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