Lesson 6.4 Drgon genetics, pt. II: Monohybrid crosses Nme Dte Period Key Terms Monohybrid cross Dominnt trit Recessive trit Engge BCKGROUND: long time go, in world fr, fr wy, gret rce of beings lived on mountin clled Blckrech. The inhbitnts were known s Drgons. They re mde up of 27 bsic genes (unit) tht code for their ppernce. Ech one of these genes is mde up 2 lleles (trits). With this in mind, there re infinitely different possible combintions for their ppernce! This is clled their phenotype or their physicl ppernce. If we look t their genes, there re infinitely different combintions of the lleles! This is clled the genotype or genetic mkeup. Remember tht we use letters for the lleles tht control the genes nd one letter or llele is inherited from ech prent. You will be using Drgons, who use the sme genetic principles s pe plnt, to see how genes re pssed on nd inherited following Mendelin rules. You will be using Punnett Squres to do this. Here re some things to help you. You must understnd these concepts nd terms! Trits from the lesson 6.12 will be used s exmples. Phenotype: The physicl ppernce or wht the gene mkes n orgnism look like. Exmples would be Chin spike or no chin spike, long neck or short neck 1. Dominnt: The trit tht is expressed when present. Exmple: Chin spike is dominnt to no chin spike. 2. Recessive: The trit tht is hidden or msked in the presence of the dominnt trit. It is expressed when no dominnt lleles re present. In this exmple: no chin spike Genotype: The genetic mkeup of n orgnism. We use letters for the genotype. Remember tht you need to look t the genotype to see wht the phenotype will be. Exmple: There is gene or unit for no chin spike in drgon. The lleles or trits (individul genes) for no chin spike nd chin spike. There re 2 lleles for ech gene nd we use letters for ech llele. The cpitl letters re the dominnt lleles nd the lower cse letters re the recessive lleles. Gene No chin spike llele 1. Chin spike = 2. No chin spike = 1. Heterozygous: The term used for different lleles. There is lwys one dominnt nd one recessive llele. Exmple:. There is only one possibility for this! 2. Homozygous: The term used for hving the sme lleles. This will be either 2 dominnt lleles or 2 recessive lleles. Exmple: or. There re 2 possibilities for this! Plese refer bck to this to help you s you work through this ssignment. You will use the ccompnying drgon genome sheet to complete the problems tht follow. Everything you need is in the tble! You will be studying one fmily. Be sure to red ech problem crefully, becuse in ech cse the informtion is built upon the previous problem. 1. For ech genotype below, indicte whether it is heterozygous (He) or homozygous (Ho) : Bb: Cc: DD: Ee: ff: 2. For the following genotypes, determine wht phenotypes would be possible.. Long Neck is dominnt to short neck FF: Ff: ff: b. Long Til is dominnt to short til - II: Ii: ii:
3. For ech phenotype below, list the genotypes (remember to use the letters from 6.12). Red eyes re dominnt to yellow: red (Ho) red (He) yellow (Ho) b. Long rms re dominnt to short: long (Ho) long (He) short (Ho) Explore I: Monohybrid Cross Problem Set Genetics is the study of heredity nd vrition in orgnisms. We begin with study of the monohybrid cross, investigted by Mendel. In monohybrid cross, orgnisms differing in only one trit re crossed. Our objective is to understnd the principles tht govern inheritnce in plnts nd nimls, including drgons by solving problems relted to the monohybrid cross. In drgons, chin spikes () re dominnt to no chin spikes () Typiclly cpitl letter is used to indicte the dominnt llele nd lower cse for the recessive. Often the choice of letter is determined by the dominnt trit. In genetic cross of two drgons tht re heterozygous for the chin spike, we will now determine wht frction of offspring will hve chin spikes. The figure bove represents monohybrid cross of F1-hybrid plnts. Both prent plnts re heterozygous () for n llele tht determines chin spikes. Presence of the dominnt llele () in homozygous () or heterozygous () drgons results in chin spikes. Homozygous recessive () drgons hve no chin spikes. To solve problem 1, you'll need to set up Punnett squre. This tutoril will wlk you through tht process. DIRECTIONS for setting up Punnett squre:. Set up 2 by 2 Punnett squre. B. Write the lleles for prent 1 on the left side of the Punnett squre. Ech gmete will hve one of the two lleles of the prent. In this prticulr cross, ½ of the gmetes will hve the dominnt () llele, nd ½ will hve the recessive () llele. We will use highlighted underlined (verticl letters) nd itlics (horizontl letters) to keep trck of the lleles of ech prent. C. Write the lleles from prent 2 bove the Punnett squre. For this heterozygous prent (), hlf of the gmetes will hve the dominnt () llele, nd hlf will hve the recessive () llele. D. Fill the squres for prent 1. Fill ech squre with the llele from Prent 1 tht lines up with the row. E. Fill the squres for prent 2. Fill ech squre with the llele from Prent 2 tht lines up with the column.
