Eduard

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Meiosis Mitosis
Walther Flemming
Eduard Strasburger
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I.
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Animation 3.2
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Animation 3.3
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II.
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START A / a
Genes exist, come in pairs
Gametes only 1 gene copy
pair of copies SEGREGATE
Each gamete only 1 gene copy
alleles combine randomly In offspring
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a / a
Gametes only 1 gene copy
Genes exist, come in pairs
pair of copies SEGREGATE
What about second law?
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Animation 5.1a
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Mendels 2nd Law Genes segregate
independently ??? ???? ??? ???? ???????? (?????)

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Parental
Recombinant Parental Recombinant Parental
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If we have a third gene for seed size
biggtsmall B/b, and TRI-hybrids
R/r Y/y
¾ of these seeds will be big ¼ of these
seeds will be small ¾ of these seeds
will be big ¼ of these seeds will be
small ¾ of these seeds will be big ¼ of
these seeds will be small ¾ of these seeds
will be big ¼ of these seeds will be
small
27/64 9/64 9/64 3/64 9/64 3/64 3/64 1/64
64/64
9 3 3 1
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If we look at the GENOTYPE ratios - With a
second gene for seed texture round/wrinkled
1/4 of these seeds will be RR 2/4 of these seeds
will be Rr 1/4 of these seeds will be rr 1/4 of
these seeds will be RR 2/4 of these seeds will be
Rr 1/4 of these seeds will be rr 1/4 of these
seeds will be RR 2/4 of these seeds will be
Rr 1/4 of these seeds will be rr
1/16 2/16 1/16 2/16 4/16 2/16 1/16 2/16 1/16 16/
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YY Yy yy
Genotype ratios 121242121 Phenotype
ratios 9331
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• Mendels rules are relevant for organisms that
  sexually reproduce diploid/haploid
• Plants, Animals, many Monera

Those that do meiosis
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III-IV
Sex chromosomes The breakthrough to the
chromosomal theory of inheritance
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Nettie Stevens
Thomas H. Morgan
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Animation 3.3
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Thomas H. Morgan
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Reciprocal
White Red Mothers Fathers
Red White Daughters Sons
Board
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?? ??
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????????
F6 F7
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????? ??????? ?? ?????
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To be a male Fly ratio of X
chromosomes to autosomes 1 Man
Presence of Y chromosome
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Barr body
For dosage compensation, 1 X chromosome is
condensed, silenced in females
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Y linked trait??
Y?
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First Second
(reciprocal)
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Mammals Fruitflies
Moths
Homogametic Heterogametic
Heterogametic
Homogametic
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