Unit 3a-Genetic Diversity

• What is a mutation?

  change in the quantity or sequence of DNA bases
• What are the 3 ways a mutation in the DNA base sequence can occur?

  Substitution

  Insertion

  Deletion
• What is the subsitition mutation?

  A mutation when a base in the DNA sequence is replaced for another base
• What are the 3 forms that substitution mutation can take?


  Silent

  Missense

  Nonsense
• What are silent mutations?

  Mutation that does not alter the amino acid sequence of the polypeptide
• What are missense mutations?

  Mutation that alters a single amino acid in the polypeptide chain
• What is a nonsense mutation?

  Mutation that creates a premature stop codon which causes the polypeptide chain produced to be incomplete which affects final protein structure and function
• What is a deletion mutation?

  mutation occurs when a nucleotide is randomly deleted from DNA sequence
• What is a frameshift mutation?

  If one nucleotide is deleted or inserted the triplet codes that follow are changed which shifts the reading frame of the DNA sequence
• What is an insertion mutation?

  Mutation when a nucleotide ( with a new base ) is randomly inserted into DNA sequence
• What are chromosome mutations?

  Changes in the structure or number of whole chromosomes
• What are the 2 forms of chromosome mutations?

  Changes in whole sets of chromosomes

  Changes in number of individual chromosomes
• What is a polyploid?

  An organism with 2 or more sets of chromosomes
• What are changes in the number of individual chromosomes caused by?

  homologous pairs fail to separate during meiosis
• What is non-disjunction?

  homologous pairs fail to separate during meiosis
• What does non-disjunction result in?

  gametes with abnormal number of chromosomes
• Define the term mutagenic agent?

  factor that increases rate of mutations
• What is a bivalent in meoisis?

  Association of 2 replicated homologous chromosomes having exchanged DNA strands in at least one site called chiasmata
• What is a chiasmata?

  point of contact and exchange between homologous chromosomes during meiosis.
• What is mitosis?

  Cell division that produces 2 genetically identical diploid daughter cells
• What is meiosis?

  Cell division that produces 4 genetically dissimilar haploid daughter cells
• What organism produces spores by meiosis and gametes by mitosis?

  ferns
• What are the 2 ways in which meiosis creates genetic variation?

  crossing over of homologous pairs

  independent assortment
• What happens in interphase before meiosis?

  Chromosomes double

  Organelles double

  DNA checked
• What happens in prophase 1 in meiosis?

  Chromosomes condense

  Homologous pairs of chromosomes form a chiasmata as crossing over occurs

  Nuclear membrane breaks down

  Centrosomes move to poles of cell and spindle fibres start to form
• What happens in Metaphase 1 in meiosis?

  Pairs of homologous chromosomes line up along the spindle equator

  This lining up occurs randomly ( independent assortment)
• What is recombination in meiosis?

  Genetic material exchanged between homologous chromosomes
• What happens in Anaphase 1 in meiosis?

  Spindle fibres shorten

  Homologous pairs pulled to opposite poles of the cell
• What happens in Telophase 1 in meiosis?

  Nuclear membrane reforms

  Chromosomes recoil back to chromatin
• What is genetic variation?

  differences in DNA base sequences between individuals of a species
• What is genetic diversity?

  number of different alleles in a population
• What is gene pool?

  different alleles in a population
• Describe the stages of natural selection?

  Variation between population of individuals

  Random DNA mutation results in new allele

  New allele is beneficial to individual

  Individuals more likely to survive in environment ( selective advantage)

  Individuals live longer and reproduce passing the beneficial allele to offspring

  Over generations the frequency of beneficial allele increases
• What is gene flow?

  transfer of genes between populations
• What are the 3 types of natural selection?

  Stabilising

  Directional

  Disruptive
• Describe stabilising selection?

  individuals closest to the mean are favoured
• Describe directional selection?

  shift in one direction as there is a gradual change in allele frequency over several generations
• Describe disruptive selection?

  Extreme values for a trait are favoured
• What is an adaptation?

  feature that allows an organism to survive
• What are the 3 types of adaptations?

  Anatomical

  Physiological

  Behavioural