MEIOSIS Chapter 12 Honors Genetics Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia

BINARY FISSION & MITOSIS Produces cells that are genetically __________ copies of parent cell identical

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

+ 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 with ½ the number of chromosomes for sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm

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

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://waynesword.palomar.edu/lmexer2a.htm

2 karyokinesis events occur in meiosis!

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 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? 1. 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.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.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

INDEPENDENT ASSORTMENT the random alignment of homolgous chromosome pairs at metaphase plate (Metaphase I) http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg

SEGREGATION separating of doubled chromosomes (homologous pairs) (Anaphase I)

SEGREGATION & CROSSING OVER together make even more gamete combinations See an animation http://waynesword.palomar.edu/lmexer2a.htm

INDEPENDENT ASSORTMENT and SEGREGATION at METAPHASE/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! 3rd animation http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

GENETIC RECOMBINATION comes from: Crossing over Segregation Independent assortment Random fertilization

PHASES OF MEIOSIS Meiosis I = MAJOR differences from mitosis Figure 11-15 Meiosis Section 11-4 Meiosis I = MAJOR differences from mitosis

Meiosis II: NOTE- no Interphase II- instead short intermission (no growth or DNA replication occurs) Figure 11-17 Meiosis II Section 11-4 Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. 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.

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 DNA packs into chromosomes Nuclear membrane/ nucleolus disappear Spindle fibers appear and attach to chromosomes Centrosomes migrate to poles SYNAPSIS 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

MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS I 2n cell n cell DIPLOID HAPLOID Cytoplasm splits into 2 cells using SAME AS MITOSIS

MITOSIS vs. MEIOSIS INTERPHASE II 2n cell n 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 SKIP INTERPHASE II DNA NOT COPIED

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 SAME AS MITOSIS (but cell is now HAPLOID) Cytoplasm splits http://www.pbs.org/wgbh/nova/baby/divi_flash.html

Ways Meiosis is different? 2nd and 4th animations http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

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

Starts with a 2n cell called a GERM LINE CELL

___________________= 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

Stages of Meiosis STEP by STEP animation http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf

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

What happens when meiosis goes wrong?  NONDISJUNCTION!!!

Meiosis Animations Frame-by-frame animation http://www.csuchico.edu/~jbell/Biol207/animations/meiosis.html