9.2 - Meiosis + genetic variation

• What does meiosis produce ?

  4 daughter cells that are genetically different form each other
• Do the daughter cells have the same no. of chromosomes as the parent cell after meiosis ?


  No, they have half the no. of chromosomes as the parent cell
• Are gametes diploid or haploid ?


  Haploid
• How many nuclear divisions happen in meiosis ?

  2
• What occurs in the first division of meiosis (meiosis 1) ?

  Homologous chromosomes pair and line up at equator and their chromatids wrap around each other (crossover can occur), the homologous pairs separate and 1 chromosome from each pair goes into 1 of 2 daughter cells
• What process that increases genetic variation can occur in M1 ?

  Crossover
• What occurs in the 2nd meiotic division (M2) ?

  The sister chromatids are separated into 4 cells each with a single chromatid
• What 2 things can occur during meiosis that increases genetic variation ?

  Independent segregation of homologous chromosomes, crossing over between homologous chromosomes
• Definition of homologous chromosomes ?

  A pair of Chromosomes, one maternal and one paternal, that have the same gene loci
• What’s independent segregation ?

  The random arrangement of Chromosomes in M1, determines which chromosome from the pair goes into the daughter cell
• What’s recombination ?


  After crossover has occurred between homologous pairs, the broken off portions of chromatids recombine with another chromatid
• How does random fertilisation of haploid gametes increase genetic variation ?

  Gametes come from different parents so two different genetic make ups are combined
• How many different types of cell are produced if crossing over and recombination don’t occur ?

  Only 2
• 2 ways that genetic variation is increases that aren’t caused by meiosis ?

  Spontaneous base mutations, random fertilisation of gametes
• Formula to discover the number of possible combinations of chromosomes for each daughter cell ?

  2^n , n = no. of pairs of homologous chromosomes
• Formula to discover the no. of different chromosome combinations in an offspring as a result of sexual reproduction ?

  (2^n)^2 , n= no. of pairs of homologous chromosomes