Meiosis Objectives 1 To Compare Mitosis with Meiosis

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 u IPMAT

Big Events of Mitosis u u u u u 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 opposite sides of the cell. Telophase: “Opposite” of Prophase Cytokinesis Mitosis Review Mitosis Rap. . . You Have to See This

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

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

From Zygote to Embryo Zygote 2 n 2 n

From Zygote to Embryo Cleavage

From Zygote to Embryo Blastula

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

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

Synapsis u Animation u Chromatid pairs join to form Tetrads u 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. u Increases genetic diversity in sex cells u

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

Metaphase I u Tetrads align at the equator of the spindle.

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

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

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

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

Metaphase II u Chromatids align at the equator of the spindle

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

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

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

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

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

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

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

Spermatogenesis vs Oogenesis u Spermatogenesis u Oogenesis

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

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

Chromosome Number Disorders u Trisomy 21 – Down Syndrome

Chromosome Number Disorders u Trisomy 18 – Edward’s Syndrome

Chromosome Number Disorders u Trisomy xxy – Kleinfelters Syndrome

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

Down Syndrome u u u u Welcome To Holland by Emily Perl Kingsley © 1987 by Emily Perl Kingsley. All rights reserved. Article printed with permission of the author. I am often asked to describe the experience of raising a child with disability - to try to help people who have not shared that unique experience to understand it, to imagine how it would feel. It's like this. . . When you're going to have a baby, it's like planning a fabulous vacation trip - to Italy. You buy a bunch of guide books and make your wonderful plans. The Coliseum. The Michelangelo David. The gondolas in Venice. You may learn some handy phrases in Italian. It's all very exciting. After months of eager anticipation, the day finally arrives. You pack your bags and off you go. Several hours later, the plane lands. The stewardess comes in and says, "Welcome to Holland. " "Holland? !? " you say. "What do you mean Holland? ? I signed up for Italy! I'm supposed to be in Italy. All my life I've dreamed of going to Italy. " But there's been a change in the flight plan. They've landed in Holland there you must stay. The important thing is that they haven't taken you to a horrible, disgusting, filthy place, full of pestilence, famine and disease. It's just a different place.

Down Syndrome u u u u So you must go out and buy new guide books. And you must learn a whole new language. And you will meet a whole new group of people you would never have met. It’s just a different place. It's slower-paced than Italy, less flashy than Italy. But after you've been there for a while and you catch your breath, you look around. . and you begin to notice that Holland has windmills. . and Holland has tulips. Holland even has Rembrandts. But everyone you know is busy coming and going from Italy. . . and they're all bragging about what a wonderful time they had there. And for the rest of your life, you will say "Yes, that's where I was supposed to go. That's what I had planned. " And the pain of that will never, ever go away. . . because the loss of that dream is a very significant loss. But. . . if you spend your life mourning the fact that you didn't get to Italy, you may never be free to enjoy the very special, the very lovely things. . . about Holland. * * *