meiosis

• gene mutation

  random change to the sequence of bases in DNA
• homologous pair

  2 chromosome with the same genes but different alleles (maternal & paternal chromosomes)
• what does meiosis produce

  4 haploid daughter cells that are genetically different from each other 
• how many nuclear divisions occur in meiosis

  2 nuclear divisions
• 2 types of variations that occur in meiosis

  independent segregation, crossing over
• how does independent segregation happen

  homologous chromosome arrange themselve randomly at the equator

  • this creates different combinations of chromosomes
• what is crossing over

  homologous pairs line up opposite each other at the equator, chromatids become twisted around each other

  tension between chromatids, separating chromatids and recombines with other chromosome

  • new combinations of alleles
• when does the variation occur

  both in meiosis I
• comparisions between meiosis and mitosis:

  meiosis:

  2 nuclear divisions

  forms haploid cells

  4 genetically different daughter cells formed

  mitosis:

  1 nuclear division

  forms diploid cells

  • 2 genetically identical daughter cells formed
• two forms of chromosome mutations:

  non-disjunction or polyploidy
• polyploidy

  changes in the whole set of chromosomes 
• non-disjunction

  changes in the number of individual chromosomes 

  (eg: down’s syndrome)