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Author Topic: VCE Biology Question Thread  (Read 1269301 times)  Share 

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Reus

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Re: VCE Biology Question Thread
« Reply #2310 on: July 22, 2014, 02:30:36 pm »
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Thanks alot! And another question.
what does it mean when it says "only hemizygous genotypes are possible for sex linked conditions"?
This is because unlike the autosomes of a human the X and Y chromosomes are not homologous (they differ in size, different gene expressions etc). Hence a result of Xb Y can occur as a genotype (just an example). You wouldn't conclude that this allele is homozygous (XX) or heterozygous (Xx) but in fact a hemizygous allele (Xb Y).

It's kind of confusing but once you get your head around it, its simple patterning :P
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vox nihili

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Re: VCE Biology Question Thread
« Reply #2311 on: July 22, 2014, 02:42:31 pm »
+1
Thanks alot! And another question.
what does it mean when it says "only hemizygous genotypes are possible for sex linked conditions"?

So if a gene appears on the X chromosome, you know that in a male, you're only going to get one copy of that gene. In the female, it's all normal.
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Re: VCE Biology Question Thread
« Reply #2312 on: July 22, 2014, 02:46:48 pm »
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So if a gene appears on the X chromosome, you know that in a male, you're only going to get one copy of that gene. In the female, it's all normal.
thanks, and sorry for bombarding you all with questions.
....but here is another one.
could someone please explain the ratio that occurs in a mono-hybrid and dihyhybrid cross eg 1:2:1 or 3:1
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Re: VCE Biology Question Thread
« Reply #2313 on: July 22, 2014, 03:40:05 pm »
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thanks, and sorry for bombarding you all with questions.
....but here is another one.
could someone please explain the ratio that occurs in a mono-hybrid and dihyhybrid cross eg 1:2:1 or 3:1


I think the ratio that occurs in a dihybrid cross is 9:3:3:1.. :)

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Re: VCE Biology Question Thread
« Reply #2314 on: July 22, 2014, 03:53:04 pm »
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I think the ratio that occurs in a dihybrid cross is 9:3:3:1.. :)

Also known as the Mendelian Ratio  ;)
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dankfrank420

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Re: VCE Biology Question Thread
« Reply #2315 on: July 22, 2014, 04:28:02 pm »
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Not really a super-relevant question, but how did people who did the 2013 Bio exam find it? Did it seem easy to you?

Reus

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Re: VCE Biology Question Thread
« Reply #2316 on: July 22, 2014, 04:44:02 pm »
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Not really a super-relevant question, but how did people who did the 2013 Bio exam find it? Did it seem easy to you?
I'd like the answer to that too :D
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vox nihili

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Re: VCE Biology Question Thread
« Reply #2317 on: July 22, 2014, 05:41:05 pm »
+1
thanks, and sorry for bombarding you all with questions.
....but here is another one.
could someone please explain the ratio that occurs in a mono-hybrid and dihyhybrid cross eg 1:2:1 or 3:1

These ratios seem pointless to know, but when you do do a cross and there's something funky going on, the ratio will not be 9:3:3:1 as you'd expect, so you can use the ratio to determine what funky stuff is happening. You don't do that in year twelve, but that's why you need to know them.
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Re: VCE Biology Question Thread
« Reply #2318 on: July 22, 2014, 07:48:48 pm »
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in the polymerase chain reaction, why is it that heat is used to split the two strands of DNA? Can DNA helicase be used instead to make two DNA strands?

howlingwisdom

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Re: VCE Biology Question Thread
« Reply #2319 on: July 22, 2014, 08:24:48 pm »
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in the polymerase chain reaction, why is it that heat is used to split the two strands of DNA? Can DNA helicase be used instead to make two DNA strands?
In order to split the two strands of DNA, the DNA need to be denatured at a temperature high enough to allow the strands to separate (at 95 degrees). I think the reason why they do not use DNA helicase is that the whole process would not occur fast enough (in comparison to simply using heat) to amplify multiple copies of DNA or that they are unable to obtain DNA helicase from bacteria that are able to withstand the high temperatures that occur during the PCR process ( TAQ DNA polymerase is used in the process and is found in bacteria that thrive in hot springs.)...Though my assumptions could be wrong!
« Last Edit: July 22, 2014, 08:27:23 pm by howlingwisdom »
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ravi2

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Re: VCE Biology Question Thread
« Reply #2320 on: July 22, 2014, 08:41:05 pm »
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In order to split the two strands of DNA, the DNA need to be denatured at a temperature high enough to allow the strands to separate (at 95 degrees). I think the reason why they do not use DNA helicase is that the whole process would not occur fast enough (in comparison to simply using heat) to amplify multiple copies of DNA or that they are unable to obtain DNA helicase from bacteria that are able to withstand the high temperatures that occur during the PCR process ( TAQ DNA polymerase is used in the process and is found in bacteria that thrive in hot springs.)...Though my assumptions could be wrong!

so... basically, in PCR, the two strands of DNA have to be split, so therefore high temperature is required, to denature the DNA to allow it to split.
But when compared to DNA replication, the entire two strands are not split, and the strands are just opened up upon the replication fork, so DNA Helicase will suffice. (plz correct me if wrong) and thanks howlingwisdom for your help, greatly appreciated:D

Reus

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Re: VCE Biology Question Thread
« Reply #2321 on: July 22, 2014, 08:54:12 pm »
+2
I just have this weird feeling that in this year's exam we'll be asked to draw the structure of a chromosome  ::) ::)
« Last Edit: July 22, 2014, 09:04:11 pm by Reus »
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dankfrank420

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Re: VCE Biology Question Thread
« Reply #2322 on: July 22, 2014, 09:42:56 pm »
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I just have this weird feeling that in this year's exam we'll be asked to draw the structure of a chromosome  ::) ::)

In one of the previous exams you had to draw out a nucleotide, so you never know.

Anyway, from your previous response, assuming you've done the 2013 exam? I thought it was way too easy...

howlingwisdom

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Re: VCE Biology Question Thread
« Reply #2323 on: July 22, 2014, 10:32:53 pm »
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In one of the previous exams you had to draw out a nucleotide, so you never know.

Anyway, from your previous response, assuming you've done the 2013 exam? I thought it was way too easy...
I think the low level of difficulty was due to the fact that it was the first year of the new study design (and combining of units 3 and 4.) I have a feeling that this year's exam will be more difficult, but hopefully it won't be too bad!
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Reus

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Re: VCE Biology Question Thread
« Reply #2324 on: July 22, 2014, 10:47:13 pm »
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In one of the previous exams you had to draw out a nucleotide, so you never know.

Anyway, from your previous response, assuming you've done the 2013 exam? I thought it was way too easy...
Yes it was hahaha

I think the low level of difficulty was due to the fact that it was the first year of the new study design (and combining of units 3 and 4.) I have a feeling that this year's exam will be more difficult, but hopefully it won't be too bad!
Yep, my teacher said the same thing. It was the easiest exam she'd seen in 10 years. They'll make it harder for us, oh well.  :-X
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