genetic variation + mutations

• genetic variation can occur through...

  • independant assortment
  • crossing over
• independant assortment

  • different combinations form of parental chromosomes
  • occurs in metaphase 1
• crossing over

  • occurs in prophase 1
  • sections of chromosomes are swapped
  • non sister chromatids entangle and form chiasma
  • DNA strand break and fragments join
  • form new combination of allele
• chromosome mutations

  • when sections of chromosomes change
  • 2 types: translocation and non disjunction
• translocation mutation

  
  

  • base sequence in chromosome swapped with non homologous chromosome
  • occurs in interphase
  • DNA molecule breaks and rejoined by DNA ligase in wrong place
• issues with translocation mutations

  • if mitosis occurs, gametes with have missing regions of chromosomes
  • gene disrupted
  • no longer functions
• non disjunction mutation


  • chromosomes don't separate properly in meiosis
  • occurs in anaphase
  • chromosome is stuck on one pole of cell
  • leads to polysomy and monosomy
• monosomy

  • gamete with missing chromosome is fertilised
  • only 1 copy instead of 2

  e.g Turner's syndrome - appear female but have no sex organs

  • fatal for embryo development as full set is needed.
• polysomy

  • gamete with extra chromosome is fertilised

  e.g trisomy-21 (down syndrome)

  • 3 copies of chromosome form