Genetics option (1 Viewer)

[elisabeth]

C'mon, my fellow genetics guys and girls, what did you all think of this year's paper?

I was actually really worried and stressed because I hadn't really learned about all of the 8th part of the syllabus, which had never been tested. But nothing on that! *all info on HOX genes flows out of brain* But alas, I'd been cramming this to the detriment of other dot points.

I was quite suprised that it seemed to be mostly questions which had been asked before, unusual considering there's a lot of hard stuff that has never been included.

What were you ratios for BbRr? And what did you put for the DNA model? I said it wasn't useful, because there was nothing to represent sugar/phosphate bonds; no different scale for bases/sugar/phosphate and no complementary structures to show that A could only join to T, C to G... but only because I couldn't think of more than one reason why it was useful. Not sure if that's right.

Anyone had their bio teacher have a look at it?

Is it alright if we post the Qs?

(a) During your study of this option you constructed a model of DNA. The diagram represents a model made by a student.

(i) In this model, name TWO of the parts labelled X, Y and Z. (2mks)

(ii) Is this a useful model of a DNA molecule? Support your choice with two reasons. (2mks)

(b) The diagram shows the arrangement of human chromosomes. A chromosomal abnormality is circled.

(i) Determine how many chromosomes this person has and name the type of chromosomal disorder. (2mks)

(ii) Compare the effect of germ line and somatic cell mutations on a species. (4mks)

(c) The HGP has identified the DNA-base sequence of all human chromosomes. A significant amount of work still needs to be done so that this information can be used to benefit humans. Using examples, evaluate the limitations and expected benefits of the HGP. (7mks)

(d) Indian corn has four grain types that involve combinations of colour (b) and appearance (r). Four genes are involved, whicha re located on two pairs of homologous chromosomes (each gene on a separate chromosome). The alleles are:
B = black
b = yellow
R = round
r = wrinkled

(i) The table below shows the results of a dihybrid cross between two hererozygous parents (BbRr x BbRr).
Grain phenotype Observed number of offspring
Black, round 144
Black, wrinked 48
Yellow, round 48
Yellow, wrinked 16
Total 256
Using this data, calculate the ratio of phenotypes in this cross (1mk)

(ii) If, however, B and r are on one chromosome and b and R are on another, draw a Punnett square of a dihybrid cross (BbRr x BbRr). Include the phenotypic and genotypic ratios of the offspring. (3mks)

(iii) Explain how cross-breeding experiments can identify the relative positions of linked genes. (4mks)

 

[kyu_chan]

Me too me too!! Especially HOMEOBOX!!!! wahahahahahahaha!! Was worried sick but hell yeh, this paper was good!!

My ratio was weird.. 1:2:1 for the Br thing... What did you guys get? I doubled check that because it looked wrong... But then it isn't because I remembered linked genes for the double cross thing

For me, the model was effective sonce it allows you to visualise the concept and pattern of the dna molecule... and the different and complementary bases (different colours) allows us to see the pairings etc... I don't know, just did anything. I think it's ok unless you havent stated 2 reasons why...



edit: spelt homeobox wrongly ^^'' hahaha

 

[bscienceboi]

Post the question if you can.

 

[melimoo]

i said the model wasn't good cause it didn't demonstrate the double helix shape, it was 2D, static and it didn't portray the nature of hydrogen bonds (ie easily separable)
and i said it wasn't labelled either = confusion

and i too am so stoked there were no HOX or anyhting. i had nooo freaking idea and i spent like 5x as much time on genetics than i did for anything else literally

 

[kyu_chan]

i said the model wasn't good cause it didn't demonstrate the double helix shape, it was 2D, static and it didn't portray the nature of hydrogen bonds (ie easily separable)
and i said it wasn't labelled either = confusion

and i too am so stoked there were no HOX or anyhting. i had nooo freaking idea and i spent like 5x as much time on genetics than i did for anything else literally

Ohh! We made our model with lollies (on th last lesson of biology) so I said it can twist and demonstrate the double helix... and we used toothpicks to join the lollies together... shit... would they know what I'm alking about since most of you guys did it 2D?

And me too, I spent so much time on genetics but thats the course I want to get in so it's normal ^^

 

[elisabeth]

Yeah, I got a 1:2:1 ratio too! I looked wrong but then I remembered that it's only a 3:1 ratio if the linked ones are BR and br, ie. both dom/both recessive. Hope that's right.

Anywho, soooo relieved they didn't ask for part 8!!! Sucked in people who will probably get it next year!

 

[kyu_chan]

ahahahahahahahahhaa soooooo truee!!!!!

btw, I'm disappointed that there were no dna fingerprinting questions... or recombinant dna questions... I was hoping for those questions for big fat 6 marks and stuff hahaa

but happy that there were no tissue culture, nuclear transfer and embryo splitting... i hate that stuff... oh yeh, that selective breeding *sighs of relief*

 

[The_highwayman]

I said it was an effect model Because:
i) It was simplistic in design and so did not allow great confusion
ii) It allowed components to be distinguished basedon their patterns.
(and i added a third just in case [i had an hour to use up]) iii) it was inexpensive to make, all you needed was a pencil.


