Biology Exam Chat + Exam Copy + Answers (now)

[lilmamba17]

Yep C that's what i was saying.

And I agree ^ I was so stressed, my answer reflected that both die but then underneath I wrote The question did not specify what the trait is or that if they possessed the A allele it would allow for survival and just chucked in the probability for only the recessive surviving.

[lilmamba17]

yeah was C, that was a tough one though, 3 of them at first glance seemed right


i think it should be 50%
and 1/2 x 3/4 = 3/8

after exam went and bought literally $20 of chips from coles ... WHY!!!

Yeah I got that as well. Lets just hope...

[simpak]

mavis got a 50 so hopefully she's right !!! XD

Lol don't quote me on shiz.  But, I really truly believe that you guys are misinterpreting that paragraph.  It's because it's a sydnrome, it might be saying heterozygotes are somewhat affected by some things (ie frame whatever pattern) but that doesn't mean they will die (this is clearly given to you by the VCAA because they say Penny is a heterozygote).  Plus, other resources say it is an autosomal recessive pattern.

[Panicmode]

If it is dominant, it is co-dominant. Since this is not mentioned anywhere in the question, it is assumed that for the purpose of this question it is recessive.

In reality, having one allele causes the bones to be more frail, but does not cause OWLS which is what the question asked.

I'll attach a scan soon.

EDIT:

Scan attached of di-hybrid cross/proof

[nubs]

The gene that controls OWLS was made up of two alleles;

O - does not have OWLS
o - has OWLS

For the purpose of this bio exam and with the information given, this was the most valid assumption

"Lethal white syndrome can be described as recessive because heterozygotes (written Oo or N/O) are not affected by intestinal agangliosis"

It must be an allele because it says she is heterozygous for that condition

If she is heterozygous and alive, it means she is an unaffected carrier. Therefore, the probabilty of a foal not coming to term is 1/4

The second part of this question is therefore, 9/16 as when a suitable di-hybrid cross is drawn, it is shown that 9/16 foal will be phenotypically normal (hence the massive space they gave us)

Or alternitvely; Pr(not affected by HERDS) = 3/4
Pr(not affected by OWLS) = 3/4
Pr (not affected by HERDS n not affected by OWLS) = Pr(not affected by HERDS) x Pr(not affected by OWLS)
= 3/4 x 3/4
= 9/16

That's exactly what I and many others in my class did

[lilmamba17]

lol, not sure you can hedge your bets like that UNLESS they end up accepting both answers cos it's an ambiguous question

Nah definitely didnt hedge my bets after what happened chem unit 3, i put it in the working space area in brackets
Just so they know how stupid the question was.

They will probably have to accept both.

[simpak]

Okay shit I understand now.
This is what it is saying.

Let us consider LETHALITY one phenotypic 'trait' and a special overo-colouring another trait.
With the genotype oo, lethality results.
With the genotype Oo, overo-colouring results
With the genotype OO, normal phenotype results.
We can see that the pattern of inheritance almost looks incomplete if we look at overo-colouring as the trait at hand, but we are merely considering the lethality.

[Panicmode]

Okay shit I understand now.
This is what it is saying.

Let us consider LETHALITY one phenotypic 'trait' and a special overo-colouring another trait.
With the genotype oo, lethality results.
With the genotype Oo, overo-colouring results
With the genotype OO, normal phenotype results.
We can see that the pattern of inheritance almost looks incomplete if we look at overo-colouring as the trait at hand, but we are merely considering the lethality.

Yes, you've got it

[Russ]

I haven't looked at the exam properly because I'm up to my ears in lab writeups but the VCAA very often simplify things for your course, so don't go looking at wiki and applying that to the exam paper because it's entirely possible they're not the same.

Perfect example is the stem cell question you were talking about, without proper clarification in the question, D is technically correct

[simpak]

Yes and that's what the wikipedia article is saying, which is why after you guys were like 'No it says they both die' I spent like ten minutes being like 'have I lost my ability to comprehend English explanation?' because I didn't see the passage as saying that at all.
It's saying that because the gene is pleiotropic, depending on which phenotypic trait you want to consider the pattern of inheritance can appear differently (which again reminds us that genes are not recessive/dominant, phenotypic traits are).

[simpak]

I haven't looked at the exam properly because I'm up to my ears in lab writeups but the VCAA very often simplify things for your course, so don't go looking at wiki and applying that to the exam paper because it's entirely possible they're not the same.

It makes me want to cry.

Anyway Russ has reminded me I HAVE TWO MAJOR EXAMS NEXT WEEK, INCLUDING MY OWN BIOLOGY EXAM, so now that we have cleared this up I am going to go and die doing my own revision in a second.

[stonecold]

Typical VCAA screw up on that question about OWLS.  It is clearly ambiguous.  At uni if you do bio, you will learn about different types lethal genotypes.

As long as you said one of either oo or OO dies, you will be fine.  If you said they both die, then you're going to lose marks.

And from quickly flicking through it, it looked like a pretty shit exam...

[Panicmode]

Good luck mavis, sounds shocking tbh.

[simpak]

However, I introduce another ambiguity into your problem - the question asks about horses dying at birth.  HERDA has reduced life expectancy but only OLWS says 'dies at birth'.

[simpak]

NO PUNNETT NEEDED FOR 1 MARK AMIRITE?

Yep, this is how I have always marked...