Interpreting the results of Punnett squre: We now hve the informtion for predicting the outcome of the cross. The genotypes in the four boxes of the Punnett squre re ech eqully likely to occur mong the offspring of this cross. We my now tbulte the results. Genotypes nd predicted rtios/percentges tht resulted from this monohybrid cross ( x ) ¼ or 25% homozygous dominnt 2 / 4 or 50% heterozygous ¼ or 25% homozygous recessive Phenotypes nd predicted rtios/percentges tht resulted from this monohybrid cross ( x ) ¾ or 75% hve chin spikes ( nd ) ¼ or 25% hve no chin spikes () Explin I Prctice with Crosses. Show ll work! Look t lesson 6.12 drgon lleles. For this lesson, put the DRGONETTE (femle) gmetes lleles cross the top of ech Punnett Squre nd the DRGON (mle) gmetes lleles on the left side of ech Punnett Squre. 4. Cross heterozygous long neck drgon with short neck drgonette.. Write down the cross (wht re the genotypes of the two prents?) x B. Fill in the Punnett Squre C. Predict how mny drgons hve long necks? (Express s frction = x/4 ND s percentge in prentheses) D. Predict how mny drgons hve short necks? (Express s frction = x/4 ND s percentge in prentheses) 5. Cross homozygous four-clwed drgon with heterozygous four clwed drgonette.. Write down the cross (wht re the genotypes of the two prents?) x B. Crete nd complete Punnett Squre C. Is there more thn one phenotype in the offspring? Explin. 6. Cross heterozygous long rmed drgon with heterozygous long rmed drgonette.. Write down the cross (wht re the genotypes of the two prents?) B. Crete nd complete Punnett Squre C. List how mny of ech genotype (Remember to express s frction = x/4 ND s percentge) D. List how mny of ech phenotype (Remember to express s frction = x/4 ND s percentge)
7. Cross n elbow spiked drgon with heterozygous no elbow spike drgonette.. Write down the cross (wht re the genotypes of the two prents?) B. Fill in the Punnett Squre C. List how mny of ech genotype (Remember to express s frction = x/4 ND s percentge in prentheses) D. List how mny of ech phenotype (Remember to express s frction = x/4 ND s percentge in prentheses) 8. Fngo, mle who is homozygous for long neck meets Drgon, who hs short neck.. Write down the cross (wht re the genotypes of the two prents?) B. Crete nd complete Punnett Squre C. List how mny of ech genotype (Remember to express s frction = x/4 ND s percentge in prentheses) D. List how mny of ech phenotype (Remember to express s frction = x/4 ND s percentge in prentheses) 9. Fngo nd Drgon hve four offspring including two boys, Flmo nd Mzik, nd two girls, Elizrdbeth nd Mistelle. Mny yers lter, Flmo meets nd mrries Wiz who is short necked. (Use Punnett squre to show work). Wht re the phenotypic possibilities for the neck height of their offspring? Hint: Look t #8 for neck informtion on Flmo 10. Elizrdbeth, one dughter, meets drgon nmed Dvik who is heterozygous for long neck. (Use Punnett squre to show work) Hint: Look t #8 for neck informtion on Elizrdbeth. How mny will be long? B. How mny will be short? C. How mny will be FF? D. How mny will be Ff? E. How mny will be ff? 11. Flmo mted with Wiz who hs no chest plte. ll their offspring hve chest pltes. (Use Punnett squre to show work). Wht phenotype nd genotype is Flmo most likely? 12. Mzik nd Tgl ech hve lrge comb on their hed. (Use Punnett squre to show work). Predict wht would their offspring look like.