meiosis what is it? what is it? making of gametes making of gametes sex cells sex cells sperm...
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MEIOSISMEIOSIS
What is it?What is it? Making of gametesMaking of gametes
Sex CellsSex Cells Sperm (pollen) in malesSperm (pollen) in males Eggs (ova) in femalesEggs (ova) in females
Diploid Diploid Haploid Haploid Involves:Involves:
Cell divisionCell division 2 nuclear divisions2 nuclear divisions
Reduction of chromosome number by halfReduction of chromosome number by half
The human life cycleThe human life cycle
Egg cell
Sperm cellFERTILIZATIONMEIOSIS
Mitosis anddevelopment
Diploidzygote (2n = 46)
Multicellulardiploid adults (2n = 46)
Haploid gametes (n = 23)
Chromosomes
Centromere
Sister chromatids
•Somatic cells of each species contain a specific number of chromosomes
•Human cells have 46, making up 23 pairs of homologous chromosomes
•In each homologous pair - ~ 1 comes from “Mom” ~ 1 comes from “Dad”
Homologous Chromosomes
InterphaseInterphase
Just like “Interphase” of MitosisJust like “Interphase” of Mitosis GG1 1 ~ ‘Gap’ 1 = growth and preparation~ ‘Gap’ 1 = growth and preparation
S ~ ‘Synthesis’ = DNA replication to makeS ~ ‘Synthesis’ = DNA replication to make
exact copies of the chromosomesexact copies of the chromosomes
GG22 ~ ‘Gap’ 2 = growth and shape change ~ ‘Gap’ 2 = growth and shape change
Meiosis I ~ Reduction Meiosis I ~ Reduction DivisionDivision
Prophase IProphase I Chromatin thickens into chromosomesChromatin thickens into chromosomes
You can now see them under a light microscopeYou can now see them under a light microscope Nuclear membrane begins to disintegrateNuclear membrane begins to disintegrate Centrioles migrate to opposite polesCentrioles migrate to opposite poles Homologues do something unique to meiosisHomologues do something unique to meiosis
Prophase I - continuedProphase I - continued
Homologous Pairs line up next to each otherHomologous Pairs line up next to each other SynapsisSynapsis forms a tetradforms a tetrad
Crossing OverCrossing Over pieces of the chromosomes ‘switch’ placespieces of the chromosomes ‘switch’ places
Stay connected at Stay connected at Chiasma(ta)Chiasma(ta)
MOST IMPORTANT ~MOST IMPORTANT ~ for genetic diversity for genetic diversity
Metaphase IMetaphase I Attached homologues line up on metaphase Attached homologues line up on metaphase
plateplate Anaphase IAnaphase I
Tetrads separate at chiasma(ta)Tetrads separate at chiasma(ta) ** sister chromatids are STILL together** sister chromatids are STILL together
Telophase ITelophase I Homologues move to polesHomologues move to poles 2 nuclear membranes form (in some cells)2 nuclear membranes form (in some cells)
** Chromosome number is now ** Chromosome number is now HAPLOIDHAPLOID
~~ there is now half the number of original there is now half the number of original chromosomeschromosomes
from the parent.from the parent.
InterkinesisInterkinesis
Stage between Meiosis I and IIStage between Meiosis I and II Resting stageResting stage NOT another InterphaseNOT another Interphase
NO DNA replication NO DNA replication Strictly a “recovery” phase orStrictly a “recovery” phase or
rest period before moving on.rest period before moving on.
Meiosis II – like MitosisMeiosis II – like Mitosis Prophase IIProphase II
Just like Meiosis I – but NO crossing overJust like Meiosis I – but NO crossing over Metaphase IIMetaphase II
Sister chromatids line up on metaphase Sister chromatids line up on metaphase plateplate
Usually at right angles to meiosis IUsually at right angles to meiosis I Anaphase IIAnaphase II
Sister chromatids separate at centromere Sister chromatids separate at centromere andand
move to opposite polesmove to opposite poles Telophase II and CytokinesisTelophase II and Cytokinesis
4 new nuclei are formed 4 new nuclei are formed Each are haploidEach are haploid
Crossing Over = Genetic Diversity
Mitosis and Meiosis Compared
WEB LINKSWEB LINKS
http://www.lewport.wnyric.org/jwanamahttp://www.lewport.wnyric.org/jwanamaker/animations/meiosis.htmlker/animations/meiosis.html
http://www3.telus.net/byngscience/sc1http://www3.telus.net/byngscience/sc10/Sc10~Biology/s_tan_division.swf0/Sc10~Biology/s_tan_division.swf
http://www.pbs.org/wgbh/nova/baby/dihttp://www.pbs.org/wgbh/nova/baby/divi_flash.htmlvi_flash.html