SECTION A - Suggested Answers

[thushan]

Hmm, not really...the shell thickness would not increase nearly as much as on the southern population, as gene flow is (in this case) nowhere near as powerful at changing allele frequencies as selection.

Anyway, let's see what VCAA says.

[Jdog]

if you were to mention gene flow had occured, you have to say that the increase in size was only minor, however i think thye will except both answers, if either is backed up with statements about the lack/presence of gene flow.

[thushan]

I think I said slightly in my answer

[cjudd3votes]

Any chance of a SS estimate? Ranked first in cohort for SACs, 137/150 midyear and thinking 71/75 unit 4 :\ hoping high 40s :s

[cypriottiger]

well ive heard that you can get a 50 in bio so long as you lose less then 12 marks on both exams. you've lost 10.5 if ur unit 4 score is accurate, so i guess with med-high A+ on sacs you should be in line for a 50 congrats! but id get second reference if i were you

[cjudd3votes]

  Didn't think I'd be in line for a 50.. was thinking 47/48 but I'd be rapt with a 50!

And just a point on the mussel shell thickness, would it be safe to say that increased competition forced other species that consumed the mussels to move north and thus the thickness of the northern population would increase? 

[Jdog]

i don't know, if mussels can move on purpose?  i don't really know.

[cypriottiger]

umm thats kind of making the assumption that the mussel's knew north was safe....

[cjudd3votes]

No the mussels didn't move, other species that ATE mussels moved north because there were fewer thin shelled mussels in the southern region.

[thushan]

Nice work on your unit 3 and 4 exams cjudd3votes - and cypriottiger is right, you'll be in for a 50

As far as that gene flow question is concerned, it said in the stem that the crabs were unable to move into the northern population (reason was not given)...so I don't think they would pay that sorry :S

[Jdog]

yeah, it said specificically that, the crabs were unable to move past the border.

Don't fret though, thats only two marks, im sure youll still get 71.

i think the two answers they will pay are :

no change, due to selective agent

change, due to gene flow.

[cjudd3votes]

I think this is hard to explain over the internet species other than the introduced sand crab could potentially consume the southern mussels. When the new crab species is introduced, other species which previously consumed thin-shelled mussels were forced to migrate in search of thinner shells. Hence, other species that eat mussels move north, eat predominantly thin-shelled northern mussels which gives the thick shelled mussels the selective advantage. I'm not too fussed, I just wanted over 47 I'm more used to chemistry style marking where you can get 95% on an exam and still be well out of contention for a 50   :buck2:

[thushan]

Fair enough, although that is a bit of a stretch....

And yeah, is chem like methods where if you get like 100% after moderation in SACs and then drop 0.5 marks over both exams you're bumped down to a 49?

[Jdog]

Maybe,

I think your adding new infrmation that wasn't in the question thought , thats my only problem.

[stonecold]

Didn't think I'd be in line for a 50.. was thinking 47/48 but I'd be rapt with a 50!

And just a point on the mussel shell thickness, would it be safe to say that increased competition forced other species that consumed the mussels to move north and thus the thickness of the northern population would increase? 

epic user name!!!