Breeding dragons: investigating Mendelian inheritance

Transcription

1 Breeding drgons: investigting Mendelin inheritnce Mendelin inheritnce cn be tricky topic to tech, but Pt Tellinghuisen, Jennifer Sexton nd Rchel Shevin s memorble drgon-breeding gme mkes it esier to understnd nd remember. Imge courtesy of julos / istockphoto REVIEW Biology ges s secondry-school biology techer I hd never come cross the ide of teching genetics using mythicl cretures, but fter my initil surprise, I relised tht using the genetics of drgons ws perfectly coherent with the scientific fcts... nd relly good fun! The ide of rndomly choosing genes nd looking for the resulting trits of bby drgons is ingenious nd effective t the sme time. Even if they ren t rel, drgons cn help to rise interest in topic generlly considered boring (t lest by students) nd cn convey scientific concepts s well s rel orgnisms like Mendel s pes do. I recommend this rticle to primry- nd lower-secondry school biology techers willing to ddress the bsics of Mendelin genetics (genes, lleles, genotype nd phenotype, dominnce, meiosis nd breeding) in novel nd plyful wy. The ctivity could be crried out very esily in the clssroom with prcticlly no equipment. Suitble comprehension questions include: 1) Drgons hve: ) seven chromosomes b) seven genes c) seven pir of chromosomes d) seven lleles. 2) When you breed drgons, the number of chromosomes of their offspring: ) is divided into hlf b) remins the sme c) is doubled d) depends on their sex. Giuli Reldon, Itly Imge courtesy of lexsey / istockphoto 40 Science in School Issue 18 : Spring 2011

2 Teching ctivities Drgons my be mythicl nimls, but they cn still be good tools for investigting Mendelin inheritnce. In the following ctivity, students will breed bby drgons, using pper chromosomes to determine the genotype nd phenotype. The ctivity hs been tested with students ged 12-13, nd generlly tkes one lesson bout 45 to 60 minutes. Mterils For the whole clss DN model picture of chromosome For ech student set of chromosome strips in two colours (14 pink strips for the mother nd 14 blue strips for the fther) student worksheet Cryons (t lest four colours) The chromosome strips, Tbles 1-3 from the worksheet nd the bsic drgon drwing cn be found on pges 42/43 or downloded from the Science in School website w1. Procedure Using the informtion below, introduce the drgon story nd the required bckground for the ctivity to the students. Then hnd out the mterils nd let the students follow the instructions on the student worksheet. Tbles 1 3 cn lso be downloded from the Science in School website w1. The story Drgons re curious type of creture. mzingly, though, their genetics is very similr to tht of humns or even guine pigs. Mny schools keep pet guine pigs, but wouldn t it be much more exciting to keep herd of drgons? Unfortuntely, drgons re very expensive, so your school cn only fford two one of ech sex. The purpose of this ctivity is to determine wht kinds of drgon you Imge courtesy of Drryl Lej, NHGRI / NIH gene Deoxyribonucleic cid (DN) Chromosome How DN is pckged into chromosomes (not to scle) could hve in your herd when (or if) your two drgons decide to mte. Bckground for the students Ech cell in ll living orgnisms contins hereditry informtion tht is encoded by molecule clled deoxyribonucleic cid (DN): show students the DN model. DN is n extremely long nd skinny molecule, which when ll coiled up nd bunched together, is clled chromosome: show students the picture of chromosome. Ech chromosome is seprte piece of DN, so cell with eight chromosomes hs eight long pieces of DN. gene is segment of the long DN molecule. Different genes my be different lengths nd ech gene is code for how certin polypeptide should be mde. One or more polypeptides form protein, which cn generlly be sorted into two different types: those tht run the chemicl rections in your body (enzymes), nd those tht re the structurl components of your body (structurl proteins). How n orgnism looks nd functions is result of the cumultive effect of both these types of protein. ny orgnism tht hs prents hs n even number of chromosomes, becuse hlf of the chromosomes come from the fther nd the other Imge courtesy of Nicol Grf Different lleles of the sme gene (not to scle) hlf from the mother. For exmple, in plnts, pollen grin is the pternl contribution nd n ovule is the mternl contribution. These two cells combine to mke single cell, which will grow into seed (the offspring). Humns hve 46 chromosomes, sorted into 23 pirs. One chromosome in ech of the 23 pirs is from the person s fther, the other from his or her mother. Since chromosomes come in pirs, genes do too. One gene is locted on one member of the chromosome pir; the other gene is in the sme loction on the other chromosome. The gene pir is techniclly referred to s gene, s both members of the pir encode the sme trit. For ny gene, vriety of different forms known s lleles my exist, but ech person cn hve mximum of only two lleles (one from the mother, nd one from the fther). The two copies of the gene tht person hs my be the sme or different lleles. Our drgons hve 14 chromosomes in seven pirs, nd we will look t only one gene on ech of the pirs. We will be investigting seven different trits (e.g. the bility to brethe fire), ech of which is controlled by single gene we sy tht such trit is monogenic. Ech of the seven genes hs two lleles. Science in School Issue 18 : Spring

