ib biology 10 genetics hl 10.1 meiosis shelly fargo jason de nys all syllabus statements ©ibo 2007...
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IB Biology10 Genetics HL
10.1 Meiosis
Shelly FargoJason de Nys
All syllabus statements ©IBO 2007All images CC or public domain or link to original material.
http://www.flickr.com/photos/carolinabio/6241450806/
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10.1.1 Describe the behaviour of the chromosomes in the phases of meiosis
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The best way to see what happens in this dynamic process is to view some
animationsThere is a link to 3 Videos on PowerPoint 4.1!!!
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We made a summary of notes in class that is similar
(ours is more indepth) to slide 2. You should practice drawing this on your own.
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10.1.2 Outline the formation of chiasmata in the process of crossing over
Hmmmm… chiasmata,chiasmata,
chiasmata…
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10.1.2 Outline the formation of chiasmata in the process of crossing over
Hmmmm… chiasmata,chiasmata,
chiasmata…
Singular: chiasma….You may have hear this word before in another context
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http://en.wikipedia.org/wiki/File:Gray773.png
Ah yes!The place where some of the optic nerves cross over in the brain
Greek khīasma, cross-piece, from khīazein, to mark with an X, from khei, khī, chi (from the letter's shape). http://www.wordnik.com/words/chiasma
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Crossing over involves the swapping of segments of DNA between chromatids on homologous pairs
The points at which the chromatids cross are the
chiasmata
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© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed. (Sunderland, MA: Sinauer Associates and W. H. Freeman & Company), 198. Used with permission. All rights reserved
Chiasmata: evidence of exchange between chromatidsThis micrograph shows a pair of homologous chromosomes, each with two chromatids, during prophase I of meiosis in a salamander.
Two chiasmata are visible.
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10.1.3 Explain how meiosis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphase I
• Crossing over can occur on any part of a chromosome.
• The size of the section swapped between chromosomes can be almost any size.
• The number of chiasmata on each chromatid can vary
These three points alone lead to innumerable possibilities
You viewed this animation in PowerPoint 4.1
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From the animation on the previous page:
Number of possible orientations =
Work it out for the human genome! (Hint…we did this in class on our meiosis drawing)
One of the strange results you get when you Google
“random orientation”
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Number of possible orientations =
Work it out for the human genome!
possibilities!
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10.1.4 State Mendel’s Law of independent assortment.
http://www.flickr.com/photos/staipale/2580650017/http://commons.wikimedia.org/wiki/File:Gregor_Mendel.png
Each pair of alleles segregates into gametes independently
Also… mmm…
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http://commons.wikimedia.org/wiki/File:Independent_assortment_%26_segregation-it.svg
An example of the independent assortment of the gene for
colour (green [y] or yellow [Y]) and the gene for pod type
(smooth [R] or wrinkled [r])
In Italian for your pleasure!
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10.1.5 Explain the relationship between Mendel’s law of independent assortment and meiosis
http://www.flickr.com/photos/kaptainkobold/356759039/
Mendel examining his pea flowers
My babies…
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Mendel knew nothing of modern genetics, genes had not been discovered. He was working from the traits he observed, the phenotypes. He named the heritable factors alleles.
So his Law:Each pair of alleles segregates into gametes independently.
…relates to the random orientation of homologous chromosomes during meiosis in metaphase I
http://commons.wikimedia.org/wiki/File:MetaphaseIF.jpg
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How do I answer that one for the IB Bio Test?
• The Law of Independent assortment states that each pair of chromosomes orientate themselves on the metaphase plate independently of other pairs of chromosomes during meiosis (metaphase I). – Don’t know which side of the metaphase plate the ‘mom’ chromosomes
and the ‘dad’ chromosome will be on• In meiosis I homologous chromosomes arranged randomly at the
equatorial plate during metaphase I• In meiosis I homologous pairs of chromosomes segregate to
opposite poles of the cell during anaphase I (Law of segregation)• This is necessary for independent assortment of genes and
therefore alleles.
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Further information:
Three of the best sites for IB-specific Biology information. The top link takes you to the PPT by Stephen Taylor
^ Excellent article available on Scitable
Doo do do do do ,do doo do do do do, do do do