Midterm Test 2016

Mean after bonus = 19.5/25.

For each question, a brief explanation is provided, so that you can evaluate your own answer.  The number of students selecting various choices is given for answers chosen by 10 or more students (N = 79). 

1	Darwin accepted use and disuse as part of the evolutionary process.
2	Natural selection requires that characteristics be inherited without blending.
3	Weismann posted that germ cells pass on information to somatic cells (56) and not the other way around (11). The link between chromosomes and genes was demonstrated by Morgan (12).
4	The Darwinian dogma is that natural selection is accountable for evolution.
5	The difference in mean length between pure lines is genetically based (50).  The range is due to variance (16, 13).
6	Given the number of length categories, a polygenic system is likely (63), but not a single gene (10).
7	Mutation is the source of genetic variation.
8	The Modern Synthesis is alive and well (51). The Neutral Theory complements evolutionary genetics (17).
9	The Balance Selectionists claim that heterozygosity is actively maintained (49).  A dimeric enzyme never forms a two-band pattern (29).
10	Two of the five loci have a principal allele whose frequency is less than 0.95 (25) and four have a frequency less than 0.99 (18).  Both are correct (36).
11	Here, we cannot count heterozygotes, but we can predict their numbers assuming HW (15). The more alleles and the more equal their frequencies, the higher the predicted heterozygosity (63).
12	It is always easier to conclude that there are many alleles than to conclude that there is only one.
13	The second law of thermodynamics describes the transfer of energy from and to matter. This is fundamental in physics and chemistry (22). Hardy-Weinberg models the absence of evolutionary processes (H0) and is only applicable to sexual, diploid organisms (48). Evolution also happens in asexual organisms.
14	The number of possible heterozygotes is the number of possible, unique pair-wise combinations.
15	p is indeed the proportion of an allele found in the corresponding homozygote (47) as opposed to heterozygotes, such that a rare allele is much more likely to be found in heterozygotes - that's important. p is only a square root in HW populations (23).  One should never assume that.
16	This one was a bit tricky.  Yes, if there are only two alleles, there cannot be more heterozygotes than homozygotes.  However, that does not apply to the case where there are three of more alleles (23).  The maximum heterozygosity is n/(n+1); it increases with the number of alleles (53).
17	The solution here was to calculate n.2pq and look for an excess heterozygotes. 40 is more than 100 × 2 × 0.8 × 0.2 = 32 (41) , but less 100 × 2 × 0.5 × 0.5 = 50 (29).
18	The Wahlund effect is due to the fact that the heterozygosity predicted within demes and averaged out is always less than the heterozygosity predicted for the whole population (57).  It does not matter whether the demes differ because of selection, drift, or anything elsel (18).
19	We must not confuse χ^2 and the associated probability (11) of a type I error, which in this case is 0.67, almost a guarantee of being wrong (62).
20	Good - most people know how to calculate p.
21	Selection can never cause a decrease in mean fitness (12).  Directional selection ultimately causes a loss of genetic variance (67).
22	My students know what evolutionary fitness is. I'm happy.
23	Same comment for marginal fitness.
24	Dominance means equal phenotypes for two genotypes and "against" means a lower fitness (60). Having different fitnesses is not enough (11).
25	The key to this one was to figure out that the mutation is dominant.  We know that because the first individual with the mutation must have been heterozygous and yet expressed the phenotype. Selection is therefore acting against the recessive allele, which, as it becomes rare, will hide in the heterozygous state (36).  Selection against the dominant condition would have operated differently (34).
Bonus 26	Sixty people gave me credit for my quote.  Fourteen chose Wallace, who in fact was one of the advocates of "survival of the fittest.