Asterix

25. What is the distinction between highly repetitive DNA sequences and single-copy genes?
A. The highly repetitive sequences have greater amounts of guanine
B. The highly repetitive sequences have greater amounts of cytosine
C. The highly repetitive sequences are not transcribed
D. The highly repetitive sequences are not replicated

A and B are not true. D is incorrect because the entire DNA is replicated. The answer is C.

28. What is the advantage of CAM (crassulacean acid metabolism) in plants?
A. It helps the plant survive high humidity
B. It helps the plant prevent water loss
C. It helps the plant survive low light intensities
D. It helps the plant survive when there are low nutrients in soil

Yup, that's the question I believe they removed from the paper since the syllabus doesn't specifically ask about CAM physiology. The answer is B; xerophytes live in very dry conditions and their stomatas only open at night to prevent loss of water during the day.

[In fruit flies, grey body is dominant to black body and normal wings are dominant to vestigal wings]

31. Male flies, heterozygous for both grey body and normal wings, were mated with black bodied, vestigal-winged females. 2000 offspring were counted. The resulting percentage of each type of offspring is shown in the table below.

Resulting Offspring       ][       Frequency
Grey body, normal wings            40%
Black body, vestigial wings        40%
Grey body, vestigial wings         10%
Black body, normal wings           10%

What conclusion can be drawn from the information give above?
A. The genes assort independently
B. A mistake has been made
C. The genes are linked
D. The genes are on separate chromosomes

I'm not too sure about this one, but I'd say the answer is C. If the genes assorted independently, the expected ratio would be 1:1:1:1, which is not the case. I think D implies the same thing as A - genes only assort independently if they are on different chromosomes. It's unlikely that a mistake has been made and therefore I think the answer must be C. The linked genes recombined and hence there are greater numbers of certain phenotypes.

Heh, May 2009, TZ2, P1 I recall doing these.

9. Blood is a water-based transport medium. Which property of water makes it a good transport medium?
A. high specific heat
B. Transparency
C. Versatility as a solvent
D. It has its greatest density at 4 degrees

The answer is C. I put A on the exam, but my teacher said that C was the better answer.

10. If 15% of a sample of DNA is thymine, what percentage of the DNA is guanine?
A. 15%
B. 30%
C. 35%
D. It cannot be determined from the information given.

Thymine always pairs up with adenine, thus the amount of adenine must be 15%. This covers 30% of the DNA, thus 70% are made up by guanine and cytosine. Because G & C pair up, there must be an equal number of each base - 70/2 = 35%. The answer is C.

23. Which of the following conclusions did Mendel make from his experiments?
A. Dominant genes are more frequent than recessive genes
B. Genes are composed of DNA
C. Traits are inherited in discrete units, one from each parent
D. Segregation occurs through meiosis

It's definitely not B because Mendel focused on genetic inheritance and it can't be D either because the process of meiosis was unknown back then. A is incorrect as there are no dominant/recessive genes, only dominant/recessive alleles. The answer is C.

They removed two questions from this exam paper. I believe one of them is the one asking for CAM physiology in xerophytes and the other could be question 9 since A and C seem to be correct.