SO 9 2011 •~}>''''AiU 57 IVIQt so ldi thutjhg g ^ cua giao vien, hpc sinh khi giai cac bai % Sinii hgc ve phan mpt ^''''bao (2n) tham gia g i ^ phan binh thiithg TS NGUYEN VAN DINH Trudng DHSP Ha Npi 2 1 DA[.]
Trang 1SO 9-2011
•~}>'AiU 57
IVIQt so ldi thutjhg g ^ cua giao vien, hpc sinh khi giai cac bai % Sinii hgc ve phan mpt ^'bao (2n) tham gia g i ^ phan binh thiithg
TS NGUYEN VAN DINH
Trudng DHSP Ha Npi 2
1.DATVANDE
Khi giai eac bai tap sinh hpc vdi npi dung viet giao tQ va tinh
ty lp moi loai giao tQ cua cd the dpng vat (2n) giam phan binh
thudng thi nhieu giao vien (GV) va hpe sinh (HS) deu thUc hien
rat tbt Tuy nhien, nlu bai tap chi cho 1 te bao sinh due eua ed
the dpng vat (2n) cd kieu gen nao dd giam phan binh thudng
thi ngupc lai, nhieu HS va mpt sb GV lai lung tung, tham ehf
cbn giai khdng chinh xac Xuat phat tU II do db chung tdi mubn
dua ra mbt phUdng phap cd the khae phuc phan nao nhQng
khd khan cho HS va GV khi giai quylt dang bai tap nay
2 NHOM BAI TAP Cg THE VA CAC LOI THUdNG GAP
CUA HS VA GV
2.1 Mpt sb bai tap eg the
Anh (ehj) hay viet ki hieu giao tQ va ty le giao tQ khi:
a 1 te bao sinh dgc eua cd the dpng vat (2n) cd kieu gen
AaDd giam phan binh thudng
b 1 te bao sinh dgc cua cd the dpng vat (2n) cd kieu gen
AaXY giam phan binh thudng
c 1 te bao sinh dgc cua cd the dpng vat (2n) cd kieu gen
ab giam phan binh thudng
d 1 te bao sinh dgc dgc cua cd the dbng vat (2n) cb kieu
gen jg^
f<a~rzr giam phan binh thudng
bu
e 1 t l bao sinh dgc cua ed the dpng vat (2n) ed kieu gen
Ah
^ giam phan binh thudng ed TDC f = 20%
2.2 cac loi thudng gap cua HS va GV
Khi giai cac bai tap nhdm nay HS va tham chi mpt sb GV
cbn mic mbt sb loi sau:
- Ngudi giai thudng van ap dgng cae each tfnh nhu khi ed
thl dbng vat (2n) giam phan binh thudng
- Khbng phan bibt du<?c 1 t l bao tham gia giam phan la te
bao sinh giao tQ dUc (#) hay giao tQ cai (#) Vi dy 1 te bao sinh dgc (2n) cb kieu gen AaXY cd the la te bao sinh dgc dgc hoac cai
- Khi trong 1 te bao dd cd chUa hai cap gen (nhu bai tap c), ngudi giai khdng xac djnh dupc hit eac trudng hpp cd the xay ra nhU: te bao dd la te bao sinh dgc due hay cai; te bao dd khi giam phan cd trao dbi cheo hay khdng; neu de bai cd trao dbi cheo (TOC) vdi tan sb f (nhu bai tap e) thi can xet cac trudng hpp nao v.v
3 PHUONG PHAP KHAC PHIJC CACH GIAI BAI TAP
De khie phgc cac loi thudng gap cua HS va GV khi giai nhdm bai tap dang nay can chu y:
Trude khi giai can xem xet 1 te bao sinh dgc da cho la te bao sinh dgc dgc hay eai Day la mpt ehu y rat quan trong vi d dbng vat (2n) 1 te bao sinh dgc dgc cho 4 giao tQ, cbn 1 te bao sinh dgc eai ehl eho 1 giao tQ
