ib biology ahl 10.1: meiosis
DESCRIPTION
A slideshow for students and teachers of IB HL BiologyTRANSCRIPT
IB Biology10 Genetics HL
10.1 Meiosis
Jason de Nys
All syllabus statements ©IBO 2007All images CC or public domain or link to original material.
http://www.flickr.com/photos/carolinabio/6241450806/
10.1.1 Describe the behaviour of the chromosomes in the phases of meiosis
The best way to see what happens
in this dynamic process is to view some animations
67% of the animations on this page are voiced by men with deep voices. Therefore, they must
be authoritative.
Make your own summary notes of what goes on
during meiosis, refer to the animations as necessary
10.1.2 Outline the formation of chiasmata in the process of crossing over
Hmmmm… chiasmata,chiasmata,
chiasmata…
10.1.2 Outline the formation of chiasmata in the process of crossing over
Hmmmm… chiasmata,chiasmata,
chiasmata…
Singular: chiasma….where have I heard that before?
http://en.wikipedia.org/wiki/File:Gray773.png
Ah yes!The place where some of the optic nerves cross over in the brain (Option E: E2.5 maybe you haven’t done it yet,
or you might do a different option)
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
Crossing over involves the swapping of segments of DNA between chromatids on homologous pairs
The points at which the chromatids cross are the
chiasmata
© 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.
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
View the animation to answer the question on the next slide
From the animation on the previous page:
Number of possible orientations =
Work it out for the human genome!
One of the strange results you get when you Google
“random orientation”
Number of possible orientations =
Work it out for the human genome!
possibilities!
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…
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!
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…
Mendel new 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
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