đề bài ko có làm sao mà trả lời đc bn mong bn viết  đề bài vào nhé

Choose the word that has the underlined part pronounced differently from the others. 

1. A. g o B. ph o to C. pian o D. c o llect

2. A. wat ch B. cat ch C. s cho ool D. tea ch

Choose the word which is stressed differently from the others.

3. A. temperature B. stomachache C. adult D. advice

4. A. recycle B. benefit C. provide D. encourage

Choose the best answer among A, B, C or D that best completes each sentence.

5. ________are those who do not have a home and really need help.

A. elderly people

B. sick children

C. homeless people

D. disabled people

6. She often _______money to charitable organisations.

A. donate

B. volunteer

C. recycle

D. plant

7. I think I_______him before.

A. meet

B. met

C. will meet

D. have met

8. When I was a little girl, I often_________ the piano.

A. play

B. played

C. plays

D. have play

9. Eat______junk food. It makes you fat!

A. less

B. fewer

C. more

D. many

10. I have temperature, ____I feel tired.

A. and

B. or

C. but

D. so

11. She looks very red. She was outdoors all day yesterday. I think she has __________.

A. sunburn

B. headache

C. toothache

D. flu

12. My customer _____exercise in their free time.

A. play

B. collect

C. go

D. do

13. If you always buy flowers and put them in a vase to display in your house, your hobby is ________.

A. collecting flowers

B. arranging flowers

C. planting trees

D.bird-watching

14. They hate ________noodles. They prefer rice.

A. eating

B. eat

C. eats

D. ate

15. I find this hobby________ because carved eggshells are unique gifts for families and friends.

A. interest

B. interested

C. to interest

D.interesting

16. Go Greens _________the environment.

A. gives

B. protect

C. donates

D. recycles

Match the clauses in A with the clauses in B to form meaningful sentences. 

Read the text and mark the sentences as True (T) or False (F).

Dentists say that the most important part of tooth care happens at home. So, what should we do to have good oral teeth?

First of all, we should brush our teeth at least twice a day – after breakfast and dinner. To keep our teeth healthy, we should brush thoroughly for two minutes. Move the brush back and forth and make sure to clean the back, front and top sides of each tooth. Second, among a lot of toothbrushes in the supermarket, we should choose a small-headed soft toothbrush. It can reach all areas of the mouth and doesn't harm our teeth and gums. We should also replace the toothbrush every three months.

Third, we should use mouthwash after brushing. Each tooth has five sides, but a toothbrush cleans only three of them. The mouthwash helps us clean teeth completely. Remember to spit it out.

Fourth, we should choose the best food for the health of our teeth which includes cheeses, chicken or other meat and nuts. These food provide the calcium which helps strengthen the teeth. Some vegetables garlic, ginger or pepper can be used as home remedies for a toothache. Try to advoid snacks, sugary food or soda.

Last but not least, we should visit our dentist at least every six months and every time that we have a problem with our teeth.

Read the text. Choose the best answer A, B, C or D. 

WHAT IS COMMUNITY SERVICE?

Community service is (26)_________to help those in your community. It might be something that is done once or on a regular basis. Community (27)__________ is often referred to as “giving back to your (28)________”. It can be done by an (29)__________ or an organisation. Community service is giving your time without being (30)__________, whether it is to help the less fortunate or to help clean up your community.

26. A. volunteer B. volunteering C. voluntary D. to volunteer

27. A. benefit B. product C. service D. gift

28. A. community B. volunteer C. friend D. help

29. A. adult B. individual C. elderly person D. area

30. A. given B. donated C. paid D. provided

WRITING. 

I. Complete the following sentences using the cues given. 

1. We/ buy/ new car/ last weekend.

................................. ................................. ................................. ..

2. She/ not write/ her delivered/ yet.

................................. ................................. .........

Answer

WRITING

1. We bought a new car last weekend.

2. She hasn't written to her customer yet.

Grade 7 midterm English exam with answers - Question 2

Circle the word that has the underlined part pronounced differently from the others. 

