MEIOSIS http://highered.mheducation.com/sites/0072495855/student_view0/chapter3/animation__how_meiosis_works.html Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia

Asexual vs. Sexual Reproduction In asexual reproduction One parent produces genetically identical offspring by mitosis Ex: budding, binary fission, spores Parent Bud 0.5 mm

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

baby would have too many chromosomes! EGG + SPERM  If egg and sperm had same number of chromosomes as other body cells (2n) . . . baby would have too many chromosomes!

MEIOSIS is the way… to make cells (gametes) with ½ the number of chromosomes for sexual reproduction

DIPLOID HOMOLOGOUS CHROMOSOMES All BODY (________ ) cells are diploid Most cells have 2 copies of each chromosome = ______________ (one from mom; one from dad) All BODY (________ ) cells are diploid DIPLOID 2n HOMOLOGOUS CHROMOSOMES SOMATIC

Chromosomes that determine the sex of an organism = _________________ All other chromosomes that do NOT determine gender = __________ Sex chromosomes autosomes Humans have two sex chromosomes (1 pair), which are NOT homologous and _____ autosomes XX or XY 44

Sex cell has MANY chromosomes including 1 sex chromosome Sex chromosomes vs. Sex cell…NOT the same!!! X or Y= sex chromosome Sex cell has MANY chromosomes including 1 sex chromosome

HAPLOID Some cells have only one copy of each chromosome = _____________ All sperm and egg cells are haploid HAPLOID 1n

Review…MITOSIS Makes ___ cells genetically _________ to parent cell & to each other Makes ___ cells Makes __________ Used by organisms to: increase size of organism, repair injuries, replace worn out cells 2 identical 2n SOMATIC (body) http://waynesword.palomar.edu/lmexer2a.htm

MEIOSIS 4 1n Gametes (sperm & eggs) Makes ____ cells genetically different from parent cell & from each other Makes _____ cells Makes ______________ Used for ____________ 1n Gametes (sperm & eggs) Sexual reproduction http://highered.mheducation.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html http://waynesword.palomar.edu/lmexer2a.htm

WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS ? 2 divisions instead of 1 Meiosis I and Meiosis II (PMATc I & PMATc II) SYNAPSIS & CROSSING OVER (PROPHASE I) INDEPENDENT ASSORTMENT (METAPHASE I) and SEGREGATION (ANAPHASE I) 4 cells are made and they are haploid Daughter cells are genetically DIFFERENT

WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS? 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

WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS? Exchange of DNA between homologous pairs = _____________ during PROPHASE I CROSSING OVER Allows shuffling of genetic material called genetic recombination Place(s) where crossing over happens = ____________________ CHIASMATA http://highered.mheducation.com/sites/dl/free/0072835125/126997/animation5.html

Allows for_________________ in different combinations CROSSING OVER rearranging of DNA Allows for_________________ in different combinations After crossing over, chromatid arms are________________ anymore NOT IDENTICAL http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

STARTS WITH A DIPLOID (2n) CELL CALLED A “GERM LINE CELL” **only 2n cell that undergoes meiosis 2 karyokinesis events occur in meiosis!

INDEPENDENT ASSORTMENT the random alignment of homolgous chromosomes at metaphase plate (Metaphase I) http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/11_A02.swf http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg

SEGREGATION separating of doubled chromosomes (Anaphase I)

GENETIC RECOMBINATION comes from: Before gametes meet… Crossing over Segregation Independent assortment After gametes meet… Random fertilization

MITOSIS vs. MEIOSIS INTERPHASE INTERPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html 2n cell 2n cell DNA is spread out as chromatin Nuclear membrane/nucleolus visible DNA is copied during S phase Makes stuff new cell needs in G2 Cell Grows SAME AS MITOSIS

