Meiosis (AQA AS Biology): Revision Note

Meiosis

• Meiosis produces daughter cells that are genetically different from each other and to the parent cell

• This is due to the processes of independent segregation and crossing over

Independent segregation

• The independent segregation of homologous chromosomes leads to genetically different daughter cells

• This happens during meiosis:

  • Meiosis is the process that forms gametes (sperm or egg), and it has two divisions: meiosis I and meiosis II

• During meiosis I, homologous chromosomes line up in the centre of the cell

• The chromosomes are then separated and pulled into different cells — this is called segregation of homologous chromosomes

• Each pair of homologous chromosomes lines up randomly

  • That means the way one pair segregates does not affect how another pair segregates

  • This is what makes it independent — each chromosome pair has its a different path by chance

Crossing over

• Crossing over is the process where homologous chromosomes exchange genetic material during meiosis I

• This process results in further genetic variation among daughter cells

• Homologous chromosomes pair up and form bivalents

• The chromatid then breaks and rejoins to the chromatid of its homologous chromosome, so that its alleles are exchanged

• Crossing over leads to new combinations of alleles on each chromatid; this is called recombination