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/

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

animationsThere is a link to 3 Videos on PowerPoint 4.1!!!

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.

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….You may have hear this word before in another context

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

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

You viewed this animation in PowerPoint 4.1

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”

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 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

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.

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