Questions??

Here is a place to post the questions you have as we proceed through to the end of the Winter term. When you post a question, be sure to include you name after the question so we know who it is from. If you think you can answer a question that somebody else has posed, please do so! Use a different color font and be sure to include your name. See example below.

Questions from the Crime Scene Lab
Why did some of our DNA samples not show up at all in the gel? (Claire) The best "guess" would be that you had some "issues" loading the gel. Given that others had DNA from the same suspect, we know that it was not my mistake! ;-) As novices, the class did quite well over all. I would still like to see a scanned picture from somebody posted on the wiki....HINT, HINT! (Mac)

Why in one of the lanes on my gel was there only a big blob near the top of the gel and no bands like I see in the other lanes? (Mr. Mac) It is possible that you did not add enzyme to that sample of DNA and therefore there was no cutting of the DNA. So instead of a bunch of pieces of different sizes, you only have large DNA that has not been digested. (Mr. Mac alter ego)

Why did most of the groups have the third, pink strand fall off the end of the gel, and what evidence could have been found from comparing the pink bars?(Charlie) The pink band was actually one of the tracking dyes that are in the EZVision loading dye. It is NOT DNA. The 3 dyes in the EZVision allow you to monitor the progress of the electrophoresis and know how long to run the gel. The pink band runs at same rate as a piece of DNA that is 10 base pairs in length. The other two track at around 400 and 4000 base pairs. [|Here] is a link to info about the EZVision. (Mac)

Why did the different-sized blobs of DNA sliding along the gel stay in bands and not spread out more across the gel? (Charlie) The shape of the bands are determined by the shape of the wells that the samples were loaded into. The comb creates nice "perfect" bands in the gel. If you leave a gel overnight after running it, the bands do become more spread out as a result of diffusion and would not look as "sharp." (Mac)

Questions from the reading on Chapter 17
I just kinda wanted a clarification on how single-gene traits work. There isn't one from either parent? You are confusing a couple of related things here.....yes, you do get one copy(alelle) of each gene from mom and one from dad....so each single gene you have consists of 2 alelles. And then since there are at most a very small number of different ways one can look like with only one trait, what happens if something shifts the environment or something that requires an adaptation. If there are only one to three different ways an animal can change, isn't that almost impossible for the animal to not become extinct in a matter of years? [Mia] Great question....you have identified a real potential problem if there is a limited number of variations in the population and none of them is "good" for the **sudden change** you suggest. Is this perhaps why species do become extinct? What do you think?? (Mac)

I am still unsure about natural selection on polygenic traits, especially directional selection, stabilizing selection, and disruptive selection. [Ally] Tricky language to keep straight to be certain...hopefully the activities yo will do in class soon will clarify these for you...stay tuned! (Mac)

Many of the physical characteristics that we have are caused by mutations in our DNA but what causes these mutations to occur. [Matt] There can be environmental causes such as exposure to UV radiation or other "mutagens" or there can be mutations caused by mistakes in the replication process when DNA is being copied...you may have discussed these types of mutations when you covered DNA replication but perhaps not...we will see them again, don't worry! (Mac)

Approximately how often does speciation occur within various groups of organisms? (I expect that bacteria speciation is more common then mammal speciation) [Billy] There is no set amount of time....what are the causes of speciation? How frequently do these causes occur? Are they predictable? Why might speciation occur more rapidly in bacteria vs. mammals? Hint: how much time exists between generations? (Mac)

I am still kind on confused about the molecular clock, what it is and what it is used for. [Emma] More of a metaphor than an actual clock. If we can assume a certain number of mutations will occur every time DNA is replicated, than we can use the number of DNA differences between two species as a measure of how much time has passed since they had a common ancestor...longer time the "clock" has been ticking so they will have more differences.(Mac)

How do the directional, stabilizing, and disruptive selection work including how the graphs play a role in determining the selection. Also, how is a bottleneck effect instigated? (Sam) Like with Ally's question, tricky terms that will hopefully become more clear this week....stay tuned. I will let you post the answer as soon as you have a good one! (Mac)