MITOSIS vs. MEIOSIS PROPHASE PROPHASE I 2n cell 2n cell DNA packs into chromosomes Nuclear membrane/ nucleolus disappear Spindle fibers appear and attach to chromosomes Centrosomes migrate to poles Same as mitosis EXCEPT: SYNAPSIS OCCURS  TETRADS FORM and CROSSING OVER OCCURS

MITOSIS vs. MEIOSIS METAPHASE METAPHASE I 2n cell 2n cell Chromosomes line up in middle in single file line Chromosomes line up in middle with homologous partner Independent assortment occurs

MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE I 2n cell 2n cell Polar fibers lengthen cell Chromatids split Polar fibers lengthen cell Chromatids stay together Homologous pairs split (SEGREATION OCCURS)

MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE I 2n cell n cell See TWO nuclei Nuclear membrane/ nucleolus return DNA spreads out as chromatin Spindle fibers disappear SAME AS MITOSIS (except haploid # of chromosomes not diploid #)

MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS I 2n cell n cell DIPLOID HAPLOID Cytoplasm splits into 2 cells using SAME AS MITOSIS (except haploid # of chromosomes not diploid #)

MITOSIS vs. MEIOSIS INTERPHASE II 2n cell n cell SKIP INTERPHASE II  RESTING PHASE INSTEAD DNA NOT COPIED BUT CENTROSOMES/CENTRIOLES ARE COPIED DNA is spread out as chromatin Nuclear membrane/nucleolus visible DNA is copied during S phase Makes stuff new cell needs in G2 Cell Grows

MITOSIS vs. MEIOSIS PROPHASE PROPHASE II n cell 2n cell DNA packs into chromosomes Nuclear membrane/ nucleolus disappear Spindle fibers appear and attach to chromosomes Centrosomes migrate to poles SAME AS MITOSIS (but cell is now HAPLOID)

MITOSIS vs. MEIOSIS METAPHASE METAPHASE II n cell 2n cell Chromosomes line up in middle in a single file line SAME AS MITOSIS (but cell is now HAPLOID)

MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE II 2n cell n cell Chromatids split and move apart SAME AS MITOSIS (but cell is now HAPLOID)

MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE II 2n cell n cell See TWO nuclei Nuclear membrane/ nucleolus return DNA spreads out as chromatin Spindle fibers disappear SAME AS MITOSIS (but cell is now HAPLOID)

MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS II RESULTS IN FOUR n cell RESULTS IN TWO 2n cell Four cells are made NOT two cells Cells are haploid NOT diploid DNA is different in all cells Cytoplasm splits

Ways Meiosis is different? Meiosis I is VERY different P1: Synapsis  Tetrad formation  Crossing over M1: Independent Assortment A1: Segregation T/C1: 2 cells are made (LIKE MITOSIS) but HAPLOID (not diploid) cells are made Meiosis II is EXACTLY the SAME as mitosis EXCEPT… Occurs in HAPLOID cells throughout the process 4 cells are made (genetically DIFFERENT

Ways Meiosis is different? 2nd and 4th animations http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html# https://www.youtube.com/watch?v=nMEyeKQClqI

MAKING SPERM & EGGS

2 TYPES: Gametogenesis = process of forming gametes (n) from diploid (2n) 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

___________________= MAKING MATURE SPERM SPERMATOGENESIS ___________________= MAKING MATURE SPERM Mature & grow flagella

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

Putting it all together… meiosis  fertilization  mitosis + development 46 46 23 46 46 46 46 46 23 46 46 egg 46 46 sperm

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!!!

Nondisjunction of sister chromatids in meiosis II Figure 15.12a, b Meiosis I Nondisjunction Meiosis II Gametes n + 1 n  1 n – 1 n –1 n Number of chromosomes Nondisjunction of homologous chromosomes in meiosis I Nondisjunction of sister chromatids in meiosis II (a) (b) http://www.sumanasinc.com/webcontent/animations/content/mistakesmeiosis/mistakesmeiosis.swf