meiosis knowledge test

• what are the 4 stages of mitosis

  prophase, metaphase, anaphase, telophase
• what happens in prophase

  - chromosomes condense and become visible

  - centrioles separate and move to opposite poles to form spindle fibres

  - nuclear membrane breaks down and chromosomes lie free in the cytoplasm
• what happens in metaphase?

  the chromosomes become attached to the spindle by their centromere and line up along the middle of the cell. at the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle
• what happens in anaphase

  - centromeres divide, pulling apart the chromosomes

  - the spindle fibres contract pulling the chromatids to opposite ends of the cell, centromere first
• what happens in telophase

  - chromsomes reach the opposite ends and uncoil and become long and thin and invisible

  - nuclear membrane forms around each group of chromosomes to form 2 new nuclei

  - spindle fibres disintegrate
• what happens in cytokenesis

  - cytoplasm divides

  - in animals, a cleavage furrow forms to divide the cell membrane

  - two separate cells are formed
• why is meiosis needed

  production of haploid cells and genetic variation
• what does meiosis produce

  4 genetically different haploid cells
• how does genetic variation occur

  independent assortment and crossing over
• what is crossing over

  Exchange of genetic material between homologous chromosomes:

  - 2 homolygous chromosomes pair to form bivalents

  - parts of the non-sister chromatids are exchanged between the homolygous pairs

  - the tension can result in a break meaning that there is an exchange of genetic material at the chiasmata forming recombinant chromatids
• what is independent assortment

  Random distribution of homologous chromosomes:

  - homolygous pairs line up on opposite sides of the equator

  - it's random which side of the equator the paternal and maternal chromosome of each pair
• At what stage of meiosis does crossing over occur?

  Prophase 1
• what stage of meiosis does independent assortment occur

  metaphase 1
• what does a diploid cell have

  2 chromosomes of each type, one inherited from each parent - the normal chromosome number
• Where does meiosis occur?

  reproductive organs: ovaries and testes
• why is it important that meiosis produced haploid daughter cells?

  when the sperm and egg cells fuse in fertilisation, the zygote will have the normal chromosome number
• What are homologous chromosomes?

  a matching pair of chromosomes, 1 inherited from each parent: 1 paternal, 1 maternal. They have the same genes (could have different alleles), and are the same size
• in which division do homologous chromosomes separate

  meiosis 1
• which meiosis division is the reduction division and why

  meiosis 1: the chromosome number is halved
• which meiosis division is most similar to mitosis and why

  meiosis 2: the chromosomes are pulled apart
• How is recombinant DNA made by crossing over

  chromatids twist around each other and exchange equivalent sections of DNA
• how to work out the number of possible orientations of meiosis

  2^(number of chromosome pairs)
• what happens in prophase 1 of meiosis?

  chromosomes condense and become visible

  the chromosomes arrange themselves into homolygous pairs and crossing-over occurs

  centrioles move to the opposite ends of the cell forming spindle fibres

  the nuclear membrane breaks down
• what happens in metaphase 1 of meiosis?

  the homolygous pairs attach to the spindle fibres by their centromeres and line up on the middle of the cell
• what happens in anaphase 1 of meiosis?

  the spindles contract, separating the homolygous pairs - one chromosome goes to each end of the cell
• what happens in telophase of meiosis 1?

  the nuclear membrane forms around each group of chromosomes, forming 2 new nuclei
• difference between prophase in mitosis and prophase 2 in meiosis?

  in meiosis:

  • the sister chromatids aren't genetically identical
  • chromosomes are already condensed