Edit: Oh yeah, my ration was also 1:2:1. Which i tripled checked coz i thought it was weird (ie: i thought i was meant to get a 3:1 :S)

I liked the 7marker: HGP limitations and expected benefits. I also liked the relative position of linked genes question. All in all, a nice option paper.

 

[chingly_choo]

Me too me too!! Especially HOMEOBOX!!!! wahahahahahahaha!! Was worried sick but hell yeh, this paper was good!!

My ratio was weird.. 1:2:1 for the Br thing... What did you guys get? I doubled check that because it looked wrong... But then it isn't because I remembered linked genes for the double cross thing

For me, the model was effective sonce it allows you to visualise the concept and pattern of the dna molecule... and the different and complementary bases (different colours) allows us to see the pairings etc... I don't know, just did anything. I think it's ok unless you havent stated 2 reasons why...



edit: spelt homeobox wrongly ^^'' hahaha

I got 1:2:1 as well, so yeah. I had no idea and spent ages doing the dihybrid cross of the original one. Then realised I was doing the wrong thing and had to cross out all my neat, neat, NEAT working. But Iended up with that ratio and was like, if its wrong I DON"T CARE!

The model wasn't very effective for me. I was so angry at it (all the different lines and crap started doing my head in!) and said it wasn't very good cos it was too simplistic and did not accurately reflect the complexity of the double helix. Also said without a key was worthless as didn't know which bases were which and thus rendered the diagram useless.

Ha! Only realised the existance of homeobox genes this morning and went well, too bad if they're in there. AND THEY WEREN"T! So happy

 

[The_highwayman]

i still dont know what these homeobox genes are that u speak of

 

[elisabeth]

i still dont know what these homeobox genes are that u speak of

Who cares, now you don't need to!

 

[The_highwayman]

Who cares, now you don't need to!

HOORAY! *Jumps up and down*

 

[ball_of_anger]

For the question... "Is this a useful model of a DNA molecule? Support your choice with two reasons."
I used my history (mod, extension)to answer. Said something like… the model is partly useful because it has + and – aspects:
+ Simple, easy to understand
- Does not have 3D and cannot fully understand double helix principal.
Is this an acceptable answer in bio? Or should it be more YES or NO.??

 

[elisabeth]

No idea. I said it was a little useful but overall it was too simplistic thus not useful... tried to make it more clear cut bio style and gave two reasons for a NO answer. Ask your bio teach.

 

[Blackroze]

I said the DNA model was useful because it simplified a complex theory thus increased understanding. Then added something about sucessfully representing nature of DNA structure etc.

Thank goodness there were no hox questions! I really was expecting them because they've rarely been tested (if ever?). The examiners had to pry my notes from me as I desperately tried to remember the gene cascade buisiness. My ratio was 1:2:1 also (hurrah) and yes I agree that the HGP limitations was a nice question. Basically could have made it up using some common sense ^_^ Very impressed overall.

 

[daemon22]

I said it was an effect model Because:
i) It was simplistic in design and so did not allow great confusion
ii) It allowed components to be distinguished basedon their patterns.
(and i added a third just in case [i had an hour to use up]) iii) it was inexpensive to make, all you needed was a pencil.


Edit: Oh yeah, my ration was also 1:2:1. Which i tripled checked coz i thought it was weird (ie: i thought i was meant to get a 3:1 :S)

I liked the 7marker: HGP limitations and expected benefits. I also liked the relative position of linked genes question. All in all, a nice option paper.

ahaha.. that test was tops, I wanted dna fingerprinting and sequencing though :S

but 1:2:1 is right, it's what I got... and I studied linked genes by asking the teacher the morning before.. flannagan's tops! watchu guys write for the search for better health 8 mark question ppl?

 

[daemon22]

i said the dna model was good because:
1. it accurately showed that the nitrogenous bases are joint to sugars which are joined to phosphates
2. consistent base pairing suggests it correctly shows dna base pairing

 

[Kazness]

no complementary structures to show that A could only join to T, C to G...

It kinda did- I wrote that it was a good model because it showed the three hydrogen bonds between cytosine and guanine, and the two hydrogen bonds between adenine and thymine.
Plus a second reason which I have now forgotten.

I wanted dna fingerprinting and sequencing though

I was able to weave it into the HGP question, while talking about understanding the function of previously unknown "Introns" and "tandem repeats" and how they will (with further research) be useful for more than just DNA fingerprinting. Blah blah blah...

I really liked the Genetics option, and agree with all of you in the "thank God no HOM or HOX stuff" especially in regards to evolution! Phew.

 

[elisabeth]

Haha, damn, didn't even notice that. But still, I think cause I wrote about complementary structures - ie. lock/key type shapes - that should be valid. Because the diagram could have had 3 bonds between each and would still have 'fit'... you know what I mean?

 

[Bboymot]

I wrote the dna model is bad because it does not differentiate between the structures of Deoxyribose sugar, phosphate bonds and bases.

I also said it was bad because it is impossible to tell which base is which, although they allign correctly you cant tell which one is atgc...