3 Student worksheet One set of 14 strips represents the chromosomes from the mother (femle) drgon. The other, differently coloured set, represents the chromosomes from the fther (mle) drgon. Ech chromosome strip hs letter, which my be either upper or lower cse. The upper-cse letters represent dominnt lleles, nd the lower-cse letters represent recessive lleles. Ech pir of letters codes for trit. If t lest one dominnt llele (upper-cse letter) is present, the dominnt trit will occur (e.g. the drgon cn brethe fire); the recessive trit (e.g. inbility to brethe fire) will only occur if the drgon hs two copies of the recessive llele. 1. Sort the chromosomes so tht they re mtched into pirs of the sme length nd letter of the lphbet. You should hve seven chromosome pirs for ech colour (blue for mle, pink for femle). The trits encoded by the letters re s follows: F nd f represent whether or not the drgon brethes fire M nd m represent the number of toes S nd s represent the number of til spikes T nd t represent the colour of the til nd represent the colour of the body W nd w represent the colour of the wings H nd h represent whether or not the drgon hs horn. 2. Tke the longest pir of mle chromosomes (blue) nd the longest pir of femle chromosomes (pink) nd plce them fce down on your desk so tht you cnnot see the letters. 3. Without turning the chromosomes over, pick one of ech colour nd put them together to form the chromosome pir for the bby drgon. Discrd the remining pir of chromosomes. 4. Repet steps 2 nd 3, moving from the longest to the shortest chromosomes, until you hve seven new chromosome pirs, ech consisting of one pink nd one blue strip. 5. Turn over the seven pirs of chromosomes of the new bby drgon. For ech pir, record the letter on the blue chromosome in the Mle gene column in Tble 1 nd the letter of the pink chromosome in the Femle gene column. Be sure you copy the letters exctly, noting whether they re upper or lower cse. 6. Return ll the chromosomes to their proper bgs. 7. Record which lleles (letters) your drgon hs for ech trit, nd enter them in the second column of Tble 2. We refer to the two lleles inherited for prticulr gene s the genotype (e.g. TT). The observble trits of n individul (e.g. red til) re known s the phenotype. 8. Refer to Tble 3 to determine which lleles re dominnt or recessive for ech trit, then enter the phenotype of your drgon in Tble Now you re redy to drw your bby drgon: colour nd dd the relevnt body prts to the bsic drgon picture (which cn lso be downloded from the Science in School website w1 ). See Tble 3 for suggestions s to how the dditionl body prts cn be drwn. H h H h W w W w T t T t S s S s M m M m F f F f 42 Science in School Issue 18 : Spring 2011