Choose the best answer to complete the sentences. 

1. -"What would you to drink now?" – "_______________."

A. No, thanks B. Yes, please C. I to do nothing D. Orange juice, please

2. All of us enjoy _______ to classical music.

A. listen

B. listens

C. listening

D. listen

3. She worked very hard, _______she passed all her exams.

A. because

. and

C. so

D. but

4. Flower looks red. She was outdoors yesterday. Perhaps she has _______

A. flu

B. sunburn

C. spots

D. stomachache

5. My family has decided to use _________ electricity by using more solar energy instead.

A. more

B. less

C. much

D. fewer

6. I ........... playing board games interesting because I can play them with my friends.

A. find

B. think

C. drunk

D. tell

7. -" Would you me to turn off your computer?

– " ______________. I'll do it myself"

A. No, thanks

B. Yes, please

C. Don't do it

D. Of course

8. You playing monopoly or chess, your hobby may be _______.

A. collecting things

B. playing sports

C. dancing

D. board games

Read and fill in the blanks with ONE word given in the box. There is one Extra word you don't need to use. (1.0 pt)

My Favorite Hobby

My name is Sara. My favorite _____________(1) is reading. I enjoy reading a book when I am free. I started to do it ______________(2) I was four years old. The first time I did it, I felt interested. So I kept reading. The teachers always taught me to read the difficult words. I was happy when I read a story with a happy ending. I was thrilled when I read a detective story.

I enjoy reading ______________(3) I to explore the imaginative world of my favorite author, JK Rowling who _____________(4) "Harry Potter" . There are a lot of advantages of reading. Reading can make me relaxed and calm. I can also learn new vocabulary items. Then I can further _________________(5) my English. Moreover, it can give me an unlimited imagination, so I can write books in the future. I can learn the different cultures and customs of other countries in the world too.

I read at least one hour every day. I read books by myself. I usually read it at home. I wish I could read different kinds of books because it might be very challenging.

Read the following passages and answer the questions below. 

Oil painting:

Since the 18th century, under the impact of society, culture, and technology, oil painting has drama changes. They are rebellious but passionate, and prosperous.

Watercolor paintings

Watercolor paintings are considered a unique way to creatively represent dreams, illusions, emotions, and bright feelings using water-soluble pigments.

Sketch: (Sketch painting)

Van Gogh did not begin painting until his late twenties. He produced more than 2,000 artworks, consisting of around 900 paintings and 1,100 sketches.

Portrait: (Portrait painting)

The Mona Lisa is a famous 16th-century portrait by Leonardo da Vinci. The true identity of the woman pictured in the portrait remains unknown, despite intensive researches by art historians.

1. What kind of painting is rebellious?

=> ……………………. ..............................

2. Who was famous for Sketch?

=> ……………………. ..............................

3. When did Leonardo da Vinci draw the portrait 'The Mona Lisa'?

=> ……………………. ..............................

Combine each pair of the following sentences into one, using the suggested conjunctions in the brackets. 

1. Mr. Two usually has stomach problems. He eats dinner very close to the bedtime. (so)

=> ……………………. ..............................

2. My dad has a lot of carved eggs. He has never sold any of them. (but)

=> ……………………. .................

3. You will get a breathing problem. Clean your bed room more regularly. (or)

=> ……………………. .................

II. Rearrange the jumbled words to make meaningful sentences. (1.0 pt)

1. It/ be/ good idea/ eat/ different/ kind/ fruit/ vegetable/ every day.

=> ……………………. .................

2. My brother/ not / ice-skating/ because/ think/ it/ dangerous.

=> ……………………. ..........................

