Meiosis

MeiosisWhy Do cells Go through Meiosis?Cells go through Meiosis in order to make Sex CellsSex cells are also called GametesFour Daughter Cells are createdHaploid (1N)

InterphaseCell GrowsDuplicates DNACell Prepares to divide

After InterphaseIn order to make sex cells or cells with half the number of chromosomes meiosis has TWO phases

Meiosis I and Meiosis IIProphase IChromosomes Condense (become visible)Homologous chromosomes form a tetrad (4 chromatids)- paring up called SYNAPSISCrossing Over Occurs!

Crossing OverHomologous Chromosomes- Similar chromosomes and genes in the same location, but come from different parentsWhen the chromosomes touch they switch genetic information CROSSOVERCauses genetic variation in the resulting gametes

Knowledge CheckWhy do cells go through meiosis?A- to replicate body cellsB- To replicate sex cells

Whats the name of the type of cell formed through meiosis?A- gametesB- somatic cells

What important event leads to genetic variation?A- homologous chromosomesB- TetradC-Crossover

Crossover close-up with results

Metaphase I Homologous chromosomes move together to the middle of the cellSpindle attaches to the centromere

Anaphase IHomologous chromosomes separateSister chromatids stay attachedMove towards opposite poles

Telophase IDivision of cytoplasmCreates Two daughter cellsBegin Meiosis IIThere is a brief interphase, but no DNA replicationWhy?Knowledge CheckDuring Anaphase I in meiosis:A- The sister chromatids separate to opposite polesB- The homologous chromosomes separate to opposite poles

Name the stage

Prophase IISpindles re-appearNuclear membrane stays separated

Metaphase IIChromosomes line up in the middleSpindle attaches

How are metaphase I and II different?

Anaphase IISister Chromatids Separate from each other

How are Anaphase I and II different from eachother?

Telophase IINucleus reformsDivision into four daughter cellsHaploid (1N)Gametes (egg and sperm)

Knowledge Check- Name the phase

Final Results of Meiosis4 haploid daughter cells which will develop into sex cellsEach daughter cell has half of the genetic information of a somatic cell23 chromosomes for each sex cellNOTE:Males will create 4 sperm cells for every one cell that goes through meiosisFemales will create 4 egg cells, BUT 3 will turn into non usable polar bodies and 1 will mature into an egg cell.

Lets watch Meiosis in Motionhttp://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit3/bio_ch06_0175_ab_meiosis.htmlhttp://www.sumanasinc.com/webcontent/animations/content/meiosis.html

Through sexual reproduction and fertilization, these gametes fuse to form one diploid cell again (2n 46 chromosomes).

Zygote= a fertilized egg

Zygote will begin to rapidly mitotically divide to make more cells to form a BLASTOCYST and then develop into an EMBRYO.

Fertilization and Lifehttp://glencoe.mcgraw-hill.com/sites/dl/free/0078617022/161752/00053403.html

Clay meiosisAs a class we will use the clay, yarn, and string to go through the phases of meiosis so that you can visually see what happensCreate Prophase 1 with your clay and yarn- SHOW CROSSOVER

Create metaphase 1 with your clay and yarn

Create anaphase 1 with your clay and yarn

Create Telophase 1 with your clay

Move the chromosomes in position for prophase and metaphase 2- NOTICE EACH CHROMOSOME IS DIFFERENT

Position the chromosomes, spindle fibers, and centrioles to anaphase II

Position your chromosomes for telophase and cytokinesis

Things to notice about the results4 resulting daughter cells. Contains only 1 set of genetic information in the chromosome haploidnEach daughter cell contains chromosomes that are genetically different from one anotherThese daughter cells will develop into full sex cells (gametes). Sperm for males and egg for female