Sci 9A Lesson 5 April 7 - Meiosis
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Transcript of Sci 9A Lesson 5 April 7 - Meiosis
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Homework from last class:• Complete the Introduction to Meiosis and
Reproductive Systems worksheet
• Study for your Genetics and Reproductive Systems quiz
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Quiz Time!
You have about 10 minutes to write the quiz.
Good luck!
2
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Chapter 6 pp. 191-197
Ch. 6.1 Meiosis
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MeiosisMeiosis: the form of cell division that produces
gametes (sex cells) with half the number of chromosomes as body cells
Diploid (2n) Haploid (n) parent cell sex cells
Meiosis only occurs in gonads (testes or ovaries)
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Meiosis is similar to mitosis, but there are several differences:• Involves 2 cell divisions•Results in 4 cells with ½ the genetic information (n instead of 2n)
Meiosis occurs in 2 phases:
Meiosis I (1st cell division)
Meiosis II (2nd cell division)
Meiosis I
Meiosis II
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Meiosis I• Prior to meiosis I, DNA replicates once, in
interphase
Fig 6.4 p. 191
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Meiosis I• In meiosis I, a pair of matching homologous
chromosomes, one from each parent, lines up at the equator
Homologous chromosomes: a pair of matching chromosomes
Fig 6.5 p. 191
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Meiosis I• Homologous
chromosomes line up at the equator
• The homologous chromosome pair separates and moves to opposite poles of the cell
• 2 daughter cells result
Fig 6.5 p. 191
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Crossing Over
Crossing over: event in meiosis I where non-sister chromatids exchange segments of DNA; results in variation in gametes
• As a result of crossing over, each chromosome picks up new genetic information from the other
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Independent Assortment
Independent assortment: an event in meiosis I where homologous pairs of chromosomes separate and sort themselves into daughter cells
• Genes are shuffled leads to genetic diversity
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Crossing Over and Independent Assortment
Fig 6.6A p. 192
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Meiosis II
• DNA not replicated again before meiosis II begins
• Meiosis II is like mitosis the chromatids of each chromosome are pulled to opposite poles
• Each daughter cell inherits 1 chromatid from each chromosome
• 4 haploid (n) daughter cells result
Fig 6.4 p. 191
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Outcome of Meiosis II Fig 6.6B p. 193
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Summary of Meiosis
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Meiosis Animationhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/
animation__how_meiosis_works.html
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Homework for next class:
It was fun teaching you during my
practicum! Best of luck to you
all!
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Works CitedImages taken from the following sources:http://biologydiva.pbworks.com/w/page/14796955/Chapter-22http://chsweb.lr.k12.nj.us/mstanley/outlines/meiosis/APMeiosis.htmhttp://www.bcscience.com/bc9/index.htmlhttp://geneticssuite.net/node/21http://www.sflorg.com/sciencenews/scn100608_01.html