topic 4.2 & 10.1 notes
DESCRIPTION
Topic 4.2 & 10.1 Notes. Meiosis. A reduction in chromosomes to form HAPLOID cells. 2N to 1N. Homologous pairs . They associate with each other during prophase 1 through synapsis. Chromosomes replicate in which phase?. S phase!. Prophase 1. - PowerPoint PPT PresentationTRANSCRIPT
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Topic 4.2 & 10.1 Notes
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Meiosis• A reduction in
chromosomes to form HAPLOID cells.
• 2N to 1N
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Homologous pairs • They associate with each other during prophase 1
through synapsis.
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Chromosomes replicate in which phase?
• S phase!
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Prophase 1• The homologous chromosomes form BIVALENTS.
These are replicated homologous chromosomes.• The sister chromatids are next to each other,
joined at the centromere.
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Crossing Over• Non sister chromatids may cross over during
prophase 1 leading to recombinant alleles.
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More detail on Prophase 1
Synapsis-the chromosomes associateCrossing Over-The Chiasma are the points at which they cross over. A Holliday junction forms when they anneal.This increases genetic diversity!
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Metaphase 1• Bivalents line up at
the equator double file.
• There are many positions that they can align themselves in.
• This adds to the genetic variation…more on this later!
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Anaphase 1• This is where the reduction takes place. The pairs
separate, but the sister chromatids remain attached!
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Non Disjunction
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Telophase 1• The cells are no longer diploid here.• The chromosomes may not be exact matches of
each other due to crossing over.
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Cytokinesis 1
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Prophase II• The nuclei break down again, but the
chromosomes do not cross over again.
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Metaphase II• Random orientation again contributes to variation
in gametes.
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Anaphase II• Chromatids are pulled to the opposite poles.
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Telophase II and Cytokinesis
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Oogenesis
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Spermatogenesis
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Mendel and Independent Assortment
• The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.
• This is only true for unlinked genes.• Click here for a more detailed explanation.
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HOMEWORK 4.2/10.1• Make a T Chart to compare/contrast
mitosis and meiosis.• Please include as many as possible,
but a minimum of 6.• You may need to do some research
ON YOUR OWN.• Due Friday