1. mass extinctions to speciation
2. Field trip review – decompress
10/24- Wednesday Homework:
Complete form after the paragraph below.
Life continues to evolve within a changing environment.
Speciation and extinction have occurred throughout the Earth’s history, and life continues to evolve within a changing environment. However, the rates of speciation and extinction vary. Speciation can be slow and gradual or, as described by punctuated equilibrium, can occur in “bursts” followed by relatively quiet periods. At times of ecological stress, extinction rates can be rapid, and mass extinctions are often followed by adaptive radiation, the rapid evolution of species when new habitats open. Scientific evidence, including emergent diseases, chemical resistance and genomic data, supports the idea that evolution occurs for all organisms and that evolution explains the diversity of life on the planet.
A species can be defined as a group of individuals capable of interbreeding and exchanging genetic information to produce viable, fertile offspring. New species arise when two populations diverge from a common ancestor and become reproductively isolated. Although speciation can occur by different processes, reproductive isolation must be maintained for a species to remain distinct. Evidence that speciation has occurred includes fossil records and genomic data.
End of Wednesday..
10/25- THursdsday – period 7 – Academic Study Hall
1. Write your notes into SHARED Google Doc from our Cornell Visitation
2. Make a second submission to last nights form.
2. Review weekend forms toughest questions, Chapter 22/23 quiz.
3. Continue with Speciation presentation.
4. Fast Plants – Hardy Weinburg-
10/25 – Thursday Night HW:
1. Write your notes into SHARED Google Doc from our Cornell Visitation
2: Please use the form as your guide to view the following videos and complete the form:
*Connections – Todays FAST PLANT Calculation Demo
Today we looked at the second generation of the of our Fast Plants and we discovered and calculated the frequency of the Non-purple Stem Color allele (q) which is a recessive allele.
We did this by recognizing that our F1 population were 100% heterozygotes, thus every individual had the recessive (q) AND the Dominant allele (p).
Have all heterozygote individuals thus ensures that our: F1 generation = q = . 5 and q = .5
We wanted to see if there was micro evolution at the Stem Color allele in the second generation.
Remember the the Hypocotyl – (stem below the cotyledons) was
Purple Or Non- purple (green)
ANL/anl or ANL/ANL anl/anl
ANL is the p anl is the q
Now we are after the q for the second generation to see if there was EVOLUTION but we had some work to do calculate the q.
NOW the jumping off point is the homozygous individuals BECAUSE WE KNOW THEIR DEFINITE GENOTYPE (q2) if we identify the expressed recessive phenotype. Homozygous and Heterozygous genotypes share the same phenotype so we cannot get allele frequencies directly from those individuals.
This was our class data for the F2 generation:
| Green Stem *Individuals/ total
q = .65
|q = .65
*We multiply both the numerator and denominator to get total alleles (each individual has 2 chromosomes)
Lets compare the 2 generations:
q= .5 .65
The second generation q changed!! We are not in Hardy-Weinberg Equilibrium and thus there is evolution.
Only 3 things that will cause evolution. Gene Flow, Natural Selections and Genetic Drift. Clearly there were no pollinators (bees) that had pollen from other FAST Plants fromother because we had a small population we had Genetic Drift.
Using the AlleleA1 simulation, Genetic Drift of allele A1 (p) or the dominant allele LEAD to the “death of A1 alelle” after 300 generations of 400 individuals. This is due to random events in producing gametes in meiosis AND in Random fertilization.
This what is meant by the drift! With no other forces working, No Natural Selection, Gene Flow, or inbreeding an allele is lost from the population. Remember we are tracking only 1 allele and that is very possible that this happening at other alleles in the genome of the species.
Genetic diversity is decreasing and this population is becoming less like the populuation it once belonged to.
Genetic Drift can lead to loss of alleles as I have shown you in the Excel Spreadsheet or the simulation that I have demonstrated for you. If these alleles are connected to ANY part of the reproductive genes then Speciation can occur as reproductive isolation will occur between different populations of the same species.
Natural Selection, Gene flow, and Genetic Drift can all lead to decreased genetic diversity in a population. These forces that cause relative allele frequencies to change at the population level can also influence the selection forces that shape them over successive generations. Remember that Evolution is not perfect and reproductive success is determined by alleles that are best favored for the current environmental conditions. These best favored alleles which are selected for due to the selective pressure by the environment of are ones that ARE THE BEST AVAILABLE alleles that the population currently has to choose from. Remember that only Natural Selection is adaptive but this adaptation occurs from what alleles are available and these available alleles are subject to change by the action of Gene Flow and Genetic Drift. So Gene Flow and Genetic Drift are not adaptive but they shape Natural Selection by providing the choices!!!!
Speciation, or reproductive isolation that occurs from the loss of alleles in the reproductive process, almost always occurs from small groups
AND the forces that make Speciation possible are the forces that make a species susceptible to extinction.
Lowering the genetic diversity through Stabilizing Selections or through Genetic Flow and Genetic Drift essentially decreases the variety of alleles that could potentially give the population the ability to survive when environmental conditions change.
THIS IS WHY MOST SPECIES BECOME EXTINCT AND THIS IS THE REASON OLDER SPECIES STILL PREVAIL TODAY.
FOR EXAMPLE: The current 3 elephant species that inhabits Africa and Asia have a distant relative in the
Manatee which is its the closest living ancestor.
What forces are at work?
Let us revisit a phylogenetic tree of Evolution of Humans (Hominids):
Why is the Chimpanzee still with us?
Why have so many of our early ancestors gone extinct?
Notice that bipedalism was an adaption that occurred long before large brains?
What possible selective pressures made bipedalism an advantage OR do you think that bipedalism was just a non adaptive form of evolution?
A very interesting article on this last question:
End of Thursday.
10/26- Friday- period 7/8
1. Review Evolution and Speciation Forms (Wed night homework – 2 subs)
2. Review Plankton Form (Last Nights Homework – 1 sub)
Notes from connections above will Allele a.
3: Genetic Drift/Natural Selection/Gene Flow —-> Speciation ——> Extinction ——> Adaptive radiation
1. Started Brine Shrimp Class Data compilation with Excel.
4. Brine Shrimp Data collection /graph and data table design