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MEIOSIS http://waynesword.palomar.edu/lmexer2a.htm Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS REPRODUCE ALL LIVING THINGS __________ ASEXUAL Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm Family http://babyhearing.org/Parenet2Parent/index.asp SEXUAL ASEXUAL REPRODUCTION Bacteria reproduce using http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html BINARY FISSION __________________________________ http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.13.2.hydra.jpg Budding & regeneration are used by plants and animals to reproduce asexually (mitosis) Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm BINARY FISSION & MITOSIS identical Produces cells that are __________ copies of parent cell ADVANTAGES OF ASEXUAL REPRODUCTION Can make offspring faster Don’t need a partner http://www.mrgrow.com/images/cutting.jpg DISVANTAGES OF ASEXUAL REPRODUCTION ALL ALIKE Species CAN’T change and adapt One disease can wipe out whole population http://www.mrgrow.com/images/cutting.jpg SEXUAL REPRODUCTION Family image from: http://babyhearing.org/Parenet2Parent/index.asp Combines genetic material from 2 parents (sperm & egg) Offspring are genetically different 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 http://naturalsciences.sdsu.edu/classes/lab8/spindex.html Image by Riedell EGG Image by Riedell + http://www.angelbabygifts.com/ SPERM If egg and sperm had same number of chromosomes as other body cells . . . baby would have too many chromosomes! http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg MEIOSIS is the way… http://waynesword.palomar.edu/lmexer2a.htm to make cells with ½ the number of chromosomes for sexual reproduction DIPLOID & HAPLOID Most cells have 2 copies of each chromosome DIPLOID 2n = ______________ (one from mom; one from dad) HOMOLOGOUS CHROMOSOMES All BODY (___________) = SOMATIC cells are diploid Chromosomes that determine the sex of an organism = _________________ Sex chromosomes http://www.angelbabygifts.com/ All other chromosomes = _________________ autosomes Humans have two sex chromosomes X y and _____ 44 autosomes KARYOTYPE is a picture of A __________ an organism’s chromosomes DIPLOID & HAPLOID Some cells have only one copy of each HAPLOID 1n chromosome = _____________ All sperm and egg cells are haploid MITOSIS • Makes ___ 2 cells genetically identical _________ to parent cell & to each other 2n • Makes ___ cells • Makes __________ SOMATIC (body) • Used by organisms to: increase size of organism, repair injuries, replace worn out cells http://waynesword.palomar.edu/lmexer2a.htm MEIOSIS 4 cells • Makes ____ genetically different from parent cell & from each other 1n cells • Makes _____ • Makes ______________ Germ cells OR Gametes (sperm & eggs) • Used for ____________ sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm What Makes Meiosis Different? Meiosis Lecture 2 WHAT MAKES MEIOSIS DIFFERENT ? 1. SYNAPSIS & CROSSING OVER (PROPHASE I) 2. SEGREGATION & INDEPENDENT ASSORTMENT (ANAPHASE I) 3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE WHAT MAKES MEIOSIS DIFFERENT ? 1. Homologous chromosomes pair up during ________________ PROPHASE I SYNAPSIS = ______________ This group of FOUR (4) chromatids is called a TETRAD _________________ Images modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif WHAT MAKES MEIOSIS DIFFERENT? 1. Exchange of DNA between OVER homologous pairs = CROSSING _____________ during PROPHASE I Allows shuffling of genetic material Places where crossing over happens CHIASMATA = ____________________ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif HOMOLOGOUS CHROMOSOMES Image modified by Riedell • SAME SIZE • SAME SHAPE • CARRY GENES for the SAME TRAITS IDENTICAL • BUT NOT ______________! (Don’t have to have the SAME CHOICES) http://sps.k12.ar.us/massengale/genetics%20tutorial.htm Image modified by Riedell CROSSING OVER rearranging of DNA • Allows for_________________ in different combinations • After crossing over, chromatid arms NOT IDENTICAL anymore are________________ http://sps.k12.ar.us/massengale/genetics%20tutorial.htm SEGREGATION (Anaphase I) • Orientation of the chromosome pairs is random with respect to the poles • Separation of homologous chromosomes ensures that each gamete receives a haploid set of chromosomes composed of both maternal and paternal chromosomes SEGREGATION & CROSSING OVER together make even more combinations See an animation http://waynesword.palomar.edu/lmexer2a.htm INDEPENDENT ASSORTMENT http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg INDEPENDENT ASSORTMENT at ANAPHASE I Lots of different combinations are possible! This is why you don’t look exactly like your brothers and sisters even though you share the same parents! GENETIC