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Bio Prezis SPSCepiel

on 17 February 2013

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Transcript of Meiosis

Cell Division that leads to gametes. Meiosis Remember those chromosomes we talked about in mitosis? See if you can define them before you move on in the Prezi. Chromosomes Part 2 Humans have 2 sets of chromosomes -- one from mom and one from dad. More about Chromosomes Cells with a single set of chromosomes.
For humans, haploid cells have 23 chromosomes. They are abbreviated n. Haploid Cells MEIOSIS! How do we make haploid cells
(egg and sperm)? Interphase: Chromosomes duplicate but are not visible yet. Stages of Meiosis The top images are what you would see under a microscope. Do the look familiar? Meiosis 1 Anatomy of a chromosome: Homologous chromosomes: 2 chromosomes
that carry the genes for the same
inherited traits. Diploid Cells (2n): any cell with 2 homologous sets of chromosomes. For humans, the 2n = 46, meaning we have 46 chromosomes in each cell. What cells are haploid in the
human body? EGG & SPERM Try to figure out why this
makes sense. Why would
egg and sperm have half the
chromosomes of the normal
body cells? Meiosis is a special cell division that reduces the chromosome number from diploid to haploid (2n to n). From 46 to 23 in humans. Watch the overall process of meiosis with Mr. Andersen and then we will look at the stages more slowly in the Prezi. Meiosis II Refer to pages 136
to 144 for this Prezi. How do the numbers work out for human chromosomes? What does meiosis have to do with
genetic variation?
(we discussed this during evolution -- do you remember?) 1. Independent assortment 2. Crossing over Independent Assortment The manner in which the chromosome pairs line up during Metaphase 1 determines which chromosomes end up in each gamete. Watch the following animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__random_orientation_of_chromosomes_during_meiosis.html Use your calculator to figure out how many different possible chromosome combinations exist for each gamete you produce. 8 million combos!!!! 3. Random fertilization Crossing Over Random Fertilization The sperm and egg that come together do so randomly. If you factor in the independent assortment and random fertilization, there are 64 trillion possible combinations of chromosomes! the end It increases variation -- this is why we
are all different from each other. 3 mechanisms that cause this variation:
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