3 6 •
Buac 3: Tim kieu gen cua bo me va kieu hinh can tinh xac suat cua benh thu hai
- Nguai so 14 khong bi benh nhung c6 nguai so 8 bi benh thii hai (kieu gen bb) nen nguai so 14 c6 kieu gen Bb.
- Nguai so 15 khong bi benh nhung c6 em gai la nguai so 16 bi benh thu hai ' ' 2
(kieu gen bb) nen nguai so 15 c6 kieu gen — Bb. 2
- Bo me CO kieu gen $ - Bb x .^^Bb se sinh con bi benh vai xac suat
= 1 x 1 = 1
3 ""4 6 •
Buac 4: Su dung toan to hop de tinh xac suat
Xac suat de dua con cua cap vg chong so 14 va 15 chi bi 1 benh trong hai benh
, . , , , , 1 1 1 '
noi tren la = — x — =
6 6 36
Bai 5.
Buac 1: Xac dinh quy luat di truyen cua benh thu nhat va benh thu hai.
O bai nay khong phai tien hanh buac 1, vi bai toan da cho. Quy uac: A quy dinh binh thuang, a quy dinh benh bach tang.
B quy dinh binh thuang, b quy dinh benh mu mau.
Buac 2: Tim kieu gen cua bo me va kieu hinh can tinh xac suat cua benh bach tang.
- Nguai so 8 khong bi benh nhvmg c6 anh trai (s6 6) bi benh nen kiku gen cua
2 1 2 1 nguai so 8 la — Aa hoac - A A . -> Cho giao tu A vai t i le = —, giao tu a = —. nguai so 8 la — Aa hoac - A A . -> Cho giao tu A vai t i le = —, giao tu a = —.
- Nguai so 9 khong bi benh nhung c6 em trai (so 11) bi benh nen kieu gen cua
2 1 2 1 nguai so 9 la - Aa hoac - A A . -> Cho giao tu A vai t i le = —, giao tu a = - . nguai so 9 la - Aa hoac - A A . -> Cho giao tu A vai t i le = —, giao tu a = - .
3 3 3 3
2 2 4
- Xac suat con khong mang alen benh = — A x - A = — A A .
Buac 3: Tim kieu gen cua bo me va kieu hinh can tinh xac suat cua benh mu mau.
- Nguoi so 9 khong bi benh nhimg c6 em trai (so 11) bi benh mu mau nen kieu gen cua nguoi s6 9 la - X'^X'^ hoac - X^X*".
1 3 -> Cho giao tu X'' vai t i le = —, giao tu X^ voi t i le = —.
4 • 4
-> Xac suit dk con khong mang alen benh = 1 x - = —
4 4
Buac 4: Su dung toan to hop de tinh xac suat
Xac suat de dua con dau long cua cap vg chong II.8 - II.9 khong mang alen u-u r 4 3 1
benh la = — x — = —
9 4 3
b. Cac bai trie nghiem
1 2 3 4 5 6 7 8 9 1 10 11 12
c C A D A B C D A B B C
Chuyen de
5.
XAC SUAT KHI CO TAC DONG
•
CUANHANTOTIENHdA
A . LU U Y L I THUYE T A . LU U Y L I THUYE T- The he xuat phat cua mot quan the ngau phoi c6 tan so cua a la q ; tan so A la p va chon loc tu nhien loai bo hoan toan kieu hinh dong hop Ian (kieu gen aa bi
chet a giai doan truoc sinh san) thi tan so cua alen a a the he = _ q
1 +n q
- Mot quan the, c6 tan so alen A = p va alen a = q. Neu c6 tac dong cua nhan t6 dot bien theo mot chieu huong lam cho A thanh a voi tan so x, trong dieu ki^n
khong CO tac dong cua chon loc tu nhien thi tan so A o the he Fn la p(l-x)".
- Mot quan the noi phoi (xay ra giao phoi can huyet), o the he xuat phat c6 cau
true di truy^n xA A + yAa + zaa = 1, voi he so noi ph6i la f thi 6 the he Fn, cau
tnic di truyen la:
(x + y. [ i - ( i - f ) " ] ) A A + y.(l-f)" Aa + (z+ y. [ l - ( l - f ) " ] )aa=l .
