Meiosis
Why Do cells Go through Meiosis? Cells go through Meiosis in order to make Sex Cells Sex cells are also called Gametes Four Daughter Cells are created Haploid (1N)
Interphase Cell Grows Duplicates DNA Cell Prepares to divide
After Interphase In order to make sex cells or cells with half the number of chromosomes meiosis has TWO phases Meiosis I and Meiosis II
Prophase I Chromosomes Condense (visible) Homologous chromosomes form a tetrad (4 chromatids)- paring up called SYNAPSIS Crossing Over Occurs
Crossing Over Homologous Chromosomes- Similar chromosomes and genes in the same location, but come from different parents When the chromosomes touch they switch genetic information CROSSOVER Causes genetic variation in the resulting gametes
Knowledge Check Why do cells go through meiosis? A- to replicate body cells B- To replicate sex cells What’s the name of the type of cell formed through meiosis? A- gametes B- somatic cells What important event leads to genetic variation? A- homologous chromosomes B- Tetrad C-Crossover
Crossover close-up with results
Metaphase I Homologous chromosomes move together to the middle of the cell Spindle attaches to the centromere
Anaphase I Homologous chromosomes separate Sister chromatids stay attached Move towards opposite poles
Telophase I Division of cytoplasm Creates Two daughter cells Begin Meiosis II There is a brief interphase, but no DNA replication Why?
Knowledge Check During Anaphase I in meiosis: A- The sister chromatids separate to opposite poles B- The homologous chromosomes separate to opposite poles Name the stage
Prophase II Spindles re-appear Nuclear membrane stays separated
Metaphase II Chromosomes line up in the middle Spindle attaches How are metaphase I and II different?
Anaphase II Sister Chromatids Separate from each other How are Anaphase I and II different from eachother?
Telophase II Nucleus reforms Division into four daughter cells Haploid (1N) Gametes (egg and sperm)
Knowledge Check- Name the phase
Final Results of Meiosis 4 haploid daughter cells which will develop into sex cells Each daughter cell has half of the genetic information of a somatic cell 23 chromosomes for each sex cell NOTE: Males will create 4 sperm cells for every one cell that goes through meiosis Females will create 4 egg cells, BUT 3 will turn into non usable polar bodies and 1 will mature into an egg cell.
Let’s watch Meiosis in Motion http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit3/bio_ch06_0175_ab_meiosis.html http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
Through sexual reproduction and fertilization, these gametes fuse to form one diploid cell again (2n 46 chromosomes).
Zygote= a fertilized egg Zygote will begin to rapidly mitotically divide to make more cells to form a BLASTOCYST and then develop into an EMBRYO.
Fertilization and Life http://glencoe.mcgraw-hill.com/sites/dl/free/0078617022/161752/00053403.html
Clay meiosis As a class we will use the clay, yarn, and string to go through the phases of meiosis so that you can visually see what happens
Create Prophase 1 with your clay and yarn- SHOW CROSSOVER
Create metaphase 1 with your clay and yarn
Create anaphase 1 with your clay and yarn
Create Telophase 1 with your yarn and clay
Move the chromosomes in position for prophase and metaphase 2- NOTICE EACH CHROMOSOME IS DIFFERENT
Position the chromosomes, spindle fibers, and centrioles to anaphase II
Position your chromosomes for telophase and cytokinesis
Things to notice about the results 4 resulting daughter cells. Contains only 1 set of genetic information in the chromosome haploidn Each daughter cell is contains chromosomes that are genetically different from one another These daughter cells will develop into full sex cells (gametes). Sperm for males and egg for female