meiosis. why meiosis? meiosis is a form of cell division that produces haploid cells. a haploid cell...
TRANSCRIPT
MEIOSIS
Why Meiosis?• Meiosis is a form of cell division that produces
haploid cells.• A haploid cell contains one full set of chromosomes.
In human, the haploid cells are the sex cells – sperm & egg – which contain 23 chromosomes.
• Sex cells = gametes = germ cells.• A regular body cell is a diploid cell that contains two
full sets of chromosomes – one from mom and one from dad. The number of chromosomes in a human diploid cell is 46 (2 x 23).
• Meiosis uses diploid body cells to create the haploid sex cells and, for this reason, is known as reduction division.
Meiosis – Same But Different• Meiosis has some similarities to mitosis in
terms of the actions and movement of the chromosomes within the cell.
• The main difference between meiosis and mitosis is that meiosis has two rounds of division and creates four haploid sex cells while mitosis has only one round of division and gives way to two identical, diploid, daughter cells.
The Stages of Meiosis• The names of the stages of meiosis are the
same as those of mitosis except that there are two rounds of division so you must indicate which division (I or II) you are dealing with.
• This means that you have Prophase I in the first round of division and Prophase II in the second.
• Overall…InterPIMIAITIPIIMIIAIITIIInter
Interphase Prophase I
• DNA as chromatin.• Nucleus in place.• Centrioles present but
not at poles.• Nucleolus present.
• DNA = chromosomes.• Chromosomes in groups of
four called tetrads.• Nucleus dissolving.• Centrioles migrating to the
poles of the cell.
Metaphase I Anaphase I
• Centrioles at poles of cell.
• Spindle formed – microtubules attached to tetrads.
• Nucleus gone.
• Tetrads are pulled apart. (4 2 pairs)
Telophase I Prophase II
• Chromosomes pairs are at opposite ends of cells.
• Cytokinesis takes place.
• Cytokinesis is complete.
• Centrioles migrate to opposite poles.
Metaphase II Anaphase II
• Chromosome pairs line up in middle of cell.
• Centrioles are at poles of cell and form the spindle.
• Chromosome pairs are pulled apart and moved to opposite ends of cell.
Telophase II Sex Cells
• Nucleus begins to reform.
• Cytokinesis takes place.
• Four haploid sex cells.• Remember…
Sex cells = gametes = germ cells
Meiosis Overall
Males vs. FemalesMEN
• Spermatogenesis• Starts at puberty• Testes• Four sperm cells
• Can produce sperm until death
WOMEN• Oogenesis• Starts at puberty• Ovaries• One egg & three
polar bodies• Stops at menopause
Males vs. Females
Meiosis vs. Mitosis
Meiosis vs. MitosisMEIOSIS
• Sex cells• Two rounds of
division• Haploid cells• Results in four cells• Genetically
different• Tetrads present
MITOSIS• Body cells• One round of
division• Diploid cells• Results in two cells• Genetically
identical• No tetrads here
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