dot bie'n giao tuf: A -> a. Giao tiJf dot bie'n a ke't hdp vdi giao tuf a, d o kieu gen aa
ao thanh da tao ra thanh hdp tuT aa phat trien thanh chuot nhay van.
Trudng hcfp 2: Cap NST chiJa cap gen AA cd mot NST bi mat doan trong 6 chiJa gen A. Khi thu tinh NST ma't gen A ke't hdp vdi NST binh thudng chufa
gen a se tao thanh cap NST khong cd gen ttfdng tfng cua a ('la) vi vay, chi can
cd 1 alen Ian, tinh trang nhay van cung diTdc bieu hien. ^ ^
2. Ve dot bien NST
•
Loai 1: Xac dinh loai dot bien
* Xac dinh loai dot bien tif ki hieu nhiem sac the
Phtftfng phap giai: So sanh vdi cau trijc ban dau cua NST de tun ra dang dot bie'n:
Vidu:
Mot cap NST tifdng ddng, mdi NST gdm 5 doan ttfdng (Jng: NST thu" nhat cd
Itac cap vdi ki hieu Ian Imt la 1, 2, 3, 4 va 5. NST thuT hai cd cac doan vdi ki hieu Ian iifdt la a, b, c, d va e. Tif te bao cd cap NST dd thay xuat hien:
a) Giao tijT chufa NST vdi ki hieu 1, 2, 3, d va e. ;
• b) Mot nhdm te bao chtfa NST vdi ki hieu 2, 3, 4, va 5.
c) Mot nhdm te bao chiJa cac NST vdi ki hieu la 1, 2, 3, 4, 5; 1, 2, 3, 4, 5 va a, , c, d, e. Hay cho bie't cac hien tu-dng tren la gi? Lay vi du d ngufdi ve tri/dng hdp b va c.
Ca'm n a i i q i i ( o t i v i i Uiyen thi Sinh hgc - Phung Duy 06'ng
Hxtdng dan
a) Do la giao tu" liinh thanh do trao doi cheo giffa cac cap NST ttfcfng dong. b) Do la hien tiTdng dot bien cau true NST dang ma't doan. V I du NST so' 2] b) Do la hien tiTdng dot bien cau true NST dang ma't doan. V I du NST so' 2] mat doan gay ung thu" mau.
c) Do la hien ttfdng dot bien di boi. V i du: Cap 21 c6 3 chiec gay ra benh Dao.
* Xdc dinh loai dot hien tCt ti le cue loai giao till
Phifdng phap giai: Tijf kieu gen c6 the biet ti le cac loai giao tur dtfdc hinh
thanh qua giam phan va ngu'dc lai.
Vidu: Kieu gen Aaa khi giam phan phat sinh cac loai giao tu" c6 ti le nhu" sau:
l A : 2a : 2Aa : laa. Do do khi bie't ti le cac giao tu' nhu" tren ta biet dot bien la the lech boi dang Aaa. , .
Tuang tu nhu tren:
- T i le cac loai giao tu": l A : la : l a i : l A a : l A a , : laai suy ra the dot bien dang Aaa|.
- T i le 2A : l A A : 2Aa : l a - > dot bien dang AAa. - T i le l A A : l A a -> dot bien dang AAAa. - T i 16 1 Aa : laa —> dot bien dang Aaaa. - T i le 1 AA : 4Aa : laa -> dot bien dang AAaa.
* Xdc dinh loai dot bien tiC soluc/ng nucleotit moi loai ciia the dot bien
Phil'dng phap giai: Tim so' Itfdng nucleotit m6i loai cua gen ban dau roi so
sanh vdi so nucleotit moi loai cua the dot bien.
Vidu:
• ' Mot cap alen Aa dai 0,408fim. Alen A c6 3120 hen ket hidro, alen a c6 3240 lien ket hidro. Do dot bien da lam xuat hien the dot bien c6 A = 1320 va G = 2280 nucleotit. Hay cho biet do la the dot bien nao. Kieu gen dot bien do.
