Download 1. In order to increase the trichome number on Brassica rapa, I

1. In order to increase the trichome number on Brassica rapa, I would do the
following: grow a population of Brassica rappa (BRG0). Take the top X percent of
hairiness (for example, ten percent) of BRGO, then breed that selected population to
produce BRG1. Take the top ten percent of BRG1, then the top ten percent of BRG1,
etc. This will produce a gradual increase of average hairiness over the course of
generational selection.
2. The properties of the original population: 63 had 0-4 trichomes. 23 had 5-9
trichomes. 8 had10-14 trichomes. 5 had 15-19 trichomes. 12 had 20-24 trichomes.
The ten selected original plants which then became the parents of the following
generation had a mean number of 16 trichomes.
The distribution of the offspring generation will probably be greater than the
orginial unselected population mean of 3, but slightly smaller than selected mean of
16: it will increase toward the selected average but will not be equal to the average
of the selecteds. If h2=1.0, that would mean that the phenotype variation was solely
dependent upon genetic variation [Vp=VG] and Xp1=16. If h2=0, then the phenotype
variation solely depends upon environmental variation and Xp1=3. Therefore, I
believe h2 will be between 0 and 1, leaning towards the 1 side (therefore be closer to
16 trichomes than 3) because I think the genetic factor will be stronger than the
envirnomental factor. This slow trend toward a different mean corresponds with a
"soft sweep" effect on a population.
The results support this hunch for the following reasons: the Xp0 = 3, Xs=16 and
Xp1=11. So the breeded generation mean trichome count is 11, which leans on the 16
side but is between 3-16. Therefore, h2=R/S=(11-3)/(16-3)= 61.5% realised
heritability. Yay!
3. As mentioned in number 2, h2=R/S=(11-3)/(16-3)= 61.5% realised heritability. So
the VG influence on the offspring was about 2/3, while the Vp is about 1/3. This goes
to show that genotypes have more influence, IN THIS SCENARIO, than environment.
4. The realized heritablitliy varies from generation to generation because the
"breeders" of a given generation will be different from the preceeding generation
precisely because it is a different generation. Also, the environmental factor will be
different because the second generation cannot be born in the same circumstances
and at the same time as the first generation. These differences are influence the
realised heritability because the "magnitude of selection force" changes, and the
response to the selection force can be influenced by environmental factors.
5. I predict that G6 would have a mean trichome number of 39.5%. This is assuming
that the realized heritability would remain relatively stable at around 61.5%. If so,
then h2=R/S=.615=(X-21)/(51-21). In this case, X = .3945 or approximately 39.45%.
6. The original range of Brassica rapa is 0-24 trichomes. So for microevolution, this
range would not change. But it doesn't stay within this range. However, it can't
really be classified as macroevolution either because the range is only partially
exceed. Therefore, this Brassica rapa study is somewhere in between micro and
macroevolution.
Brassica rapa Trichome Range Trend over Generations
G5-6
G4-5
No Trichomes
G3-4
Trichome Range
G2-3
G1-2
0
20
40
60
X-axis= # of trichomes
Y-axis= Generation number
This show that the range of trichomes changes over time, so in a way it's
macroevolution, but it changes gradually and much of the data stays withing the
original range, making it also microevolution. Therefore, it's somewhere between
the two: 'micmac' evolution.
Week 2 Prompts:
#2 Describing experiment in NY Times article:
This expriment studied fruit flies over 600 generations, studying approximately 250
whole genomes of flies in order to better understand what genetic changes had
occured during the 600 generations. They bred them in populations of about 2,000,
and selected the earliest hatching flies to be the parents of the next generation.
Overall, the hatching time by the end of the experiment was 20% shorter than at the
beginning.
#3: hard vs. soft sweep
A hard sweep is one in which a mutation in a gene takes over the entire population,
so that every memeber has that mutation, thereby elimination all other possible
"competitive" mutations. A soft sweep is when a trait is influenced by many genes
and a tendency toward one gene in particular happens slowly and is not necessarily
complete within that population. By this definition, a soft sweep more accurately
describes our Brassica rapa data because the change in trichome number is
happening slowly, over several generations (although I'm not completely happy
with this answer because "slow" and "fast" are relative terms. Compared to the fruit
fly study, our Brassica rapa change is extremely fast: their data only shifted by 20%
over 600 generation while our range almost doubled in only 6). So I suppose
microevolutiona and macroevolution can only be correctly applied to a situation by
first defining the context. Otherwise, all results will always be micro compared to
some and macro compared to others.
REFLECTION:
Once again the importance of defining a system makes itself very evident to me with
the micro vs. macro debate. This is frustrating, because it would be a lot easier to be
able to simply classify any given experiment as micro or macro and be done with it.
By extention, this necessity to always define a system might be helpful in the long
run, but in the short run (e.g. with questions like these) it complicates the process
by adding in another step. This brings me back to the discussion on "is there truth,"
because we can't easily state anything as being relative to a truth that might not
exist. Therefore nothing is easily defined. Luckily, most people don't think like this,
which makes everyday conversation possible, otherwise we would be so caught up
in trying to define everything before we moved forward that we would get nowhere.
Quite a learning paradox.
I would also like to explore the idea of bioethics as or if they apply elsewhere (e.g.
ideas).