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Meiosis & Sexual Reproduction
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Cell division / Asexual reproduction
Mitosis ______________________________ identical daughter cells clones same genetic information Aaaargh! I’m seeing double!
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Asexual reproduction Single-celled eukaryotes
yeast Paramecium Amoeba Simple multicellular eukaryotes Hydra budding What are the disadvantages of asexual reproduction? What are the advantages?
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+ 46 46 92 How about the rest of us?
What if a complex multicellular organism (like us) wants to reproduce? joining of egg + sperm Do we make egg & sperm by mitosis? No! What if we did, then…. 46 + 46 92 egg sperm zygote Doesn’t work!
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Human female __________
_______________ 2n Human female __________ ___________________ ___
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_______________ 2n Human female __________ ___________________ ___
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How do we make sperm & eggs?
Must reduce 46 chromosomes 23 must _______ the number of chromosomes __________ 23 46 _________ 23 46 egg 23 _________ 46 23 _____________ sperm __________
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Meiosis makes sperm & eggs
46 chromosomes to 23 chromosomes half the number of chromosomes 23 46 egg __________ 46 23 __________ __________ sperm
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homologous chromosomes double stranded homologous chromosomes
Paired chromosomes Homologous chromosomes both chromosomes of a pair carry “matching” genes control same inherited characters homologous = same information diploid 2n 2n = 4 eye color (brown?) eye color (blue?) homologous chromosomes double stranded homologous chromosomes
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Meiosis 1 overview 1st division of meiosis double stranded
Divide 1 Copy DNA Line Up 1 prophase 1 metaphase 1 _____________ telophase 1 _____________ _________
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4 Meiosis 2 overview 2nd division of meiosis _________
Bye Bye 2 Meiosis 2 overview telophase 1 Line Up 2 4 2nd division of meiosis looks like mitosis metaphase 2 _____________ _________
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Meiosis = reduction division
special cell division in sexually reproducing organisms _____________________________ ___________________ makes ______________ sperm, eggs
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Meiosis & mitosis __________________________ ____________
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Sexual reproduction lifecycle
2 copies diploid 2n 1 copy haploid 1n 1 copy haploid 1n _____________ _____________ We’re mixing things up here! A good thing?
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Putting it all together…
meiosis fertilization mitosis + development gametes 46 23 46 23 46 46 46 46 46 23 meiosis 46 46 egg 46 46 23 zygote fertilization mitosis & development mitosis sperm
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The value of meiosis 1 _____________________
________________________________________________________________________ Mom from Mom Consider the greater variation with 23 pairs of chromosomes = mixing and matching Dad offspring from Dad
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new gametes made by offspring
We’re mixing things up here! The value of meiosis 2 __________________________ _______________________________ gametes of offspring do not have same genes as gametes from parents new combinations of traits Consider the greater variation with 23 pairs of chromosomes = mixing and matching from Dad variation from Mom offspring new gametes made by offspring
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How does this explain: family resemblance & differences!
Why are the kids so similar to the parents but not exact? Michael & Kirk Douglas Baldwin brothers Martin & Charlie Sheen, Emilio Estevez
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Any Questions?? What are the advantages of asexual reproduction?
What are the DISadvantages of asexual reproduction? Any Questions?? What are the advantages of sexual reproduction? What are the DISadvantages of sexual reproduction?
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