Meiosis Objectives: 1. To Compare Mitosis with Meiosis 2. To recognize the mechanisms of Meiosis that increase genetic diversity. 3. To understand the effects of abnormal Meiosis

Mitosis Review IPMAT

Big Events of Mitosis Interphase: DNA replicates Prophase: Chromatid pairs form Nuclear envelope disappears. Spindle forms Metaphase: Chromatid pairs align at the equator of the spindle. Anaphase: Chromatid pairs separate and Chromosomes are pulled to 0pposite sides of the cell. Telophase: “Opposite” of Prophase Cytokinesis Mitosis Review Mitosis Rap.....You Have to See This

Reasons for Mitosis? Production of 2 daughter cells that are genetically identical Provides a) a means of asexual reproduction for unicellular organisms b) replacement of worn out and damaged cells c) growth of an organism

Replication Chromosomes, Chromatids and Centromeres Centromere Chromosome arm Identical chromatid Chromatid Anaphase A packaged chromosome Two identical chromosomes

From Zygote to Embryo Zygote 2n Zygote 2n

Cleavage From Zygote to Embryo

Cleavage From Zygote to Embryo

Cleavage From Zygote to Embryo

Cleavage From Zygote to Embryo

Blastula From Zygote to Embryo

Meiosis Special cell division that produces “haploid” sex cells or gametes. Consists of 2 stages, Meiosis I and Meiosis II One replication and two cell divisions For every special reproductive cell (germ cell) that undergoes Meiosis, four haploid sex cells are produced

Meiosis I Interphase I - DNA Replicates(This cell: 2n = 4) Prophase I – Nuclear envelope disappears – Replicated Chromatin coils into chromatid pairs – Spindle forms – Synapsis forms Tetrads

Synapsis Animation Chromatid pairs join to form Tetrads After tetrad formation, arms of the chromatid pairs exchange segments in a process called Crossing Over

Crossing over Where the chromatid pairs cross over is called the Chiasma. Increases genetic diversity in sex cells

Prophase I: Tetrad formation/ crossing over Prophase I: Tetrad formation/ crossing over Crossing Over Anaphase I Telophase II Metaphase I Telophase I Because of crossing over, every gamete receives a unique set of genetic information.

Metaphase I Tetrads align at the equator of the spindle. Note: These tetrads should still be connected!!

Anaphase I Tetrads separate in an event called Disjunction. Chromatid pairs are pulled to opposite sides of the cell

Telophase I Cytokinesis splits the cell in two and ends Meiosis I

Meiosis II Cells skip Interphase II and move right into Prophase II Meiosis II follows the stages of Mitosis

Prophase II Nuclear envelope disappears Spindle forms Chromatids are floating throughout the cytoplasm

Metaphase II Chromatids align at the equator of the spindle

Anaphase II Chromatid pairs split and chromosomes are pulled to opposite sides of the cells

Telophase II Cytokinesis splits the 2 cells into 4 Haploid sex cells. (n=2)

Interphase Mother cell Stages Of Meiosis: Meiosis I Meiosis II Prophase I: Tetrad formation/ crossing over Prophase I: Tetrad formation/ crossing over Metaphase I Telophase I Prophase I: Condensing Chromosomes Prophase I: Condensing Chromosomes Anaphase I

Telophase I Stages Of Meiosis: Meiosis II Metaphase II Anaphase II Telophase II The products of mitosis are 2 diploid cells with identical chromosomes. The products of meiosis are 4 haploid cells each with a unique set of chromosomes. Prophase II

Meiosis Review Meiosis Meiosis 2 (The quiz) Meiosis 2 Meiosis in a 2n = 2 Cell Meiosis and Crossing Over Here it is! Another look! Meiosis Square Dance

Spermatogenesis vs Oogenesis Spermatogenesis - produces sperm cells - ratio of germ cells to sex cells is 1:4 Oogenesis - produces egg cells - ratio of germ cells to sex cells is 1:1 (3 “polar bodies die each time)

Spermatogenesis vs Oogenesis Spermatogenesis Oogenesis

Terms to Remember: Synapsis Tetrads Crossing Over Disjunction Spermatogenesis Oogenesis Germ Cells Haploid Diploid

Meiosis Dry Lab Using a special germ cell with a 2n = 6, draw the stages of Meiosis I and Meiosis II as a review of this special cell division. Draw your diagrams neatly. Make sure any important structures or events are clearly labelled. Your finished review will go in your lab book. I will provide paper and “cell simulators”

Nondisjunction Occasionally, during Anaphase I, the tetrads do not separate in an event called Nondisjunction. The result is sex cells with either 1 extra chromosome or 1 less chromosome

Nondisjunction An extra chromosome creates a Trisomy (3 chromosomes where there should be 2) One less chromosome creates a Monosomy (1 chromosome where there should be 2)

Chromosomes Autosomal Chromosomes – Chromosomes other than sex chromosomes – Homologous – same size, shape and have the same gene arrangement – Pairs 1-22 in humans – Pairs 1-3 in fruit flies

Sex Chromosomes – Homologous in females XX – Non-homologous in males XY – SRY Gene found on the Y chromosome directs the development of a male.

Chromosomal Disorders Autosomal Disorders: – Down Syndrome (Trisomy 21) – Edward’s Syndrome (Trisomy 18) – Patau’s Syndrome (Trisomy 13) Sex Chromosome Disorders: – Turner’s Syndrome (X0) – Kleinfelter’s Syndrome (XXY)

Chromosome Number Disorders Trisomy 21 – Down Syndrome

Chromosome Number Disorders Trisomy 18 – Edward’s Syndrome

Chromosome Number Disorders Trisomy xxy – Kleinfelters Syndrome

Chromosome Number Disorders Monosomy xo – Turners Syndrome (single x female)

Abnormal Chromosomal Number Disorders Turner's Syndrome Edwards Syndrome Elliott Edwards SyndromeElliott Patau's Syndrome Down Syndrome Kleinfelters Syndrome Angelman Syndrome