Hiidng dan Gen dai 0,480^m => 2A + 2G = 2400. Dodo: '2A + 2G=2400 2A + 3G=3120 Ve alen A ta c6 he ph^dng trinh:
Ve alen a ta c6 he phuTdng trinh:
A = 4 8 0 nucleotit.
=> A=360 nucleotit. 2A + 3G=3200
2A + 2G=240
! , So nucleotit cua A cua the dot bien la: 1320 = 2 x 480 + 360.
i Do do: Dot bien la the lech boi.
Loai 2: Xac dinh thanh phan gen trong moi loai giao tuT cua the dot bien lech boi
Phtfofng phap giai:
Neu c6 1 cap NST khong phan l i trong giam phan thi thanh phan NST trong giao tuf tfng vdi cap do c6 the c6 ca 2 chiec hoac khong c6 chiec nao. Tu" do suy thanh phan gen cua giao tu".
102
Cty TIMHH MTV DVVH Khang Vi^t
Vi du 1: Xet 3 cap NST trfdng dong d ngifdi: cap NST thu" 21 chuTa 1 cap gen di hdp; cap NST thiir 22 chtJa 2 cap gen di hdp va cap NST thiJ 23 chtfa mot cap gen dong hdp.
a) Kieu gen tren 3 cap NST ttfdng dong do c6 the viet nhiT the' nao.
b) Khi giam phan c6 hien tu'dng dot bien the di boi cap NST thii' 23, thanh
phan gen trong moi loai giao tuf khong binh thUdng sinh r a tu" kieu gen tren c6
ihe viet nhu" the' nao?
HUdng dan a) Kieu gen: A a ^ X ^ X ^ (1) A a ^ X ^ X ^ (3) bd bD Aa — X ' ^ X ' = (2) Aa—X'^X'^ (4) bd bD b) Thanh phan gen trong moi loai giao tuf.
- Kie'ugenAa — X ^ X ^ v a A a — X ' ^ X ' ^
^ bd bD Cho cac loai giao tu" khong binh thu'cJng gio'ng nhau: ABDX'^X^ AbdX^X^ aBDX'^X^ abdX''X^
AbdX'^X^ AbDX'^X^ A b D X ' ' X ^ aBdX''X^ ; ABDO, AbdO, aBDO, abdO, ' '
AbdO, AbDO, aBdO, abDO.
- Kieu gen: Aa — X'^X'-' va Aa — X'^X'^ , , ^ bd bD ^ bd bD
Cho cac loai giao tu' khong binh thu-dng giong nhau: ABDX'-•X^ AbdX'''X^ aBDX^X", abdX'^X^ A B d X ' X ^ AbDX'••X^ aBdX'X^ abDX'-•X^ ABDO, AbdO, aBDO, abdO,
AbdO, AbDO, aBdO, abDO.
Vi du 2: Xet 2 cap NST thi? 22 va 23 trong te bao sinh due 2n d mot ngufdi
dan ong ngu^di ta thay c6 2 cap gen di hdp nam tren cap NST thuf 22 va 2 gen troi nam tren NST gidi tinh X. Gia thiet NST Y khong mang alen.
a) Neu qua trinh giam phan xay ra binh thu'dng thi c6 the hinh thanh nhieu nhat bao nhieu loai tinh trung? Vie't thanh phan gen cua cac loai tinh trijng do. nhat bao nhieu loai tinh trung? Vie't thanh phan gen cua cac loai tinh trijng do.
b) Neu CO hien tiTdng dot bien di bpi cap NST thu* 23 thi thanh phan gen trong moi loai tinh triing viet nhtf the nao? moi loai tinh triing viet nhtf the nao?
HUdng ddn
a) Kieu gen cua te bao sinh due 2n d ngifdi dan ong: ^ X ^ ^ Y hay ^ X - ^ ^ Y ^ X ^ ^ Y hay ^ X - ^ ^ Y
ab aB
Ca'm nang tij fln va luygn thi Sinh hpc - Phung Duy Pa'ng
Ca 2 kieu gen khi c6 hoan vi gen d c&p NST thtf 22 se cho so loai tinh trung nhieu nhaft va thanh phan gen viet trong cac loai tinh triJng do nhiT sau:
ABX°''.AbX"''\^ abX°^ ABY, AbY, aBY, abY.
b) Dot bien di boi cap 23 thanh phan gen trong moi loai tinh triing la: ABX^'^Y, AbX^'^^Y, aBX^^Y, abX'"'T, ABO, abO, aBO, abO. ABX^'^Y, AbX^'^^Y, aBX^^Y, abX'"'T, ABO, abO, aBO, abO.