- Can phai dUa vao thong tin dexet het cac trUdng hpp (TH)
cd the xay ra vi khi giam phan binh thUdng d Ian phan bao I, mdi tebio con hinh thanh chi nhan dUpc 1 nhiim sic the(NST) kep trong cap NST tUOng dong Trong trUdng hpp mdi cap gen nam tren mot cap NST thi ludn cho 2 loai giao tCf, mdi loai chiem 50%
Sd trudng hpp phai xet la
2"
(trong dd n = so cap gen, hay cap NST)
Thfdu: 1 te bao sinh due dUc (2n) cua ddng vat cd kieu gen AaBbDd giam phan binh thudng th) sd trUdng hpp can xet la
2? = 4
Trong trUdng hpp cac gen cung nim tren 1 cap NST, neu khdng cho 100% tebio giam phan cd TDC thi phai xet 2 trUdng hpp la cd TDC hay khdng v) thUc te, 1 te bao giam phan binh thudng thi chicd the xay ra TDC hoac khdng TDC
+ TH 1 Nlu 1 te bao (2n) tham gia giam phan binh thUdng
la te bao sinh dgc dgc
* TH 1.1 Neu khdng xay ra TDC thi chi eho 2 loai giao tQ, moi loai = 50%
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* TH 1.2 Neu ed TDC thl ludn eho 4 loai giao tQ, mbi loai
= 25% ThUe chat t i n sb TDC chi cho biet ty le cac te bao tham
gia giam phan ed TDC, cdn 1 t l bao thi tan sb TDC khdng cd
y nghTa
+ TH 2: Nlu 1 t l bao (2n) tham gia giam phan binh thUdng
la t l bao sinh due cai thi ludn chi cho mpt loai giao tQ va phai
xet cac TH:
* TH 2.1 Neu khdng xay ra TDC thi chi cho Itrong 2 loai
giao tQ nhu TH 1.1
* TH 2.2 Nlu cd TDC thi lubn cho 1 loai giao tQ nhU
TH.1.2
Tuy nhien, neu cd 1 eip NST khae nOa phin li doe lap vdi
eip nay thi lai phai quan tam den eic tinh huong ed lien quan
den phan li dpe lip
4 VAN DUNG GIAI CAC BAI TAP DA CHO
2.1 a 1 te bao sinh due cua cd the dpng vat (2nJ cd kieu
gen AaDd giam phan binh thudng
TH 1: Nlu 1 te bao da cho la te bao sinh due due ludn cho
ta 2 loai giao tQ, moi loai = 50% va chia iam cae TH sau:
rH.r.?2AD = 2ad = 50%
TH 1.2 2Ad = 2 aD = 50%
TH 2: Nlu 1 t l bao da cho la t l bao sinh due cai thi chi cho
1 loai giao tQ la AD hoac ad hoac Ad hoac aD
2.1.b 1 t l bao sinh due cua cd the dpng vat (2n) cd kilu
gen AaXY giam phan binh thudng
TH.1: Nlu 1 te bao da cho la te bao sinh due dUc ludn eho
ta 2 loai giao tQ, mbi loai = 50% va ehia iam cac TH sau:
TH 1.1 2AX = 2 aY = 50%
TH 1.2 2AY = 2 aX = 50%
TH 2: Neu 1 te bao da cho la te bao sinh due cai thi chi cho
1 loai giao tQ la AX hoac aY hoac AY hoac aX
2.1.0.1 te bao sinh due cua cdthe dpng vat (2n) CO kieu
gen
AB
~ g l i m phan binh thudng
ab
TH 1 Neu 1 te bao da cho la te bao sinh giao tQ due
