Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number Meiosis I 1 Homologous chromosomes separate Haploid cells with replicated chromosomes Meiosis II 2 Sister chromatids separate Haploid cells with unreplicated chromosomes

Prophase I Metaphase I Anaphase I Centrosome (with centriole pair) Telophase I and Cytokinesis Prophase I Metaphase I Anaphase I Centrosome (with centriole pair) Sister chromatids remain attached Centromere (with kinetochore) Sister chromatids Chiasmata Spindle Metaphase plate Figure 13.8 The meiotic division of an animal cell Cleavage furrow Homologous chromosomes Homologous chromosomes separate Fragments of nuclear envelope Microtubule attached to kinetochore

Prophase I Metaphase I Centrosome (with centriole pair) Centromere (with kinetochore) Sister chromatids Chiasmata Spindle Metaphase plate Figure 13.8 The meiotic division of an animal cell Homologous chromosomes Fragments of nuclear envelope Microtubule attached to kinetochore

Telophase I and Cytokinesis Anaphase I Sister chromatids remain attached Figure 13.8 The meiotic division of an animal cell Homologous chromosomes separate Cleavage furrow

Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Figure 13.8 The meiotic division of an animal cell Sister chromatids separate Haploid daughter cells forming

Prophase II Metaphase II Figure 13.8 The meiotic division of an animal cell

Telephase II and Cytokinesis Anaphase II Figure 13.8 The meiotic division of an animal cell Sister chromatids separate Haploid daughter cells forming

Replicated chromosome MITOSIS MEIOSIS MEIOSIS I Parent cell Chiasma Chromosome replication Chromosome replication Prophase Prophase I Homologous chromosome pair 2n = 6 Replicated chromosome Metaphase Metaphase I Figure 13.9 A comparison of mitosis and meiosis in diploid cells Anaphase Telophase Anaphase I Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II

Figure 13.9 A comparison of mitosis and meiosis in diploid cells SUMMARY Property Mitosis Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during interphase before meiosis I begins Number of divisions One, including prophase, metaphase, anaphase, and telophase Two, each including prophase, metaphase, anaphase, and telophase Synapsis of homologous chromosomes Figure 13.9 A comparison of mitosis and meiosis in diploid cells Does not occur Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Number of daughter cells and genetic composition Two, each diploid (2n) and genetically identical to the parent cell Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes

Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Figure 13.11 The independent assortment of homologous chromosomes in meiosis Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4

Recombinant chromosomes Prophase I of meiosis Nonsister chromatids held together during synapsis Pair of homologs Chiasma Centromere TEM Figure 13.12 The results of crossing over during meiosis Anaphase I Anaphase II Daughter cells Recombinant chromosomes

Animations and Videos Meiosis Tutorial Meiosis - 1 Meiosis - 2 Stages of Meiosis Anaphase Separase Spermatogenesis Production of Male and Female Gametes Polar Body Formation

Animations and Videos Random Orientation of Chromosomes During Meiosis Independent Assortment Independent Assortment and Gamete Diversity Alleles That Do Not Assort Independently Comparison of Mitosis and Meiosis Bozeman - Diploid vs. Haploid Cells Activity- Mitosis and Meiosis Bozeman - Mitosis and Meiosis Simulation

Animations and Videos Meiosis - Nondisjunction – 1 Crossing Over Changes in Chromosome Structure The Consequence of Inversion Bozeman - Cell Cycle (Mitosis and Meiosis) X Inactivation Bozeman - X Inactivation

Animations and Videos Density-Dependent Inhibition Cytotoxic T Lymphocytes Attack a Melanoma Cell Metastasis of a Cancer Amniocentesis Animation Chorionic Villus Sampling Karyotype Animation Human Melanoma Cells Dividing Chapter Quiz Questions – 1 Chapter Quiz Questions – 2