genetic variation

• what are two ways genetic variation is introduced?

  crossing over and independent segregation
• • crossing over is when two chromosomes wrap around eachother and exchange genetic material
  • a bivalent is an attached pair of chromosomes
  • a chiasma is points where chromatids join
  • the new chromosomes are called recombinant chromosomes
• independant segregation

  • when homologous pairs line up randomly at the equator and seperate
• how do you find the number of genetically different gametes produced by independant segregation ?

  2 to the power of n

  n is the number of homologous chromosome pairs
• meiosis involves two nuclear divisions and creates 4 genetically different haploid cells from a single diploid parent cell
• in meiosis 1 the homologous pairs are seperated

  in meiosis 2 the sister chromatids split
• variation occurs in meiosis 1
• crossing over

  • homologous pairs line up randomly at the equator
  • chromatids can become twisted and put tension causing them to break
  • broken parts recombine with the other chromatid
• further variation introduced when a random sperm and egg fuses so its (2^2)^2