Bio4250 midterm questions (2025)
1) I may change the numbers to be used in any of the numerical calculations given below. I may require an answer to one question in particular, with a choice of any two others.
2) Your answers should be handwritten, and about the length of one 8.5 x 11 page. Write each answer on a separate page.
3) You may bring one-half of an 8.5 x 11 sheet of paper with notes (on both sides); please do not try to cram all of the answers in the smallest handwriting possible. Hand in these sheets with your answers.
BIOL4250 - Sample Midterm Questions
Prepare answers to ALL of
the HOMEWORK questions below. For the exam, I will choose
FOUR: you must answer any THREE in the75 min exam Period. Show
your work.
[I
suggest that you not use calculators]
1.
Prior
to the advent of molecular data in the 1960s, it was assumed
that the large organismal differences between humans
relative to other apes (including chimpanzees
and gorillas)
were due to a large amount of genetic change along the human
lineage. (a) Test this
hypothesis by counting the number
of SNP changes among the three pairwise combination of
primate species A, B, & C as provided at the
time of the test. Report these
numbers. (b) Do the data support or reject the
hypothesis?
Explain.
2.
William J
Spillman was
an American agronomist who in 1901 observed experimentally
what would later be called Mendelian ratios. Answer the HOMEWORK question here
on his crosses. Write your answer as a teaching exercise for
a Biol2250 student
trying to understand Mendelian ratios.
3.
With a sample
size of n = 100, is a
ratio of 58:42 sufficient to demonstrate a
significant deviation from an expected 50% : 50% ratio
at p = 0.05? Explain,
with numbers. (2) With n=100,
what is the minimum deviation from
expectation that could be detected as statistically
significant at p=0.01? From the
formula for Chi-Square, show algebraically what
the minimum deviation is. A table of Chi-square values
will be provided.
4.
(a) Calculate Hexp
for a locus with 50 alleles
at equal frequency: show your work. (b) How many genotypes
are there at such a locus? (c) Calculate Hexp for a locus
with one allele at q = 0.5,
and another 9,
all at equal frequencies. Show your work.
[Hint: use appropriate shortcuts. Don't use a
calculator].
5.
Show the
derivation of the Hardy-Weinberg Theorem, in
terms of 
p = (p' -
p).
6.
The course
notes state: "The genetic dominance relationships
of two alleles A & B at a locus with
respect to fitness are fixed genetically, according
to whether the AB heterozygote is more similar to
the AA or to the BB homozygote. It is not
determined by the phenotypic values themselves."
Explain the idea of genetic
dominance, and in doing so explain the
difference between genetic
dominance and phenotypic values.
7. For a graph of the fate of a
rare allele B under positive selection,
the
course notes state "The
information in the graph also shows the fate of a common
allele A under negative directional
selection, IF the vertical (Y) axis
were inverted top to bottom (1 
0) and labelled f(A)
= p. That is, the behavior of the two alleles
at a locus are complementary for
any particular dominance model." For
such a locus, show that the graph for A
dominant to B is in fact complementary to the graph of
B dominant to A.
If you wish to make a numerical argument, let the fitness of
the dominant phenotype be twice that
of the recessive phenotype.
8.
For each of
the graphs of q = f(B), identify which
mode of selection is acting to produce change in q. Identify
and explain the features of the curve of q over
time that allow you to recognize the mode of selection. The
particular graphs to be used are a
work in progress.
9.
For a
phenotype due to semi- or incompletely dominant alleles
with Additive or Genic selection, for an
initial f(B) < 0.01 and s < 0.5, use the GSM
worksheet in Excel to run the (1) Additive and (2) Genic selection schemes in
the table provided. At what values do the curves deviate and
(or) converge on each other? Why?
10.