Chain Reaction
    Making many copies of segments of DNA from many very small shapes
  46. Why is Taq polymerase necessary?
    Because there is a need to use an enzyme to build/join nucleotides that does not denature in high temperatures. Taq Polymerase is derived from bacteriathat lives in hot springs
  47. Gel Electrophoresis
    To separate DNA using an eletric current as DNA is negatively charged. Smaller mass or size of DNA travel further than DNA with larger mass
  48. What is the role of DNA markers
    A group of DNA fragments of known lengths that can be used to work out unknown lengths of DNA run on the same gel
  49. What is the role of the loading dye
    To add colour to the sampleto make loading of the gel easier and to know how long to apply the electric current
  50. What is the role of ethidium bromide
    Binds to DNA to make it visible under UV light
  51. Genetically modified organism
    The genes of an organism has been altered/changed
  52. Transgenic organism
    Gene from a different source has been added from another organism
  53. Role of restriction enzymes
    To recognise a specific base sequence and cut the DNA at his point
  54. Blunt ends
    When restriction enzymes cut the DNA molecule at bases directly opposite each other
  55. Sticky ends
    When restriction enzymes cut the DNA unevenly - when the cutting sites are not directly opposite each other
  56. Stages of Gel Electrophoresis
    • 1. Fragments are placed in wells on the gel
    • 2. The gel is then placed in a bath and covered with a pH controlled solution
    • 3. A power source is attached to the bath and it is switched on. As DNA is negatively charged it moves through the gel towards the positive terminal
    • 4. The fragments are separated according to their size/mass
    • 5. To view the separated DNA fragments, ethidium bromide is added that attaches to the DNA. This dye is visible under ultraviolet light
    • 6. Samples of known length and weight (called: strandards) can be run on the gel for comparison
  57. PCR mixtures require:
    • 1. A segment of DNA, which acts as a template to make millions of copies
    • 2. A source of the four DNA nucleotides
    • 3. A DNA polymerase which is a heat resistant enzyme found in prokaryote Thermus Aquaticus
    • 4.  Single stranded DNA primers, which are synthetic, short pieces of single stranded DNA that are complementary to sequences of bases that flank the DNA region to be amplified. Specify the starting and finsihing points for DNA replication
  58. Purposes of DNA sequencing and sequencers
    •  - To work out the specific base sequence for a gene
    •  - To produce a probe
    •  - To identify base differences in a gene suspected to be the cause of a genetic disorder
    •  - To make a DNA sequence from a known amino acid sequence or mRNA strand
  59. What is genetic engineering?
    The modification or alteration in DNA of an organism and can involve the insertion of a gene froma  different species

    • Specific examples include:
    •  - human insulin gene into bacteria
    •  - insect resistance gene into bacteria and then into a plant
  60. A vector
    A carrier that allows the gene to be transferred from one organism into another 
  61. A plasmid
    A small circular ring of DNA which can self replicate
  62. Transformation (plasmids)
    When a recombinant plasmid is inserted into prokaryotes i.e. bacteria
  63. Transfection
    When foreign DNA is placed into eukaryotic cells
  64. Gene therapy
    Involves the insertion of a normal, functioning allele into human cells (viruses are the vectors of choice for inserting genes into animals/humans)
  65. Neo-Darwinism
    This refers to evolutionary theory that includes the concept of natural selection AND incorporates genetic drift, gene flow and polyploidy
  66. Relative Age
    • Deduced based on stratigraphy
    •  - Lowest rock is the oldest

    Not always accurateif layers have been altered by folding, buckling, reburyign or eroding
  67. Approximate Age
    Can be deduced if there are indicator or index fossils
  68. Absolute Age
    Can be worked out etiher by using radiometric methods or by non-isotopic methods
  69. Radiometric Methods (absolute age)
    Radioactive isotopes decay into different forms at a constant rate for a particular element. It is possible to calculate the amount of decay based on the isotopes half life to work out the age of the fossil or rock
  70. Half life
    The time taken for half the atoms in a radioactive sample to decay
  71. Carbon dating
    Can be used to date fossils of living organisms (wood, shells, peat, bone, animal tissue - that is, they are made up of carbon) up to 50, 000 years old because after this time there is too little radioactive carbon remaining.
  72. Non-isotopic methods
    •  - Electron-spin resonance
    •  - Thermoluminescence
    •  - Tree rings
  73. Divergent Evolution
    Where closely related species (sharing a recent common ancestor) become less similar over time due to different selection pressures.

     - Formation of homologous structures e.g. the forearm in bats, humans, and whales
  74. Adaptive Radiation
    Rapid divergent evolution - a very recent common ancestor evolves/diverges into a cluster of related species e.g. the finches
  75. Convergent Evolution
    The development of similar features in unrelated organisms due to similar selection pressures.

     - Formation of analogous structures e.g. streamlining of dolphins and sharks
  76. Species
    Organisms that can interbreed to produce viable and fertile offspring
  77. Speciation typically involves:
    • 1. Population is separated into smaller groups so that the small group becomes geographically isolated and there is no gene flow.
    • 2. Over many generations, the isolated population is subjected to different selection pressures because of different environmental conditions (= natural selection) and/or to other change factors such as genetic drift
    • 3. The isolated population changes over time such that, even if the two populations were to come together again, their members are unable to produce viable and fertile offspring.

    They are now two distinct gene pools and two different species i.e. they are reproductively isolated
  78. Discontinuous variation
    Discrete, non-overlapping classes of phenotypes - usually due to monogenic inheritance
  79. Continuous variation
    Many intermediate forms of the phenotype which show a normal distribution - usually due to polygenic inheritance
  80. Artificial Selection
    Where humans control the breeding of organisms so that individuals with desriable traits are mated to increase the likelihood that offspring will also display these traits
  81. Gene flow
    Movement of alleles due to reproduction between 2 different populations (same species) i.e. migration and breeding with other populations
  82. Random genetic drift
    A change in allele frequencies due to chance, rather than natural selection. Some causes - fire, earthquake
  83. Population bottlenecks
    Occurs when there is a severe reduction in the size of a population so very few individuals remain - very little genetic diversity in surviving population - more susceptable to extinction especially if there is environmental changes
  84. Founder Effect
    When a small number of pioneers (founders) begin a new population and so there is little genetic diversity
  85. Gene pool
    All of the alleles in a population
  86. Helicase
    Enzyme which breaks hydrogen bonds between 2 DNA strands so replication can occur
  87. DNA polymerase
    Enzyme that allows complementary DNA nucleotides to bind (via H bonds)
  88. DNA Ligase
    To seal the deoxyribose-phosphate  backbone (between the okasaki fragments to the lagging strand in DNA replication)
Card Set
Biology Unit 4
Biology Terms Unit 4