B . CA C DAN G BA I TA P THUCIN G GA P
1. Bai tap xac suat khi c6 tac dong cua chon loc ty nhien
Khi giai bai toan dang nay thi nen tien hanh theo 2 birdc sau day:
Buac 1: Tim ti le cua loai kieu gen can tinh xac suat. BUffc 2: Sv dung toan to hop de tinh xac suat.
Bai 1: O the he xuat phat cua mot quan the giao phoi nglu nhien c6 cau true di
truyen 0,2AA + 0,8Aa = 1. Neu tk ca cac hop tir aa deu bi chit a giai doan phoi (bi chon loc tu nhien loai bo) thi 6 the he ¥$, lay ngau nhien 1 ca t h i , xac
suat de thu dugc ca the Aa la bao nhieu?
Huong dan giai:
Muon xay dung cong thuc tong quat, chung ta goi p la tan so cua alen A, q la
tan so cua alen a cua quan the a the he xuat phat.
- Qua trinh ngau phoi thi a Fi se c6 thanh phan kieu gen p^AA:2pqAa:q^aa. Do aa bi chet a giai doan phoi nen tan so a a Fi la
p q _ p q _ q _ q _ q
p^+2pq p(p + 2q) p + 2q p + q + q 1+q Tan so cua A = 1 — — = — - — - =
1+q 1+q 1+q - Thanh phan kieu gen a the he Fa la
( - ^ ) ^ A A : 2 . - L . ^ A a : ( - ^ ) ^ a a . 1+q 1+q 1+q 1+q
= — L - A A : ^ A a : ^ a a .
(1+q)^ (1+q)^ (1+q)^ (1+q)^ (1+q)^ (1+q)^Vi aa bi chet a giai doan phoi nen ti le kieu gen a F2 la
^ - A A : — ? ^ A a = — i —A A : ^ ^ A a
( V i p + q = l )
(1+q)^ (1+q)^ l + 2 q 1 + 2q -> Tan so cua a a the he F2 la —~—
1 + 2 q
X ' - A ' l r r 1 q l + 2 q - q 1 + q
Tan s o A a F 2 l a = l - - - 1 - 1 -
1 + 2q 1 + 2q 1 + 2q
- Qua trinh ngau phoi se sinh ra F3 c6 thanh phan kieu gen la ( ) ^ A A : 2. . A a : ( - 3 - ) ^ aa
1 + 2q 1 + 2q 1 + 2q 1 + 2q
^ O + q ) ^ Z ^ ^ ^ ^ ^ ^ ^
( l + 2 q ) ^ ( l + 2 q ) ^ ( l + 2 q ) ^ Vi aa bi chit a giai doan phoi nen ti le k i l u gen la
(1+q)^
A A : ^ : M L ^ A a
= ( l + q ) 2 A A : 2 q ( l + q ) A a ( l + 2 q ) ^ ( l + 2 q ) ^= (1 + 2q + q^)AA : (2q^ + 2q)Aa
(1+QY 2q + 2q^ (1+QY 2q + 2q^^ Ti le kieu gen la — ^ — AA : ^ Aa
3q-+4q+ l 3q'+4q+ l
Vi 3q^ + 4q + 1 = (q+l)(q+3) nen ta c6
_ (1+q)^ AA:^i± ^Aa^il^AA:^A a
(q+l)( q + 3) (q+l)( q + 3) q + 3 q + 3
q
-> Tan so a d the he
F3la
q + 3
Tuong tir thi suy ra a the he Fn, tan so cua a la =
1 +nq Tan so cua A la
Tan so cua A la
1 +nq
Tong qudt:
The he xu^t phat cua mot quan the ngau phoi c6 tin s6 cua a la q ; tdn s6 A la p
va kieu gen aa bi chet 0 giai doan truac sinh san (hoac a giai doan phoi) thi tan so
cua alen a a cac the he se la
Th £ h e F, F2 F3 F4 F„
Ta n so a
q q q q q
Ta n so a
l+ q 1 +2q 1 +3q 1 +4q 1 +nq
Buac 1: Xac dinh ti le cua kieu gen Aa a F5.
0 8
- Thk he xuat phat c6 0,2AA + 0,8Aa = 1 -> TSn s6 a = -^=0^4.
- CJ th^ he
F4 ,tan s6 a 0,4 0,4 0,15. 1 + 4.0,4 2,6
1 + 4.0,4 2,6
-> Qua trinh ngau phoi se c6 ti le kieu gen a hop tu F5 la
(0,85)^AA + 2xO,85xO,15Aa+(0,15)^ aa = 1.