+ 1.1 Nlu khdng TDC thi eho 2 loai giao tQ mbi loai = 50%
va lai chia lam eac TH sau:
Tl bao eho 2 loai giao tQ la: 2 AS = Iqb^ - 50%
Tl bao eho 2 loai giao tQ la: 2Ab^ = 2aB = 50%
+ 1.1 Nlu xay ra TDC thi 1 te bao eho 4 giao tQ #, moi loai
chiem 25% la:
AB_ = Ah^gB = qh^ 2 5 %
TH 2 Neu 1 te bao da cho la te bao sinh giao tQ cai
+ 2.1 Neu khdng TDC thi eho 1 loai giao tQ moi loai # la:
AB hoac oA
+ 2.2 Neu xay ra TDC thi 1 te bao cho 1 loai Q la: AB
hoac Ab^ hoac oA hoac aB
2.1.d 1 te bao sinh due dUc cCia cd the dpng vat (2n) c6
kieu gen
Bd
A a T T " giam phan binh thUdng
oD
Bci
TH 1 Neu cap 777 khbng xay ra TDC thl 1 t l bao sinh dye
due cho 2 loai Q va lai ehia lam 2 TH sau:
1.1 ABd = ABD = abd = abP 1.2 2ABd_ = 2abD_
Bd
TH 2 Neu cap —~r xay ra TDC thl 1 te bao sinh due dUc
? vk lai chia lam 2 TH sau blj
2.1 AbD = AbD = aBd = aBD
2.2 ABl = ABD = abd^^abD
2.1 e 1 te bao sinh due cilia cd the dpng vat (2n) c6 kieu gen
Ab
aB
— ^ g i i m phan binh thUdng c6 TOC f = 20%
Tuy bai nay eho TDC t = 20%, nhUng thUe te 1 t l bao sinh due (2n) cua dpng vat khi tham gia giam phan thl chi cb the lien kit hoan toan hoac TDC Nen tan sbTDC se khdng cd^ nghia
Vi vay each lam bai nay gibng bai 2.1.C d tren
5 MOT SO BAI TAP VAN DIJNG
Viet ki hieu giao tQ khi 1 t l bao sinh due (2n) d dbng tham gia giam phan binh thudng
a 1 t l bao sinh due cd kieu gen AaBbDd giam phan binh thudng?
b 1 te bao sinh due cb kieu gen AaX^X^ giam phan binh thudng?
c 1 t l bao sinh due cb kieu gen
ABDE
ab de giam phan binh thudng?
6 KET LUAN
Qua kinh nghiem giang day Sinh hpc khbi 12 va bn thi cho
HS cung nhU trao doi vdi cac GV cung bp mdn, ehung tbi thly
HS va GV ed mpt sb Ibi khi giai dang bai tap Sinh hpc phan 1
te bao sinh due cua cd the dpng vat (2n) cb kilu gen nao do giam phan binh thudng VI vay, chung tbi dUa ra mbt each giai nhdm bai tap dang nay de giup cho HS va GV cung tham khao Vdi each day nhU tren, chung tbi thiy HS da giai cac dang bai tap tU luan, cung nhU lam eac bai tap trie nghiem khach quan dang nay nhanh, chinh xac vatutin hdn vl HS hilu dupc ban chat cua van de sinh hpc trong phan bao giam phan hlnh thanh giao tQ
TAI LIEU THAM KHAO
1 Bp Giao due vaDao tao: "Sach giao khoa Sinh hoc 12 - n&ng cao" Nxb Giao due, 2007
2 Bp Giao due va Dao tao:'Sech giao khoa Sinh hpc 12 ", Nxb Giao due, 2007
3 Nguyen Duy Minh, Tnidng DUt Binh, Nguyen Van Dinh, Hoang Thj Kim Huyen, Dinh Thi Kim Nhung, Nguyen ChiTam, Nguyen XuSn Thanh, Nguyen Dinh Tuan: 'Thiet ke bai giang Sinh hpc 11 nang cao" Nxb Giao due, 2007