1. IB Biology 10 Genetics HL 10.1 Meiosis Shelly Fargo Jason de Nys All syllabus statements ©IBO 2007 All images CC or public domain or link to original material. http://www.flickr.com/photos/carolinabio/6241450806/

2. 10.1.1 Describe the behaviour of the chromosomes in the phases of meiosis

3. The best way to see what happens in this dynamic process is to view some animations There is a link to 3 Videos on PowerPoint 4.1!!!

4. 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.

5. 10.1.2 Outline the formation of chiasmata in the process of crossing over Hmmmm… chiasmata, chiasmata, chiasmata…

6. 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

7. 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 http://www.wordnik.com/words/chiasma

8. Crossing over involves the swapping of segments of DNA between chromatids on homologous pairs The points at which the chromatids cross are the chiasmata

9. © 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 reservedSinauer Associates Chiasmata: evidence of exchange between chromatids This micrograph shows a pair of homologous chromosomes, each with two chromatids, during prophase I of meiosis in a salamander. Two chiasmata are visible.

10. 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

11. One of the strange results you get when you Google “random orientation”

13. 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…

14. 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!

15. 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… My babies…

16. 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

17. 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.

18. 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