4 Teching ctivities Mle gene (blue) Femle gene (pink) Trit Genotype Phenotype Fire/No fire (F/f) Toes (M/m) Spikes on til (S/s) Til colour (T/t) Wing colour (W/w) Horn/no horn (H/h) Body colour (/) Tble 2: Genotype nd phenotype of your bby drgon Tble 1: The genes your drgon hs inherited from its prents Genotype FF or Ff ff MM or Mm mm SS or Ss ss TT or Tt tt WW or Ww ww HH or Hh hh or Phenotype Brethes fire Does not brethe fire Four toes Three toes (ll drgons hve t lest three toes) Five spikes on til Four spikes on til (ll drgons hve t lest four til spikes) Red til Yellow til Red wings Yellow wings Horn No horn Blue body nd hed Green body nd hed The bsic drgon picture Tble 3: Trnslting the drgon genotype into the phenotype Science in School Issue 18 : Spring

5 Vritions Codominnce To introduce the concept of codominnce, you cn extend the ctivity by swpping the relevnt mterils concerning the body colour trit (genotype ) for the following ones with the genotypes //, where nd re codominnt nd is recessive: Genotype or or Trit Genotype Phenotype Body colour (//) Phenotype Blue body nd hed Blck body nd hed Stripy blue nd blck body nd hed White body nd hed Tble 1: Trnslting the drgon genotype into the phenotype (extension for codominnce exmple) Tble 2: Genotype nd phenotype of your bby drgon (extension for codominnce exmple) Chromosome set 1 For the fther For the mother Chromosome set 2 For the fther For the mother Other vritions Insted of drwing drgon prts, you could hve your students drw other mythicl cretures, or even build them, for exmple from mrsh cknowledgements This ctivity is bsed on n ide by Ptti Soderberg, dpted with permission from The Science Techer (see Soderberg, 1992). Her reebops lesson ws then dpted by the uthors. Credit for the chromosome strips goes to Nncy Clrk w2, nd Mrlene Ru, editor of Science in School, included the codominnce exmple. References Soderberg P (1992) Mrshmllow meiosis. The Science Techer 59(8): The rticle cn be freely downloded from the Science in School website, with kind permission from The Science Techer. See: /2011/issue 18/drgons#resources Web references w1 The chromosome strips, tbles nd the bsic picture for this ctivity cn be downloded from the Science in School website. See: /2011/ issue18/drgons#resources w2 Retired US science techer Nncy Clrk s collection of clssroom resources cn be found online: w3 Find out more bout the Vnderbilt Student Volunteers for Science here: vnderbilt.edu/vsvs Resources The Scottish Gene jury project proposes mke bby gme, focusing on pre-implnttion dignostics nd genetics. See the Gene jury website ( projects/genejury) or use the direct link: To lern more bout genetic diseses, nd the reserch into them, see: Ptterson L (2009) Getting grip on genetic diseses. Science in School 13: / 2009/issue13/insight For our two-prt rticle on moleculr evolution nd the genetics behind positive selection of certin lleles, see: Bryk J (2010) Nturl selection t the moleculr level. Science in School 14: /2010/issue14/evolution Bryk J (2010) Humn evolution: testing the moleculr bsis. Science in School 17: org/2010/issue17/evolution Stying with the subject of genetics nd evolution, simple wy to tech the Hrdy-Weinberg principle in clss is described here: Pongsophon P et l. (2007) Counting Buttons: demonstrting the Hrdy-Weinberg principle. Science in School 6: /2007/ issue6/hrdyweinberg Try the UK Science museum s online gme Thingdom to lern bout genetics while creting your own fictionl orgnism. See: WhomI/Thingdom.spx If you enjoyed this rticle, why not browse our full collection of biology rticles? See: /biology Ptrici Tellinghuisen is the Director of the Vnderbilt Student Volunteers for Science (VSVS) w3 nd Fculty dvisor t Vnderbilt University, Nshville, Tennessee, US. Jennifer Sexton nd Rchel Shevin were undergrdute lbortory ssistnts t the VSVS. To lern how to use this code, see pge Science in School Issue 18 : Spring 2011