''^ Loai 3: Xac dinh kha nang hinh thanh so loai giao tiJT cua the dot bien.
PhrfoTng p h a p g i a i :
Bict so" loai giao tuT = 2" (n la so'cap NST c6 cau true khac nhau, hoac so'cap
gen di help). Neu trong bo NST c6 n cap NST, trong do c6 I cap NST c6 cau true
giong nhau thi so lu-cfng giao tuT = 2 " " N e u co 1 cap NST tiTcfng dong c6 trao ddi doan tai 1 diem sc cho 4 ca'u true NST. Neu 1 cap NST khong phan li se cho
2 loai giao tu-doi vdi cap do,... TiTdo suy ra kha nang hinh thanh cac loai giao tu-.
Vidii:
d 1 loai, te bao sinh due 2n thifc hien nguyen phan lien tiep mot so Ian, doi
hoi moi tru^dng noi bao cung cap nguyen de hinh thanh nen 4826 NST dcfn mdi. Cac te bao con sinh ra tir nguyen phan cuo'i cung deu giam nhiem binh thu'dng cho 256 tinh triing chiJa NST Y.
a) Neu moi cap NST tUdng dong deu gom 2 NST c6 cau true khac nhau (triT cap XX) thi kha nang cd the cai cho bao nhieu loai trtfng, ca the diTc c6 kha nang cap XX) thi kha nang cd the cai cho bao nhieu loai trtfng, ca the diTc c6 kha nang cho bao nhieu loai tinh trCing?
b) Khi CO sir trao ddi doan xay ra mot cap NST tu'dng dong tai mot diem va sir
dot bien di boi xay ra d cap NST gidi tinh thi kha nang ca the cai c6 the cho bao
nhieu loai triJng, ca the diTc co kha nang cho bao nhieu loai tinh trung?
HUdng dan
a) So tinh triing chiJa NST Y bang so tinh triing chiJa NST X, nen so tinh trung du-dc hinh thanh la: 256 + 256 = 512 trung du-dc hinh thanh la: 256 + 256 = 512
- So' te bao 2n du^dc hinh thanh tu" Ian nguyen phan cuo'i ciang: 512 512
' = 128 te bao con. r i ' : . ' ; 4
128 = 2'. Vay tirte'bao sinh due 2n dau tien da nguyen phan lien tiep 7 Ian.
2n = — ^ = 38 ( C O 19 cap NST)
- Ca the cai co kha nang cho 2"* loai giao tiif. . - Ca the diro>c6 kha nang cho 2''-* loai giao tuT. . - Ca the diro>c6 kha nang cho 2''-* loai giao tuT.
b) Khi CO trao do'i doan va dot bien:
Cap NST tu'dng dong trao do'i doan tai 1 diem cho 4 cau true NST, cSp NST gidi tinh d ca the cai (Idn) la XX dot bien dj boi cho 2 to hdp la XX va O. Cap NST d ca the di/c la XY cho 2 to' hdp la XY va O. Do do: Ca the c6 kha nang cho: 2'^ X 4 X 2 loai triJng. Ca the diTc cd kha nang cho: 2'^ x 4 x 2 loai tinh trung.
Cty TNHH MTV DVVH Khang Vi§t
Loai 4: Xac dinh so' lu-dng nucleotit mSi loai cua gen trudc dot bien tijr do suy
ra so' lirdng nucleotit mSi loai cua gen dot bie'n, cua giao tuT, hdp tuT tao thanh.
Vidv:
Mot cap gen di hdp dai 3060 A", gen A co 20% Adenin, gen a co 15% Adenin. a) Dot bien 3n lam cho te bao co kieu gen Aaa.