MEIOSIS. Every living cell goes through the process of mitosis……… except sex cells. There is...

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 reminderCalled gametes.Animal gametes are called...

Sperm and ovumPlant gametes are called...

Pollen grain and ovuleThese 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.

Meiosis MitosisPurpose

Where does it take place?

Produces how many cells?

What happens to the number of chromosomes?

How do parent and daughter cells differ genetically?

Is there variation between daughter cells?

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 IProphase 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.

QuestionsWhich of the following cells would be

haploid and which diploid?

White blood cellMale cell in pollen grainGuard cell (in a leaf)Root hair cellOvumSpermSkin cellEgg cell in ovule?

Where in the body of the following would you expect meiosis to be taking placeA human maleA human femaleA 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]