Mitosis Quiz copyright cmassengale 2 Name the Stages

Mitosis Quiz copyright cmassengale 2

Name the Stages of Mitosis: Early Anaphase Early prophase Metaphase Interphase Late Prophase Late telophase, Mid-Prophase Advanced cytokinesis copyright cmassengale Early Telophase, Begin cytokinesis Late Anaphase 3

Identify the Stages ? Early, Middle, & Late Prophase ? ? Metaphase Late Prophase Anaphase ? ? Late Anaphase ? Telophase copyright cmassengale ? Telophase & Cytokinesis 4

Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase Prophase copyright cmassengale 5

Uncontrolled Mitosis ü If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors ü Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell copyright cmassengale Cancer cells 6

Meiosis Formation of Gametes (Eggs & Sperm) copyright cmassengale 7

Facts About Meiosis üPreceded by interphase which includes chromosome replication üTwo meiotic divisions --- Meiosis I and Meiosis II üCalled Reduction- division üOriginal cell is diploid (2 n) üFour daughter cells produced that are monoploid (1 n) copyright cmassengale 8

Facts About Meiosis üDaughter cells contain half the number of chromosomes as the original cell üProduces gametes (eggs & sperm) üOccurs in the testes in males (Spermatogenesis) üOccurs in the ovaries in females (Oogenesis) copyright cmassengale 10

More Meiosis Facts Start with 46 double stranded chromosomes (2 n) üAfter 1 division - 23 double stranded chromosomes (n) üAfter 2 nd division - 23 single stranded chromosomes (n) ü Occurs in our germ cells that produce gametes ü copyright cmassengale 11

Why Do we Need Meiosis? üIt is the fundamental basis of sexual reproduction üTwo haploid (1 n) gametes are brought together through fertilization to form a diploid (2 n) zygote copyright cmassengale 12

Fertilization – “Putting it all together” 2 n = 6 1 n =3 copyright cmassengale 13

Replication of Chromosomes ü Replication is the process of duplicating a Occurs in Interphase chromosome ü Occurs prior to division ü Replicated copies are called sister chromatids ü Held together at centromere copyright cmassengale 14

A Replicated Chromosome Gene X Sister Chromatids Homologs (same genes, different alleles) (same genes, same alleles) Homologs separate in meiosis I and therefore different alleles separate. copyright cmassengale 15

Meiosis Forms Haploid Gametes ü Meiosis must reduce the chromosome number by half ü Fertilization then restores the 2 n number from mom from dad child too much! meiosis reduces genetic content The right number! copyright cmassengale 16

Meiosis: Two Part Cell Division Sister chromatids separate Homologs separate Meiosis II Diploid copyright cmassengale Haploid 17

Meiosis I: Reduction Division Spindle fibers Nucleus Early Prophase I (Chromosome number doubled) Late Prophase I Nuclear envelope Metaphase I Anaphase I copyright cmassengale Telophase I (diploid) 18

Prophase I Early prophase üHomologs pair. üCrossing over occurs. Late prophase üChromosomes condense. üSpindle forms. üNuclear envelope fragments. copyright cmassengale 19

Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Called Synapsis copyright cmassengale 20

Crossing-Over ü Homologous chromosomes in a tetrad cross over each other ü Pieces of chromosomes or genes are exchanged ü Produces Genetic recombination in the offspring copyright cmassengale 21

Homologous Chromosomes During Crossing-Over copyright cmassengale 22

Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by copyright cmassengale 23 independent assortment

Metaphase I Homologous pairs of chromosomes align along the equator of the cell copyright cmassengale 24

Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. copyright cmassengale 25

Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale 26

Meiosis II Gene X Only one homolog of each chromosome is present in the cell Sister chromatids carry identical genetic information. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. copyright cmassengale 27

Meiosis II: Reducing Chromosome Number Prophase II Metaphase II Telophase II Anaphase II copyright cmassengale 4 Genetically Different haploid cells 28

Prophase II Nuclear envelope fragments. Spindle forms. copyright cmassengale 29

Metaphase II Chromosomes align along equator of cell. copyright cmassengale 30

Equator Anaphase II Pole Sister chromatids separate and move to opposite poles. copyright cmassengale 31

Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale 32

Results Gametes of Meiosis (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome copyright cmassengale 33

Meiosis Animation copyright cmassengale 34

Gametogenesis Oogenesis or Spermatogenesis copyright cmassengale 35

Spermatogenesis ü Occurs in the testes ü Two divisions produce 4 spermatids ü Spermatids mature into sperm ü Men produce about 250, 000 sperm per day copyright cmassengale 36

Spermatogenesis in the Testes Spermatid copyright cmassengale 37

Spermatogenesis copyright cmassengale 38

Oogenesis üOccurs in the ovaries üTwo divisions produce 3 polar bodies that die and 1 egg üPolar bodies die because of unequal division of cytoplasm üImmature egg called oocyte üStarting at puberty, one oocyte matures into an ovum (egg) every copyright cmassengale 39

Oogenesis in the Ovaries copyright cmassengale 40

Oogenesis First polar body may divide (haploid) a X a Mitosis Oogonium (diploid) A Polar bodies die X X X Primary oocyte (diploid) Meiosis II (if fertilization occurs) A X Secondary oocyte (haploid) copyright cmassengale Ovum (egg) A Mature egg X Second polar body (haploid) 41

Comparing Mitosis and Meiosis copyright cmassengale 42

Comparison of Divisions Mitosis Number of divisions Number of daughter cells Genetically identical? 1 Meiosis 2 2 4 Yes No Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and copyright cmassengale repair Sexual reproduction 43 Chromosome #