Meiosisformoodle2013 14-140122101626-phpapp02
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Transcript of Meiosisformoodle2013 14-140122101626-phpapp02
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Organisms receive half of their DNA from each parent
Sperm and eggs cells (haploid) combine to create a zygote (diploid)
Used by most animals, fungi, plants, and algae
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Haploid gametes (n = 23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Ovary Testis
Diploidzygote(2n = 46)
2n
MitosisKey
Haploid stage (n)Diploid stage (2n)
Multicellular diploidadults (2n = 46)
A life cycle
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Humans body cells are diploid (2N) 2N = 46
Gametes - sex cells Males – sperm Females – eggs
Gametes are HAPLOID N = 23
Fertilization restores the diploid state
(N + N = 2N) Zygote - a fertilized
egg (2N)
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What happens during Interphase???DNA REPLICATION!!!
2N
2N
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Occurs in Prophase I Chromosomes exchange portions of their
chromatids Increases genetic variation
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© 2012 Pearson Education, Inc.
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Homologous chromosome pair
© 2012 Pearson Education, Inc.
Centromere
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• Prophase I – homologous chromosomes form tetrads & crossing over occurs• Metaphase I – tetrads line up along the middle
• Anaphase I – homologous chromosomes separate
• Telophase I – two nuclei form
• Cytokinesis I – cells separate
2N
N N
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• Prophase II – spindle forms, prepares for division
• DNA replication DOES NOT occur between Meiosis I & II
• Metaphase II – chromosomes align along the center
• Anaphase II – sister chromatids separate
• Telophase II – nuclei reform; cytokinesis
N N
N
N NN
Looks A LOT like MITOSIS!
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Prophase II Metaphase II Anaphase II
Haploid daughtercells forming
Telophase IIand Cytokinesis
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3
SUMMERY OF THE MEIOSIS PROCESS
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Process to make haploid gametes
Chromosome # is cut in half
2N N Occurs in ovaries & testes TWO cell divisions Increases genetic variation
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Down syndrome
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Down syndrome
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Men: 4 sperm are made
Women: only 1 egg is made
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© 2012 Pearson Education, Inc.
Deletion
Duplication
Inversion
Reciprocal translocation
Homologouschromosomes Nonhomologous
chromosomes
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Meiosisvs.Mitosis
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In meiosis, “crossing over” occurs during metaphase I.
Chromosomes form tetrads
Homologous chromosomes “swap” parts of their DNA leads to genetic variation
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Mitosis makes cells for growth, development, repair, and asexual reproduction
Meiosis makes cells for sexual reproduction
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The following table lists the most common human sex chromosome abnormalities.
© 2012 Pearson Education, Inc.
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Campbell &Reece,(2010) Biology Williamson, J. LS3AFET . Unit 3. University of
Johannesburg: Science Department, 2014. Shilma, S. Meiosis. (2011). http://www.worldstarhiphop.com/videos/vi
deo.php?v=wshhk0A758v5lEkmCKrk