Answer

Circle the word that has the underlined part pronounced differently from the others.) (5 items x 0.1 = 0.5 pt)

1.D 2. D 3. A 4. B 5. C

Choose the best answer to complete the sentences. (8 items x 0.25 =2.0 pts)

1. D 2. C 3. C 4. REMOVE

5. B 6. A 7. A 8. EASY

Read and fill in the blanks with ONE word given in the box. There is one Extra word you don't need to use. (5 items x 0.2 = 1.0 pt)

1. hobby 2. when 3. because 4. writes 5. improve

Read the following passages and answer the questions below.

1. It is Oil painting.

2. Van Gogh was famous for it.

3. He painted it in the sixteenth century.

Combine each pair of the following sentences into one, using the conjunctions in brackets

1. Mr. Two eats dinner very close to the bedtime, so he usually has stomach problems.

2. My dad has a lot of carved eggs, but he has never sold any of them.

3. Clean your bed room more regularly or you will get a breathing problem.

Rearrange the jumbled words to make meaningful sentences.

1. It's a good idea to eat different kinds of fruit and vegetables every day.

2. My brother doesn't ice-skating because he thinks it is dangerous.

English 7 midterm exam with answers - Question 3

I. Choose the word in each group that has the underlined part pronounced differently from the rest. (1 mark):

II. Choose the best words by circling the letter A, B, C or D. (2 marks)

1. How ....... is it from your house to school?

A. far

B. long

C. old

D. tall

2. What ………… intelligent boy!

A. the

Three

C.an

D. is

3. Would you some coffee?- __________

A. Yes, please

B. Of course

C. No, thanks

D. Both A and C are correct.

4. This car is the ....... expensive of the four car.

A. Best

B. more

C. good

D. most

5. They enjoy .......TV.

A. to watch

B. watching

C. to watch

D. watched

6. A …………work on a farm.

A. doctor

B. farmer

C. teacher

D. journalist

7. She is very happy ....... you again.

A. meet

B. meets

C. to meet

D. meeting

8. He is in class 7A and ................................ am I.

A. too

B. so

C. but

D. by

III. Give the correct form of the verbs in the bracket. (2 marks)

1. Trang (not have) any friends in Ha noi.

2. Some boys and girls (play) marbles at the moment.

3. The students (visit) their old teacher next week?

4. Mr Nam usually (watch) TV in his free time?

IV. Fill in the blanks with the correct form of the words in the capital letters (1 mark):

1. Today Lien is not.........because she misses her parents HAPPINESS

2. Living in the city is..than living in the countryside NOISY

3. In electronics, we learn to repair. ............appliances. HOUSE

4. My. ..........is tall and beautiful. TEACH

V. Read the passage carefully then answer the questions: (2 marks)

Linda lives with her parents in a big house in HCM City. She is from England. She is thirteen. She has blue eyes and black hair. She is studying at International Language School. She can speak French, English and Vietnamese. But she doesn't speak Vietnamese fluently. She often goes to French speaking club on Sunday mornings. She s Vietnamese people very much because they are friendly.

1. Where is Linda from?................................................................................ ..............................

2. How many languages ​​can she speak?................................................................................ ..............................

3. Does she speak Vietnamese fluently?................................................................................ ................................

4. Why does she Vietnamese people?............................ ..........................

BECAUSE. Read the following passage and choose the best option for each numbered blank.

Do you want to be fitter and healthier? Would you to look younger? Do you want to feel (1) _____ relaxed? Then try a few days at a health farm. Health farms are becoming (2) ___________ of the most popular places (3) ___________a short break. I went to Henley Manor for a weekend. It's (4) ___________ largest health farm in the country but it isn't the most expensive. After two days of exercise and massage I (5) _____ten times better. But the best thing for me was the food. It was all very healthy of (6) ___________ , but it was expensive too!

If you're looking for something a (7) ___________cheaper, try a winter break. Winter is the darkest and the coldest (8) _____of the year, and it can also be the (9) ___________ time for your body. We all eat too (10) ___________and we don't take enough exercise. A lot of health farms offers lower prices from Monday to Friday from November to March.

VII. Arrange the following words to make correct sentences. (1 mark).

1. play/ will/ soccer/ this/ afternoon/ they.