RECOMBINATION comes from: • • • • Crossing over Segregation Independent assortment Random fertilization – fusion of two gametes, increase genetic variation in populations by providing new combinations of genetic information in the zygote, and restores diploid number of chromosomes Phases of Meiosis Figure 11-15 Meiosis Section 11-4 Meiosis I Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Telophase II Meiosis II results in four haploid (N) daughter cells. MITOSIS vs MEIOSIS INTERPHASE INTERPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html • DNA is spread out as chromatin • Nuclear membrane/ nucleolus visible • DNA is copied during S phase • Makes stuff new cell needs in G2 SAME AS MITOSIS MITOSIS vs MEIOSIS PROPHASE PROPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/ spindle fibers appear DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/ spindle fibers appear Homologous pairs match up MITOSIS vs MEIOSIS METAPHASE METAPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html • Chromosomes line up in middle Chromosomes line up in middle with homologous partner MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html APART: Chromatids split APART: Chromatids stay together Homologous pairs split MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html See TWO nuclei Nuclear membrane/ SAME AS MITOSIS nucleolus return DNA spreads out as chromatin Spindle/centrioles disappear MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I http://www.pbs.org/wgbh/nova/baby/divi_flash.html Cytoplasm splits into 2 cells SAME AS MITOSIS MITOSIS vs MEIOSIS INTERPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html • DNA is spread out as chromatin SKIP • Nuclear membrane/ INTERPHASE II nucleolus visible • DNA is copied during S phase DNA NOT COPIED MITOSIS vs MEIOSIS PROPHASE PROPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html • DNA scrunches into chromosomes • Nuclear membrane/ nucleolus disappear • Centrioles/ spindle fibers appear SAME AS MITOSIS MITOSIS vs MEIOSIS METAPHASE METAPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html • Chromosomes line up in middle SAME AS MITOSIS MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Chromatids split and move apart SAME AS MITOSIS MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Two nuclei Nuclear membrane/ nucleolus returns Centrioles/spindle fibers disappear DNA spreads out as chromatin SAME AS MITOSIS MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Cytoplasm splits http://www.pbs.org/wgbh/nova/baby/divi_flash.html SAME AS MITOSIS Ways Meiosis is different? • Homologous pairs match up & trade DNA (SYNAPSIS & CROSSING OVER) in PROPHASE I •SEGREGATION & INDEPENDENT ASSORTMENT in Anaphase I create genetic recombination • Skipping INTERPHASE II(Dividing TWICE but copying DNA once) produces 1n cells Nondisjunction – Failure of homologous chromosomes OR chromatids to separate at anaphase Mistakes in Meiosis Meiosis Lecture 4 Nondisjunction Results in ANEUPLOIDY = one or more chromosomes have extra or missing copies AFTER FERTILIZATION: Cell with only 1 copy of a chromosome instead of 2 = MONOSOMY Cell with 3 copies of a chromosome instead of 2 = TRISOMY • Errors in mitosis or meiosis can result in changes in phenotype – Changes in chromosome number often result in: • New phenotypes – Sterility caused by triploidy and increased vigor of other polyploids • human disorders with developmental limitations – Trisomy 21 (Down syndrome) – XO (Turner Syndrome) Karyotype can show: • • • • Sex of baby Missing or extra chromosomes Major deletions or translocations Can’t see individual gene changes http://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Dow Down syndrome (Trisomy 21) Most common chromosomal http://www.hadsa.org/ abnormality (1 in 800 births) Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation 50% have heart defects that need surgery to repair Both older (35+ years) and younger (under 16 years) mothers are more at risk. Some individuals with Down syndrome have the normal number of chromosomes but have all or part of a third chromosome 21 attached to another chromosome by translocation. http://content.answers.com/main/content/wp/en/thum Turner syndrome (X0) http://medgen.genetics.utah. 1 in 5000 births Females have only one X chromosome Small size Broad chest Slightly decreased intelligence 35% have heart abnormalities Hearing loss common Reproductive organs don’t develop at puberty Klinefelter syndrome http://www.akdeniz.edu.tr/tip/histoloji/ 1 in 2000 births live births Males have extra X chromosomes (Can be XXy, XXXy, or XXXXy) Taller than average Normal intelligence have male sex organs, but are sterile. may be feminine characteristics, Often not discovered until puberty when don’t mature like peers Presence of BARR BODIES