Presentation on theme: "Cell Divison. Each of your body cells has 46 chromosomes, or 23 pairs. Each pair is made of HOMOLOGOUS CHROMOSOMES Homo = same These chromosomes contain."— Presentation transcript:
When your BODY cells (autosomal) divide, they make exact copies Results = two cells with the same type and number of chromosomes as the parent cell. Many animals reproduce ASEXUALLY – through mitosis ex: flatworms, sponges, jellyfish
If humans were created through mitosis: 1 st generation 46 from mom + 46 from dad = 92 chromosomes for baby then 2 nd generation 92 from mom + 92 from dad = 184 chromosomes for baby And so on, and so on, and so on…
A second type of cell division that occurs in the SEX CELLS (gametes: sperm and egg) Division creates four cells with half the number of chromosomes as the parent cell.
Body cells (autosomal cells) are DIPLOID DI = 2; Each cell has 2 copies of each chromosome These are considered “2n” ◦ “n” is the chromosome number Sex cells are HAPLOID Each sex cell has HALF the normal number of chromosomes These are considered “n”
Sperm are the sex cells in males Eggs are the sex cells in females Both are produced through MEIOSIS Any reproduction that involves SPERM and EGGS is considered SEXUAL REPRODUCTION.
Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II First Division Second Division **Meiosis contains TWO divisions whereas Mitosis only has one! ** Similar to Mitosis…Meiosis does experience interphase. **Chromosomes are replicated during “S” phase.
Prophase I Chromatin coil and condense, chromosomes are visible. Spindle form Homologous chromosomes line up gene by gene to form a tetrad. ◦ Tetrad: two homologous chromosomes made of two sister chromatids paired tightly ◦ Crossing over occurs.
Occurs between two non-sister chromatids. Can happen many times or not at all Average: 2 to 3 crosses per each pair of homologues. Results in genetic variation ◦ Explains why siblings look alike but not identical.
Interphase: All 23 pairs of chromosomes duplicate. Prophase begins.
Metaphase I ◦ Spindle fibers attach to centromere of each chromosome. ◦ Tetrads pulled to the center ◦ Line up beside each other In Mitosis they line up end to end…not paired.
Meiosis: Chromosome line up beside their homologous pairs. Mitosis: Chromosomes line up end to end
Anaphase I Homologous chromosomes separate ◦ Head to opposite sides of cell Centromeres do not split ◦ Unlike mitosis Ensures that each new cell will receive one chromosome from each homologous pair
Meiosis: Sister Chromatids stay together Mitosis: Sister Chromatids separate
Telophase I Prophase Reversed Cytokenisis Occurs Still has one chromosome from each homologous pair Start the division process over again!
Meiosis: Still have one chromosome from each homologous pair **need to separate them in order for each sex cell to have ½ of the genetic material.
Prophase II Chromosomes Condense Spindle Form and attach to centromere ◦ NOTICE….did not undergo inerphase therefore the chromosomes did not replicate again! Metaphase II ◦ Chromosomes line up at the equator End to end this time….like mitosis Anaphase II ◦ Sister chromatids split apart and move to opposite poles Telophase II ◦ Nuclei reform ◦ Spindle Breaks down Cytokenisis