biol+4+exam+queries

Continue with the exam queries below.

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//A. This is probs one of my favourite questions that VCAA has set cos it is a challenging question that requires you to be very clear on what meiosis does, homologous pairs and mutations by applying your knowledge. Drawing a diagram is a good move, it is what I would have done. The question requires you to work out the four gametes (sperm) produced by meiosis if the male has the translocation (the RHS diagram). It is difficult to explain in words without a diagram so check the diagram that I have made. You just need to keep in mind what is the result of meiosis. They provided you with two possibilitites, the other two are sperm 3 and 4 in my diagram, although which one you decide is 3 and 4 is up to you. The key was realising that when they line up in meiosis 1 chromosome 18 does not have a pair, therefore two of the gametes will be "missing a chromosome and only have either the 9 chromosome or the 9/18 chromosome. VM //
 * Q. (VCAA 2002, Question 1c) Ok i'm not really understanding how all this 'happened'. I tried to draw a diagram of meiosis, but it got really confusing with the different homologous pairs and stuff. I'm just not clear on what exactly is happening here during meiosis. AP**

Yes THANK YOU. I get it now! I think when I was drawing the diagram I kept getting it confused with non-disjunction, which is why nothing made sense. But I understand it now. AP


 * Q.(VCAA 2004, Question 9f) I understand this question and stuff, but are we really expected to go into such detail? I mean I read the answers on the assessment reports and it sounded all complicated. And since on 4% got the 2 marks available, I'm assuming its specificity they wanted. Could they ask something like this again? The question just surprised me a little.**

//A. These "vague" questions are difficult because you need to try and work out what the examiners are looking for in an answer. As VCE biology students you are expected to draw on your background knowledge to come up with a logical answer. BUT in these questions they will most likely provide you with some info to assist you, as was the case here (musculature and weight). So, the only advice I have for these types of questions is to carefully and thoroughly go back to the information given and look for clues. In your answer always try to show as much biological understanding, avoid writing general "layperson's" answers. So, yes they will ask questions that challenge students (they need to separate you guys) to see who can apply knowledge in a new situation and draw on ideas. VM //

Q. exam 2004 Q2a, i know its autosomal but im dont know if its recessive or dominant, the answer said its dominant but shouldnt 3 out of the four children have the condition then, but then if it was recessive only one of the offspring could get the condition, so it sort of makes sense then. Is that how i have to look at these quetsions.

//A. First of all I assume it is Q2b i and it is important that you are referring to the pedigree they drew, not the one you drew in part a. I am not sure why you think 3 out of the four children should have the condition. **Do not rely on phenotypic ratios in pedigrees**, these are only expected ratios AND a pedigree shows you who has what. It is AUTOSOMAL DOMINANT because of this simple fact. Both parent have the condition, so if it was recessive the parents would have genotypes of 'pp' (using P and p). Now if both parents have these genotypes then all their children can only ever get the 'p' allele and therefore will ALL show the condition (this would happen whether it was X-linked or autosomal). This is not the case. Therefore it must be dominant because then the parents can be heterozygous and therefore produce children with the condition or without the condition, as is the case. It cannot be X-linked dominant because the father is affected, therefore having the 'p' allele which he will pass on to **all his daughters**. We have already established it is dominant which means all daughters would have to have the condition, this is not the case. Thus we are left with autosomal dominant. So, when analysing the pedigrees I think the most useful thing to do is to assign alleles and start working out genotypes of individuals to see if they can fit a certain type of inheritance. VM //


 * Q. (VCAA 2005, Q1c) Just wanted to be sure, if this was the correct way to draw that diagram for meiosis. Of course it would look much neater if I drew this on the actual exam.**

//A. It is important to read the question so as your diagram answers what they asking, in this case production of gametes. It is good that you used their shading and non-shading key. YOU MUST BE CONSISTENT WITH THE INFORMATION THEY GIVE YOU. Your diagram is fine in that you have shown two intermediate cells, then sister chromatids separating in each of these to produce four gametes. BUT the most important part of meisois, the part that separates it from mitosis is the 1st stage, which you have not drawn. Your diagram needs to include the homologous pair lined up on either side of the equator or at least each "double-stranded" chromosome of the homologous pair being pulled to each of the poles. Finally, a diagram without labels is a risky thing to do. Make sure you do this. You are showing understanding and this gets you marks. VM //