BIO201A Cell Biology Lecture 37 Monday 04/23/07
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Transcript of BIO201A Cell Biology Lecture 37 Monday 04/23/07
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BIO201A Cell Biology
Lecture 37
Monday 04/23/07
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Important Announcements:
– Friday, April 27, will be a review of the lab material.– Monday, April 30, will be the last day of classes and will
be carried out as a recitation. No new material will be presented. If you have questions about the lecture material, that is the time to ask about it.
– Next exam will be the Final. 34 questions over section 3 and 14 lab questions. This is 48 total questions worth 140 total points.
– Final exam is May 8th, 11:45AM to 2PM in four rooms:
NSC 201 (lab sections A1-A4)NSC 218 (lab sections A5-A8) Norton 112 (lab sections A9-A12)OBrian 109 (lab sections A13-A16). Please note which room you will need to attend.
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Aneuploidy
1. Autosomal polyploidy. This is usually fatal except in the case of trisomy 21 (three chromosome #21)
2. Autosomal monosomy. Only one of the autosomes instead of two. This is usually fatal
1. Sex chromosome polyploidy.
XXY is male with Kleinfelter’s syndrome
XYY is male and was previously thought to have criminal tendencies because of being “too male”
4. Sex chromosome monosomy.XO is female with Turner syndrome
All of these are caused by nondisjunctions during meiosis
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Aneuploidy in a cancer cell
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Cross-over recombination and chiasmata
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Two sources of genetic variability in Meiosis:
1. Crossing over and recombination.
This happens in pacytene of prophase I
1. Independent Assortment of genetic traits (maternal and paternal)
This happens in Anaphase I of meiosis
It produces genetic diversity
What does this do?
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20_07_recombination.jpg
Crossing-over and recombination occurs
between non-sister chromatids in pachytene
Recombination
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Chiasmata in Diplotene phase of meiotic prophase I
chiasmata
Chiasmata are covalent linkages between two non-sister chromatids. This helps to keep bivalents together after cohesion
linkages are broken
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20_08_Chiasmata.jpgSegregation of chromatids modified by recombination
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20_09_kinetochore_pull.jpgThe chromatids of each gamete are different in this case
The DNA sequences of each chromatid is different. Each gamete can get different genetic information.
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20_11_reassortment.jpgIndependent Assortment Recombination
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Different strategies for mitosis and meiosis
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Gametic or terminal
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Fungi. Zygotic or initial
1n 1n
2n
1n 1n
Fertilization
Meiosis
Plants, Sporic or intermediate
+Pollen (1n)
Egg (1n) 2n zygote
fertilization
mitosis
2nsporophyte
1n 1n
meiosis
Spores (haploid gametophytes)
Haploid
Mitosis
Haploid adults
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Primary spermatocytes (2n4x4c)
Meiosis I
Secondary spermatocyte (1n2x2c)
Spermatids (1n1x1c)
Meiosis II
Sperm cells (1n1x1c)
Differentiation
Primary oocyte (2n4x4c)
Secondary oocyte (1n2x2c)
Differentiation
Meiosis I
THEN
Polar body (1n1x1c)
Egg (1n1x1c)
Meiosis II
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Summary Mitosis produces daughter cells with the same genotype as
the mother cell
No genetic segregation or independent assortment in mitosis
Meiosis produces cells with different mixtures of maternal and paternal genes because of:
Independent assortmentGenetic recombination
Independent assortment and recombination happen in meiosis, not mitosis
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Cloning animals nextFrom genetic variation to genetic uniformity