If you're reading on, then you're right in the middle of reading the Lecture 5 Blog and you followed the proper link. Congratulations, either I haven't bored you to death or you'll do just about anything to do well on Exam 1! In that case...the text below is a short diversion from the Lecture 5 Blog designed especially for you...
You have been told in that post, and also in a previous post ("Learning the Language of Variation") that meiosis and variation have some intimate connections. Given all the time I've put into the Lecture 5 Blog today, I can't afford to go in much detail about meiosis and variation above and beyond what I've already included in the aforementioned posts. However, I do think it is worthwhile to point out a couple of things to help you better prepare for the exam when it comes to meiosis and variation. I will do this mainly through a couple of images presented to you in class by Professor S.
A Blend of Images Lectures 4 & 5...
On the left is one of the main images that I built my Lecture 5 Blog around. It was also used by Professor S in Lecture 3. Let me be clear about this: This image shows one version of meiosis.Brett, what do you mean it shows "one version of meiosis?"
Well, it turns out that in Lecture 4 Professor S showed you another version of meiosis. The slide that he used to show you another version of meiosis is shown below on the right. I hope you are able to see it in the image, but take special care to notice that the bottom row of gametes in both of the images are similar and different.
On the one hand, they both show 4 gametes each with a single chromosome inside each gamete--this makes sense because they are both representations of meiosis. On the other hand, look specifically at the colors of the chromosomes in each of the gametes. In the first image (above left), there are 2 gametes with entirely blue chromosomes and 2 gametes with entirely red ones. In the second image (below right), there is 1 gamete with an entirely blue chromosome, 1 gamete with an entirely red chromosome, and then 2 gametes (the middle two gametes) with chromosomes that have both red and blue color in them!
If we could put this in more scientific terms, we could say that the gametes produced by the first version of meiosis (above left) have less genetic variation than the gametes produced by the second version of meiosis (at right). How many types of gametes are produced by the first version of meiosis (answer = two types, red and blue). How many types of gametes are produced by the second version of meiosis (answer = three types! red, blue, red/blue mix #1, and red/blue mix #2).
How is this different combination of colored chromosomes (i.e., this genetic variation) possible given the fact that the original parent cell was exactly the same? (If the image on the right showed the original parent cell it would be the same as the one shown in the image on the left--trust me on this one.)
The answer to that perplexing question was presented to you mainly in Lecture 4 by Professor S. That day, he showed you some slides that had terms such as synapsis, chiasmata, crossing over, meiosis I, metaphase I, and independent assortment. Do you remember these slides? I hope so, but if not you can look up these terms/concepts in your textbook. These are the terms that Professor S used to explain to you how there can be increased variation in gametes as a result of meiosis.
Look closely at the right-hand slide up above. Do you see how down the right-hand side of that slide Professor's S was writing the names of the different phases of meiosis I and meiosis II? These are indications of the exact stages in which increased genetic variation is occurring. Another slide he used that day (shown below at left) illustrates something called independent assortment.
There are no stages or phases or meiosis written on this slide, but maybe that is something that you can do now that you know that this process can also lead to increased genetic variation in gametes.Anyhow, this little diversion from the Lecture 5 Blog ("Why Can't We Be Friends?...Meiosis & Punnett Squares finally shake hands") was necessary to try to tie together some additional images that will be important for exam 1. Now, you should go back to the Lecture 5 Blog and continue seeing if and how Punnett Squares & meiosis will finally shake hands...
No comments:
Post a Comment