Meiosis Animation. Meiosis A second type of cell division designed to make haploid cells called gametes Gametes include sperm and egg Meiosis occurs in

Meiosis Animation

Kathy Da Silva, Centre High, 425 6753

MeiosisA second type of cell division designed to make haploid cells called gametesGametes include sperm and eggMeiosis occurs in 2 parts Meiosis 1 and Meiosis 2Meiosis 1 is a reductive division where homologous chromosomes line up together on a spindle fiberTherefore, # spindle fibers required = half of diploid number = haploid numberMeiosis Tutorial: The Biology Project!


Structure formed when chromosomes come together is called a tetradA tetrad consists of 2 replicated chromosomes or 4 chromatidsChromatids are chromosomes that are still attached to their sister strand via a centromereWhen centromere eventually splits and chromatids are free of their sister chromatid, both are called chromosomes.this does not happen until anaphase 2Excellent Narrated Movie of Meiosis


Main Difference between Mitosis and MeiosisDuring prophase 1, homologous (similar) chromosomes come together This process is known as synapsisDuring this time the chromosomes are so close together that crossing over can occurThis leads to genetic variation since sections of the DNA are exchanged mixing maternal and paternal genes


Prophase 1Nuclear membrane disintegratesSpindle fibers formChromosomes become distinctHomologous (similar) chromosomes come together This process is called synapsis


Stages of MeiosisAlways ask yourselfWhats going on here?


Stages of Meiosis


Metaphase 1Homologous replicated chromosomes line up on the same spindle fiberIndividual chromatids in the replicated chromosomes do not separate yetNot until Anaphase 2In human cell, since 2n = 4623 pairs line upTherefore 23 spindle fibers are neededIf 2n = 10, 5 spindle fibers are required for this stage


Stages of Meiosis


Anaphase 1Homologous replicated chromosomes separate to opposite polesCentromeres do not split yet


Stages of Meiosis


Telophase 1Chromosomes arrive at opposite polesCytoplasm pinches inCytokinesis occurs in animal cellsEquatorial plate forms in plant cells2 haploid cells formChromosomes may become chromatin and enter an interphase 2 in some cells


Stages of Meiosis


Prophase 2New spindle fibers formNuclear membrane dissolvesChromosomes become visibleIf 2n = 10, then only five spindle fibers neededwhy?Half of the chromosomes are in the other cell


Stages of Meiosis


Metaphase 2Chromosome line up on new spindle fibersChromosomes here are made up of 2 chromatidsIf 2n = 46, 23 chromosomes are in each cell produced from telophase 1This means that 23 spindle fibers must be presentIf 2n = 8, 4 spindle fibers needed now


Stages of Meiosis


Anaphase 2Centromere splitsChromatids (now called chromosomes) migrate to opposite poles of the cell


Stages of Meiosis


Telophase 2Chromatids (now called chromosomes) arrive at polesCytoplasm starts to pinch in Cytokinesis occursEnd result is 4 haploid cells2 from each of the 2 cells produced at the end of telophase 1


Stages of Meiosis


Notice the difference


Stages of MeiosisEnd result of


Overview of Meiosis 1


Overview of Meiosis II


Meiosis in males and femalesIn males called SpermatogenesisInvolves production of 4 equal sized cells each with same amount of cytoplasmic organellesIn females called OogenesisFirst division unequal One cell is a polar body and smallerSecond division produces another smaller cell called a polar body and then the EggEgg contains the majority of cytoplasmic organelles


Oogenesis


Spermatogenesis


Meiosis Produces Sperm Cells


Structure of Human Sperm


Abnormal MeiosisWhen homologous chromosomes fail to separate during anaphase of meiosisAbnormal gametes form with abnormal numbers of chromosomes (trisomy 21 etc..)Process called non-disjunctionKaryotyping used to detect disordersChromosomes are arranged according to 3 characteristicsCentromere position Banding pattern SizeNon-disjunction animation


Sources of Variation1. Gamete success2. Crossing overdepends on distance between genes andlength of chromosome3. Independent Assortmentthe way one homologous pair lines up has nothing to do with the way another homologous pair lines up!


Animation of Crossing OverAnother great animation!!


Homologous pair of chromosomes


Independent Assortment


Detecting genetic DisordersUltrasound locates position of fetusAmniocentesis uses a needle to withdraw some amniotic fluid from around fetusFluid is in uterusFetal cells can be analysedChorionic Villus Sampling (CVS) draws cells from outer membrane of embryoCVS can be used as early as 8 weeks of pregnancy


Animal Life Cycle


Plant Life CycleAlternation of GenerationsSexual Stage Alternates with Asexual


Plant and Animal Life Cycle


Spermato-genesisOogenesisSpermEgg (Ovum)ZygoteEmbryoFetusChildMeiosisMitosis


MossLife CycleDemonstratesAlternation Of Generations


Alternation of GenerationsMoss PlantSexual stage alternates with an asexual stageSexual stage involves fertilization by union of 2 gametes (needs water)Asexual stage involves spore productionOne cannot exist without the otherMitosis & Meiosis occursSexual & Asexual stage separateFern PlantSame

Same

Same

Same

Sexual & Asexual stage on same plant


Fern Life CycleAlternation of generations


Alternation of Generations in Fern Plants


Cell Division Tutorials/Questions


Documents

Meiosis Animation. Meiosis A second type of cell division designed to make haploid cells called gametes Gametes include sperm and egg Meiosis occurs in