BIOL
2007 - EXAM
FREQUENTLY
ASKED QUESTIONS -- Amanda
Linkage disequilibrium and unlabelled picture
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asked questions
Dear Amanda,
Thanks for your queries:
On the 2005 exam, section C part f) asks you to relate the frequency of
AC
gametes to the coefficient of linkage disequilibrium, D. In the notes
from
class, there is no equation describing how to quantitatively relate
differences between observed and expected genotype values to
D.
The frequencies for gametes are given way up in the second panel (LH side
of first page) of the notes for this lecture. If you know the value of D,
pA, and pC you should be able to calculate the AC gametic frequency, or D from
the allelic and gametic frequencies.
Obviously I am not asking whether we will need to know this for this
year's
exam, i.e. asking about the exam's content, but I would like to know if this
has been taken off the syllabus?
Not as far as I know! It is true that understanding linkage
equilibrium doesn't crop up every year in our exams. But maybe it should! It's
very important in today's studies that map human diseases, and also in many
other fields of genome-scanning and mapping of heritable traits in wild
populations. It's also important that not too many people score 100% in
the calculation question, so we often do ask some obscure things to bring the
average mark down to below 70% (which is a first class or "A" grade in the
bizarre UK system).
Also, in the notes for the lecture on 'evolution of genetic diversity'
there
is a picture of morphs of the Acleris cristana. Is this supposed to be
an
example of an organism whose genetic variation is maintained by
negatively
frequency-dependant selection? I assumed so but it is not annotated and I
don't want to assume wrongly...
You are correct. It's an example of diversifying frequency-dependent selection,
and it is not annotated. In the lecture, I would have pointed out the connection,
even though the slide was unlabelled.
Good luck with your exam.
Jim
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