meiosis

• what is meiosis needed for?

  sexual reproduction
• why is meiosis needed for sexual reproduction?

  because it produces daughter cells (gametes) with half the number of chromosomes of the parent cell
• What happens before meiosis starts?

  The DNA unravels and replicates so there are two copies of each chromosome, called CHROMATIDS
• What happens after DNA replication ?

  The DNA condenses to form double-armed chromosomes, each made from two sister CHROMATIDS that are joined in the middle by a CENTROMERE
• What happens after the DNA condenses?

  meiosis 1 (First division) - the chromosomes arrange themselves into homologous pairs
• what happens after meiosis 1?

  the homologous pairs are then separated , halving the chromosome number
• what happens after the homologous chromosomes are separated?


  meiosis II (second division)- the pairs of sister chromatids that make up each chromosome are separated (the CENTROMERE is DIVIDED)
• What happens after meiosis II?

  Four haploid cells (gametes) that are genetically different from each other are produced
• the chromosomes that make up each pair are the same size and have the same genes although they could have different versions of these genes (alleles) . These pairs of chromosomes are called homologous pairs.
• What does meiosis produce?

  Daughter cells that are genetically different from each other
• What does crossing over between chromosomes usually result in?

  further genetic variation between daughter cels
• What do two nuclear divisions usually result in?

  formation of 4 haploid daughter cells from a single diploid parent cell
• What do genetically different daughter cells result from?

  The independent segregation of homologous chromosomes
• where does meiosis occur?

  reproductive organs
• What are cells that divide by meiosis like to start with?

  Diploid to start with , but the cells formed from meiosis are haploid- the chromosome number halves
• Describe homologous pairs of chromosomes?

  the chromosomes that make up each pair are the same size and have the same genes , although they could have different versions of those genes (ALLELES)
• what happens to chromosome number during the 1st division?

  Halved