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 (become 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
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)
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
Move the chromosomes in position for prophase and metaphase 2- NOTICE EACH CHROMOSOME IS DIFFERENT
Things to notice about the results • 4 resulting daughter cells. Contains only 1 set of genetic information in the chromosome haploidn • Each daughter cell 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