MEIOSIS Lecture 21 Honors Biology Slide show modified
MEIOSIS Lecture #21 Honors Biology Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia
Asexual vs. Sexual Reproduction n In asexual reproduction q. One parent produces genetically identical offspring by cell division n. Ex: binary fission
ADVANTAGES OF ASEXUAL REPRODUCTION • Can make offspring faster • Don’t need a partner; only 1 “parent” needed
DISVANTAGES OF ASEXUAL REPRODUCTION • ALL ALIKE (“clones”) • Species usually CAN’T change and adapt – One disease can wipe out whole population
SEXUAL REPRODUCTION • Combines genetic material from 2 parents (sperm & egg) • Offspring are genetically different and unique from parents
ADVANTAGES OF SEXUAL REPRODUCTION • Allows for variation in population • Individuals can be different • Provides foundation for EVOLUTION • Allow species adapt to changes in their environment
EGG + SPERM If egg and sperm had same number of chromosomes as other body cells (2 n). . . baby would have too many chromosomes!
MEIOSIS is the way… to make cells with ½ the number of chromosomes; Needed for sexual reproduction http: //waynesword. palomar. edu/lmexer 2 a. htm
MEIOSIS is the way… to make cells with ½ the number of chromosomes for sexual reproduction
DIPLOID Most cells have 2 copies of each chromosome DIPLOID 2 n = _______ (one from mom; one from dad) HOMOLOGOUS CHROMOSOMES SOMATIC ) cells are diploid All BODY (____
Chromosomes that determine the sex of an organism = Sex chromosomes _________ All other chromosomes that do NOT determine autosomes gender = _____ Humans have two sex chromosomes (1 pair), which are NOT homologous 44 autosomes and _____ XX or XY
HAPLOID Some cells have only one copy of each HAPLOID 1 n chromosome = _______ All sperm and egg cells are haploid
Review…MITOSIS • Makes ___ 2 cells genetically identical _____ to parent cell & to each other 2 n • Makes ___ cells • Makes _____ SOMATIC (body) • Used by organisms to: increase size of organism, repair injuries, replace worn out cells http: //waynesword. palomar. edu/lmexer 2 a. htm
MEIOSIS 4 cells • Makes ____ genetically different from parent cell & from each other 1 n cells • Makes __________ Gametes (sperm & eggs) Sexual reproduction • Used for ______ http: //waynesword. palomar. edu/lmexer 2 a. htm
HOW IS MEIOSIS SIMILAR TO MITOSIS ? http: //highered. mheducation. com/sites/0072495855/student_view 0/chapter 28/animation__how_meiosis_w orks. html 1. Contains PMATc § Prophase, Metaphase, Anaphase & Telophase/Cytokinesis § ALL events in these phases are EXACTLY the same as mitosis 2. Uses mitotic spindle to move chromosomes 3. Daughter cells are made
HOW IS MEIOSIS DIFFERENT FROM MITOSIS ? 1. 2 divisions instead of 1 § Meiosis I and Meiosis II (PMATc I & PMATc II) 2. Synapsis & Crossing Over (PROPHASE I) 1. Independent Assortment (METAPHASE I) 2. Segregation (ANAPHASE I) 1. 4 cells are made and they are haploid 2. Daughter cells are genetically DIFFERENT 3. Different functions: § Mitosis growth, maintenance & repair
DIFFERENCE #1: 2 divisions PMATc II 2 karyokinesis (nucleus division) events occur in meiosis!
DIFFERENCE #2: Synapsis Homologous chromosomes pair up during ________ PROPHASE I called SYNAPSIS = _______ This group of FOUR (4) chromatids is called a TETRAD _________ Images modified from: http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Crossover. gif
DIFFERENCE #2: Crossing Over Exchange of DNA between homologous CROSSING OVER pairs = ________ during PROPHASE I **called genetic recombination Place(s) where crossing over happens CHIASMATA = __________ http: //highered. mcgraw-hill. com/sites/0072437316/student_view 0/chapter 12/animations. html#
DIFFERENCE #3: Independent Assortment homolgous chromosome pairs line up NEXT TO their partner at metaphase plate (Metaphase I) http: //fig. cox. miami. edu/~cmallery/150/mitosis/c 13 x 9 independent-assortment. jpg
DIFFERENCE #4: Segregation Homologous chromosome pairs separate of (chromatids do NOT separate yet…) (Anaphase I)
PHASES OF MEIOSIS Figure 11 -15 Meiosis Section 11 -4 Meiosis I = MAJOR differences from mitosis
Meiosis II: Figure 11 -17 Meiosis II NOTEno Interphase II- instead short intermission Section 11 -4 (no growth or DNA replication occurs) Same as mitosis but with HAPLOID cells Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II Anaphase II Telophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.
Ways Meiosis is different? • 2 nd and 4 th animations – http: //highered. mcgrawhill. com/sites/0072437316/student_view 0/chapter 12/an imations. html#
MAKING SPERM & EGGS
• Gametogenesis = – process of forming gametes (n) from diploid (2 n) cells 2 TYPES: • Spermatogenesis = process of forming sperm cells • After division all 4 cells undergo differentiation to become sperm cells • The cells elongate and grow tail (a flagella) • Oogenesis = process of forming ovum (egg) cell and 3 polar bodies
Starts with a 2 n cell called a GERM LINE CELL (ovary or testes)
• Sperm provides DNA to the zygote. • All the starting nutrients, organelles, molecule building blocks, etc. have to come from the ovum (egg)
OOGENESIS _________ = MAKING a MATURE EGG Produces: 1 “good” ovum (egg) 3 POLAR BODIES • CYTOPLASM DIVIDES UNEVENLY • Polar bodies are smaller and are later destroyed using APOPTOSIS
Stages of Meiosis STEP by STEP animation • http: //www. stolaf. edu/people/giannini/flashani mat/celldivision/meiosis. swf
Putting it all together… meiosis fertilization mitosis + development 46 23 egg 46 sperm 23 46 4646 46
Abnormal Chromosome Number • When nondisjunction occurs – Pairs of homologous chromosomes do NOT separate normally during meiosis • Anaphase I or Anaphase II – Gametes contain 2 copies or NO copies of a particular chromosome
What happens when meiosis goes wrong? NONDISJUNCTION!!!
Yay…The End
Meiosis Square Dance • https: //www. youtube. com/watch? v=i. CL 6 d 0 Ow. Kt 8
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