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ExtraPlanetaryExpeditionaryReportMission:Tar’ecNor(PID:22371-01)

Missionleader:Dr.Rothacker

Background: In 2025, an

interstellar expedition to PID 22371-01 isundertaken to theoneplanet intheneighboringsolarsystemsthathasaplanetsimilartoEarth.Tar’ecNoras

it is called, is the third planet of thesystem,orbitingasolarbodywiththestandard stellar classification of G2V(a yellow dwarf similar to that ofEarth’sown).Youareamongtheotherresearchers and scientists along ontheexpeditionwhichincludesagroupof exobiologists and exobotantistswith expertise in biochemistry,cellular biology, genetics andevolutionary ecology (having takenBio1113 you aremore then ready toundertakethischallenge).On arriving, you find a biosphere

with many similarities to our ownearth;itisarockyplanetcomposedofironandotherminerals;watercovers

about 65% of its surface and has a20% oxygen/ 78% nitrogen richatmosphere. The planet was formedabout3.5BYAduringwhichadiversityecosystems and organisms hasevolved. Everywhere you turn thereareuniqueandinterestinganimalandplant-like organisms that areperforming a variety of ecologicalfunctions. The ecologists on theexpedition observed that energyenters the ecosystem throughubiquitous photosynthetic “plants”and the diverse chemoautotrophicbioluminescent primary producersthat look a lot like fungi found onEarth. The rest of this food web isequallyascomplexasanyobservedonEarth, with primary and secondaryconsumers occupying higher trophicpositions. Plants and animals aredependent on one another and willcompetewitheachotherforresourcesincluding space, light, and food, aswell as clearly establishedpredator/prey relationships; with allthese intraspecific and interspecificinteractions there is a clear strugglefor limited resources. Most of theavailablenichespace isdividedupsothat organisms have to competewitheach other for resources. Withinecosystems we see decomposers torecycle nutrients, so that they areavailableforreuse.

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Organisms of the same species

grouptogetherbutdonotseemtodoso formatingpurposesbutrather forcompanionship and protection frompredation, thus many organismsappearsocialandlivingingroups.

ExobiologyMission notes: During

the mission, scientists identify andcatalogue about 310 species of“animals” (see illustrationsbelowforexamples) and an equal variety ofplants andplant-like organsisms. Theorganism found here are diverse,having all sorts of amazing shapes,sizes and behaviors. It is clear thatthey are organisms similar inbiological complexity to ourselves,some even possing a central nervoussystemanddifferent tissuetypesthatdevelop from different germ layers.The odd thing is that they allreproduce asexually and unlike

multicelled parthenogenic organismsknown on Earth, they do not everproduce gametes or undergo sexualrecombination. However similar toother asexual organisms we arefamiliar with, these organismsreproduce by binary fission, buddingand other forms of mitotic divisionwhichresult inthenextgenerationofoffspring. In some cases organismsmake a mass of cells that aresepareated internally in special sacswhichseparate it fromtherestof theanimal and develop into “embryos”that undergo development and are“born”.TheorganismsofTar’ecNorhavea

nucleotide based genetics systemsimilar to ours and is composed ofDNA.TheDNAundergoes replication,transcription and translation, andcells posses the cellular machinery,such as mRNA, tRNA, and rRNAneeded to make proteins. However,remarkably the most curious thingabout the organisms onTar’ecNor isthattheyallhaveexactlythesameDNAsequence; that is, fromthesmallest tothe largestorganisms, simplest to themostcomplexones, theyhaveexactlythe same linear sequence of A’s, C’s,T’sandG’s.FornowwehavedubbedthistheUniversalGenotype.Inotherregards, theDNAis linear,

double stranded, with a sugar

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phosphate backbone held togetherwith-in the linearstrandsbycovalentbondsandbetweenthenucleotidesondifferent strand of DNA by hydrogenbonds. Each and every organism hasthe same exact karyotype, with 39pairs of chromosomes packed neatlyinto a nucleus. In all respects theirmoleculeof“inheritance”isidenticaltoours.[Someresearchersarebeginningtheprocessof testing thathypothesisand making transgenic Tar’ecNorians].Thereappearstobestrongselection

toinordertomaintainthismethodofreproduction. Other members of themolecular genetics team haveidentified cellular mechanisms inplace,whichact to identifymutationsandeliminatethembyrepairingthemordestroyingtheorganismifitcannotbe corrected. Thus the integrity andcontinuityoftheuniversalgenotypeis

maintained. Further research hassuggestedthatallorganismsonTar’ecNor evolved from a single commonancestor which had this now-called

“suicidesystem”whicheliminatesanygeneticallydeviantcellsororganisms;thus through natural selection, thesystemismaintained.Diversification, and subsequent

adaptation to the different habitatsand conditions found on Tar’ec Norhave lead to considerable phenotypicvariation. Molecular cell biologistsalong on the expedition are revealingthat there is a complex cellularmechanism in place to regulate thedifferentiation of cell types found inorganisms and have discovered it isnot too unlike ours; chromosomeremodeling through methylation oftheDNA is common, and cells inherittheir DNA from other cells followingthebasictenetsofcelltheory.Your assignment: Some of the

things we have learned in Dr.Rothacker’sclassarethatevolutionbynaturalselectionisdependentonboth(1) an ever changing environmentwhich applies differential selectivepressures on organisms that possessvarying phenotypes, allowing someindividuals to survive and reproducewhileothersdieoff and (2)ameanstopassonheritablevariation. In the above scenario we have adynamic world with all theingredientsneeded tomakeadiverseand complex ecological community;that is, many different types ofselective pressures and organismsvying for resources! For this reasonwecanassumethatDarwiniannaturalselection and evolution are universalprinciples atwork on this planet too.

ImagefromCampbelletal.

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By now you should be askingyourself how such diversity, with somany different “species”, could haveevolved from a single commonancestorwhilestillpossessingexactlythe same universal genotype as thatancestor? It is clear that there is noshortage of adaptive, heritablephenotypic variation, so your team isassigned to explain how such adiverse and complex genetic andhereditysystemmayhaveevolved.Answerthefollowing(10pts):1. Developahypothesistoexplain

the molecular basis ofinheritance on Tar’ec Nor andidentify the mechanism(s) inusehere.

2. WhatistheheritabletraitifnottheDNAsequence?a. What molecular mechanism

isbeingusedtoregulateandmanipulate the phenotypicdiversityobserved?

b. How is it passed fromparent to offspring? (thinkabout mitosis and why is itthat cells give rise to newcellsofthesametype?)

3. How it is that the environment

can influence the expression ofthegenotypeinsuchawayastogetthediversitywesee?

4. Explainasbestasyoucan,how

is it that theDarwinianprocessofevolutionbynaturalselectioncould have produced this arrayof phenotypes from a universalgenotype.a. Identify what selectivepressure could result in thegreatest amount of extinction-andwhy? That iswhattypeof environment might have

the greatest deleterious effectonsurvival?

5. Let us extend what we knowandlookintothefuture,thatis,what could be the greatestlimiting factor to the heritablematerial / mechanism we findonTar’ecNor?

Your grades will be assessed on

the scientific plausibility of yourexplanations (within the limits ofyourknowledge)andeffort.WEAKeffortswillearnyoua0.MEDIOCREeffortsearnyoua5