Here we go again- Exam II for Genetics

[WindRavenX]

After the delightful first Exam (and by "delightful" I mean "failed"), I find myself panicking at the realization that yes, this Friday, the LAST DAY BEFORE SPRING BREAK, there is another Exam.
Sigh. I can't do anymore Yeast genetics. I'm confused, I need to talk to the professor, and I'm freaking out.
ARgghh!I need some mad good vibes DUers, coz I'm getting my ass served here x( x(

[legally blonde]

1. AAAHHH--Genetics

I remember taking genetics when i was a sophomore (I have my degree in biology and psych) - I know what you are going through. Genetics was never one of my favorite classes, either. You should definitely talk to your professor. Maybe you should try studying with a few others in your class (caveat--make sure they are studious). That usually helps me work out difficult concepts (transcription and translation are tricky!).
Good luck! :pals:

[WindRavenX]

2. tetrad analysis

I understand how to calculate map distances based on the # of PDs, TT, and NPDs, but I can't read the charts that show the traits! x(

[legally blonde]

3. Oiy!

I barely remember that stuff--that was six years ago for me! My brain is now full of boring law crap so I wouldn't remember that anyway!
You should definitely make an appointment with your professor--ASAP!

[Sufi Marmot]

4. If it's any consolation...

yeast geneticists haven't done this for years, what with the entire yeast genome in hand. I had to do it in my grad school genetics class and then promptly forgot how to do it...

What exactly is it that you don't understand - I might be able to help...

-SM

On edit: I suppose that scientists who study genetic recombination might do PD:NPT:T analysis, but normal people don't.

[sir_captain]

5. Ah...I've been doing some genetics myself, lately

And I agree with you...I haven't yet figured out why I should be interested in Yeast tetrads. Though I suppose they're better than bread mold. Do you have to do that too?

But anyway, what are you confused about? Maybe we can find some bio types here on DU to help you out!

[WindRavenX]

6. how to read the charts that list...

...whether a progeny of a mating if PT, NPT, and TT. I understand how to calculate the distance between them if I'm given numbers...but argh.
I just want to stick to virology and evolution...this shit is killin' me! x(

[Sufi Marmot]

7. Do you know the starting genotype of each parent in the cross? n/t

[WindRavenX]

8. well, that's the thing

Yes, reading my lecture notes, they obviously give us the genotypes of the parents and the chart of the +/- traits for each progeny. I'm concerned with my ability to read these charts during an exam, which is why I'm going to my professor.
I am developing an intense dislike of yeast and E.coli....

[Sufi Marmot]

11. Yeast Genetics 101...

1) For the progeny, if PD = NPD, then the two markers are unlinked (could be on separate chromosomes, or far apart on same chromosome)

2) If PD > NPD, then markers are linked; if 100% PD then complete linkage

3) Tetratypes arise from a crossover between the centromere and one marker. If your cross has no tetratypes, then both markers are CEN linked.

4) Map distance = cM = # of recombinant spores/total progeny X 100. If A is CEN linked you can determine whether B is also. For instance, if from 100 tetrads you have 45 PD tetrads, 45 NPT tetrads, and 10 T tetrads, you know that since PD = NPD the two markers are unlinked. How far is B from the CEN?: 10 T tetrads = 20 recombinant spores; 400 total spores (progeny) = 5 cM. Important: If B was not CEN linked then you would get PD:NPT:T in 1:1:4 ratio.

PD:NPT:T = 1:1:4 - 2 markers unlinked, no CEN linkage

PD:NPT:T = 1:1:<4 - 2 unlinked, CEN linkage

[WindRavenX]

14. you guys ROCK!

Seriously, thank you all.
Genetics has been a real struggle- I'm much more of an evolutionary bio or ecology type biology. Thanks again!

[Sufi Marmot]

15. I knew there was a reason I saved my advisor's obtuse genetics notes...

Good luck!

-SM, who has dissected many, many tetrads in his life...

[Sufi Marmot]

17. Things get more complicated if you have multiple crossovers...

...did you guys cover that in class? (I'll spare you the pain if you don't need to know for the exam...) :-)

-SM

[sir_captain]

12. Ok, the thing to do here

is to look at two of the traits at a time. So if the traits are ABC, you'd look at A-B, A-C, and B-C all individually. Just make a chart of these two-trait comparisons as PD, NPD or T and then you can plug that info into the RF equations.

[sir_captain]

9. Think of it this way:

Hopefully you won't even need the charts, as long as you know the parental genotypes.

If the parentals are, say, ABC/ABC and abc/abc, you're all set.

The PD would be: ABC, ABC, abc, abc, since all four asci have the same genotype as one of the parents.

NPD would be something like ABc, abC, ABc, abC because *none* of the asci have genotypes the same as the original parentals.

Tetratypes are a mix, you you'd end up with something like ABC, abc, AbC, aBc. Basically, if you see two genotypes that are parentals, and the other two are not, you know you've got a tetratype.

Does that help at all?

[WindRavenX]

10. yes!

The problem is translating what you said into how the professor drew it onto a chart- I get the deffinitions of what each tetrad is, but I now need to convert that to what is represented in the chart.
Thanks a lot though! :hi:

[sir_captain]

13. Good luck!

Try not to get too stressed--even if it doesn't go quite as well as you want, remember that no single exam grade, or even any single class grade is going to make or break your academic career. I was a history major in college and have only now gone back to do all the science--just take your time with it and thank god that we exist under the american higher education system that doesn't pigeon-hole us academically based on one or two tests.

[WindRavenX]

16. I know

I'm not going to med school or anything so I just want to pass this mfing class- but I BOMBED the first exam, and I'm freaked out that I'll fail this class....

[sir_captain]

18. I hear ya

I'll keep my fingers crossed for you! :pals:

[WindRavenX]

19. thank you

again, you guys are the best :7

[Sufi Marmot]

21. How did he represent the tetrads? Did he use actual data?

Sometimes they make you identify the type of tetrad by assessing the markers for each spore and comparing with the parents.

-SM

[Radical Activist]

20. I'm sorry but

I'm too distracted by your "getting my ass served" comment. I also know nothing about genetics, but good luck.

[WindRavenX]

22. failing an exam = me getting served

I'm letting goddamn YEAST beat me! Argh! How humiliating!

[Radical Activist]

23. I was just trying to

make it sound dirty. Nevermind me.

[Robeson]

24. Genetics are a breeze....

...its like 1,2,3. You can do it...