MEIOSIS

Every living cell goes through the process of mitosis……… except sex cells. There is always one exception to biological rule!

Mitosis Reminder

Sex Cells reminder Called gametes. Animal gametes are called... Sperm and ovum Plant gametes are called... Pollen grain and ovule These four cells have half the number chromosomes as the body cells. If there is a full set of chromosomes we say it has a diploid set. If there are half the number of chromosomes in the nucleus than we say it has a haploid set.

Spot the Difference! Using your mitosis/meiosis sheet, identify as many of the biological differences between the flow diagrams.

Which are in a diploid state and which are in a haploid state?

We also call it reduction division, can you see why?

Stages of Meiosis I Prophase I: Chromatin shortens and thickens, and chromosomes appear. The chromosomes will replicate at this stage (although separate chromatids cannot yet be seen). Homologous chromosomes match up and crossing- over occurs. Metaphase I: Random assortment occurs; homologs line up on equator.

Anaphase I: Each homologue separates and moves to opposite poles of the cell; being pulled by the spindle fibres. Telophase I: New nuclear membranes form Chromosomes decondense Cytoplasm divides (cytokinesis).

Prophase II: Nuclear membranes break down Chromosomes shorten and thicken Centrioles move to poles Spindle fibres form. Metaphase II: Chromosomes line up along equator, not in homologous pairs. Stages of Meiosis II

Anaphase II: Each sister chromatid is separated at the centromere, and they move to opposite poles of the cells. Telophase II: Nuclear membrane reforms Chromosomes uncoil and lengthen Spindle disappears Nuclear envelopes reform. Cytoplasm divides in cytokinesis; 4 haploid daughter cells (gametes) are formed.

Questions Which of the following cells would be haploid and which diploid? White blood cell Male cell in pollen grain Guard cell (in a leaf) Root hair cell Ovum Sperm Skin cell Egg cell in ovule?

Where in the body of the following would you expect meiosis to be taking place A human male A human female A flowering plant? Why are organisms produced by asexual reproduction identical to each other?

Mitosis and Meiosis True or false?

Mitosis is necessary for growth, repair and replacement of tissues True – it is the process by which body cells divide to make new cells.

In meiosis the number of chromosomes stays the same False – in meiosis the number of chromosomes is halved.

Meiosis takes place in the testes True – it also takes place in the ovaries.

Mitosis involves two divisions of chromosomes False – mitosis involves one division of chromosomes.

Mitosis results in genetically identical cells True

Mitosis is known as the reduction division False – meiosis is known as reduction division. [Higher]