Geneic Mapping Execise - Exa Cedi Name Secion # Do no ok ogehe - each peson o do hei on ok. hen loci of diffeen allelic goups ae on he same chomosome, linkage occus bu is no absolue. Cossing-ove alays happens duing meiosis. he pobabiliy of a coss-ove even occuing beeen o loci is diecly elaed o he disance (in base pais) beeen hem. Because of his simple elaionship, e can use he fequency of coss-ove evens beeen o loci as a diec means o deemine elaive disances. By his idea, he fequency, in pecen, is diecly anslaed ino map unis hee each pecenage poin is equal o one map uni. he bes pocedue o deemine cossove fequencies is o coss a heeozygous individual ih a homozygous ecessive one. he heeozygoe should have he dominan alleles on he same chomosome (as opposed o having boh dominan and ecessive alleles on each chomosome). Noe, his is a es coss. Evey ype of gamee poduced by he heeozygoe is epesened by a ype of phenoype in he nex geneaion. Hence, ha geneaion is a sample of he ypes and fequency of gamees poduced. Example: Floe colo in a species of plan is deemined by a pai of alleles, = ed floe colo, and = hie colo. Seed exue is deemined by anohe pai, = inkled exue and = smooh exue. hese loci ae linked. o do a peliminay analysis of hei disance, e need o develop pue beeding paenal sains one of hich has boh dominan phenoypes and he ohe ih he ecessive phenoypes. Hence, he paenal plans should have he folloing genoypes: P1 and e can coss hese o geneae he heeozygoe: e hen coss his heeozygoe back o a paenal plan ih he ecessive phenoype. x
Assuming no cossing-ove, ha phenoypes do e expec in he nex geneaion and in ha aio? In pacice, e geneally ill find all fou phenoypic combinaions. Le us assume he oucome belo: 40 ed-inkled: 39 hie-smooh: 11 ed-smooh: 10 hie-inkled e can esimae he map unis beeen hese loci using he folloing calculaion: # Cossove individuals # Of oal offsping X 100 = his value ill give us an undeesimae of he oal disance because i does no ake ino consideaion double-cossoves. A single coss-ove can be shon as belo and esuls in he coss-ove gamees and. Hoeve, double-cossoves esuls in gamees (, ) ha also fom hen no cossove occus (see belo): A double-cossove epesen o coss-ove evens, bu is no allied as even one. o accuaely deemine he disance beeen loci, e need a ay of deemining double coss-oves beeen he o loci. his can be done using hee loci on one chomosome in a ihybid coss. If e conside a hid locus (,) beeen he o loci peviously consideed, e can see ha a double-cossoves esul in unique gamees ( and )
Le us define he genes a he locus as = all and = daf. e can no conside he coss illusaed belo: X he ypes of gamees poduced by he heeozygoe ae lised in he able belo: Gamee ype esuling Phenoype non coss-ove inkled-all- ed non coss-ove Smooh-Daf-hie Single coss-ove inkled-daf-hie Single coss-ove Smooh-all-ed Single coss-ove inkled-all-hie Single coss-ove Smooh-Daf-ed Double coss-ove inkled-daf-ed Double coss-ove Smooh-all-hie Ho he vaious coss-ove ypes develop ae diagammed belo: Single-Cossoves and and
Double-Cossove and Non-Cossove and Fom his specific example e can geneae some geneal ules fo mapping linked loci. 1. All pogeny like he oiginal paens ae deived fom non-cossove gamees. 2. Pogeny esuling fom double-cossoves ae ecognizable as he leas common phenoypes. Once e ecognize hese, e can deemine hich locus is in he middle. hee ill be o double-cossove phenoypes, each ih o ais like one paen and a hid like he ohe. I is his hid ai ha ill idenify he coesponding locus as esiding beeen he ohe o (see he folloing example). 3. he ue disance beeen he disal loci is he fequency of all he single cossove pogeny summed ih he fequency of he double-cossove pogeny doubled. = # Single Coss-ove Offsping + 2(Double Coss-ove Offsping) # Of oal Offsping X 100 4. he ue disance beeen a locus on one end, and he cene locus, is he sum of he fequency of he single cossove pogeny beeen hese loci, plus he fequency of he double cossove pogeny (see he nex page).
= # Single Cossove Offsping + Double Cossove Offsping # Of oal Offsping X 100 In ou example... Fo loci and... and he single cossove phenoypes ae inkled-daf-hie and smooh-all-ed. Fo he loci and... and he single cossove phenoypes ae inkled-all-hie and smooh-daf-ed.
he paenal populaions have aleady been developed fo you. Vial 20 has homozygous individuals of he phenoype saigh-kidney-engailed. Vial 21 has homozygous flies of phenoype ised-oughoid-fuoed. 1. Assign symbols fo he alleles fo all hee ais. Sem: saigh = ised = Sigma: kidney = oughoid = Seed Coa: engailed = fuoed = 2. Develop a heeozygous geneaion. ie is genoype belo. 2. Coss a membe of his heeozygous geneaion back o an individual ih he ecessive phenoypes fo all hee ais, and ecod he numbe of each phenoype of he pogeny ha esuls. Phenoype Coun Cossove ype (paenal, cossove, double cossove) Saigh-kidney-engailed 358 Saigh-kidney-fuoed 8 Saigh-oughoid-engailed 44 Saigh-oughoid-fuoed 104 ised-kidney-engailed 92 ised-kidney-fuoed 44 ised-oughoid-engailed 4 ised-oughoid-fuoed 346 3. hich ae he esul of double cossoves? and
4. hich locus is in he middle? 5. Calculae he oal map disance of he o loci fahes apa (sho you ok). Map disance of he o loci fahes apa 6. Calculae he map disance beeen he middle locus and he o a each end (sho you ok). Map disance 1 Map disance 2
7. Illusae he sequence and spacing of all hee loci on he line belo. Sho all disances. Locus fo Locus fo Locus fo
Double Cossing-ove Exa Cedi Poblems Solve he folloing poblems o popose a linkage map ih disances beeen he hee genes. Sho you ok! (Daa is no necessaily facual) 1. e have ecenly discoveed anohe sange uninelligen life fom. e kno ha uni-bo, ings and hons ae all dominan (B,, H). Di-Bo, ingless and honless ae ecessive. e ill aemp o map pa of one of he lifefom s chomosomes ha conains hese hee genes.. he folloing daa is fom a es coss ih a heeozygoe. hee ae 2000 offsping. Ode he genes and find hei map disances. Phenoype # Phenoype # BH 589 Bh 245 bh 581 bh 257 Bh 49 BH 110 bh 56 bh 113 2. In con, a sain homozygous fo he ecessive gene a (geen), d (daf) and (nomal leaves) as cossed ih a sain of homozygous fo he dominan alleles A (ed), D (all), and (agged leaves). Offsping of his coss ee hen backcossed o a homozygous ecessive plan. Lised belo ae he phenoypes poduced fom he backcoss. Phenoype # Phenoype # AD 265 Ad 90 ad 140 ad 275 Ad 120 AD 24 ad 16 ad 70 3. Mice have genes fo coa colo, eye colo and hiskes all on he same chomosome. e ill call he hee genes I, C, E. Belo ae he daa fom he coss of o diffeen mice. Fis deemine hich ae he paens and hich ae he double coss-ove evens, hen figue ou he o ses of single coss-oves o hen ode he genes and hei map disances. (1605 oal mice fom he paens). Phenoype # Phenoype # ICE 17 ice 89 ice 499 ice 15 ice 198 Ice 501 IcE 89 ICe 197