................................. ..............................

2. my/ is/ favorite/ English/ subject.

................................. ..............................

VIII. Complete the following sentences with the suggested words. (1 mark).

1. It / difficult/ find/ apartment / Ho Chi Mih City?

................................. ..............................

2. They/ listen/ music/ now.

................................. ..............................

B. Answers

I. Choose the word in each group that has the underlined part pronounced differently from the rest.

1. B 2.A 3.D 4.C

II. Choose the best words by circling the letter A, B, C or D. 

1. A 2. C 3. D 4. D 5. B 6. B 7. C 8. ELSE

III. Give the correct form of the verbs in the bracket.

1. doesn't have 2. are playing 3. will visit 4. watches

IV. Fill in the blanks with the correct form of the words in the capital letters:

1. happy

2. noisier

3. household

4. teacher

V. Read the passage carefully then answer the questions

1. She is from England.

2. She can speak three languages.

3. No, she doesn't.

4. She s Vietnamese people very much because they are friendly.

BECAUSE. Read the following passage and choose the best option for each numbered blank.

VII. Arrange the following words to make correct sentences. 

1. They will play soccer this afternoon.

2. My favorite subject is English/English is my favorite subject.

VIII. Complete the following sentences with the suggested words. (1 mark):

1. Is it difficult to find an apartment in Ho Chi Minh City?

2. They are listening to music now.

Midterm exam 1 English 7 with answers - Question 4

A. GRAMMAR, VOCABULARY AND PHONES

Quesion 1:

*Choose the best answer for each of the following sentences

1. Will you ………….making models in the future?

A. pick up

B. look for

C. take up

D. find

2. His parents are always proud ............. him ?

A. about

B. of

C. on

D. with

3. Have you ever……………to Sapa?

A. goes

B. be

C. go

D. been

4. I ……playing board games interesting because I can play them with my friends.

A. think

B. find

C. drunk

D. tell

5. I watching TV ………….. it's entertaining and educational.

A. so

B. but

C. although

D. because

6. It's good to____ blood because you can save people's lives.

A. helping

B. used

C.collecting

D. donate

* Choose the word that has the underlined part pronounced differently from the others.

7. A. g oal B g old C. ori g inal D. g irl.

8. A. studio ed B. wash ed C. look ed D.watch ed

* Choose the word with the different stress syllable.

9. A. statiss B. history C. concentrate D. different

10.A. wonderful B. beautiful C. prediction D. television

Question 2: Give the right form of the verbs in brackets:

1. I (hear) ..the good news from Mary a few minutes ago.

2. ……………………..you ever (visit)……………………Da Nang ?

3. Don't worry we (go) ……………………..swimming with you tomorrow.

4. It's boring ( watch )................................. television everyday.

5. You (see) ............the film on television last night?

6. George is interested in (take)......... an art class

B. Reading

Question 1. Read the arle about Angel Falls. Then answer the questions.

Dear Mira,

Thanks for your letter. Now I'll tell you about my hobbies.

My favorite hobby is knitting. It is strange, isn't it?. My mother taught me to knit two years ago. Now I can knit scarves and sweaters. It's great when I can give them to my relatives and friends as gifts. Knitting is also imaginative because you can knit anything you can imagine of. Besides, it is quite cheap. You only need a pair of needles and some wool.

I'm sending you a scarf next month. I'm knitting it. I hope you'll it.

Best wishes,

Vy

1. What is Vy's hobby?

................................. ................................

2. Did she learn this hobby from her father?.

................................. ..............................

3. How does she feel when she can give the scarves and sweaters to her relatives and friends ?.

................................. ..............................

Question

2: Read the text and choose the best answer A, B, C or D to fill each blank .

My friends and I have written a (1) . We have decided to (2) it for our school. I have already built the set. Karen has just finished the (3) for us to wear. I haven't learned the (4) yet, so I am a bit nervous, but I'm excited too. I haven't been in a play before. I can't wait!

1.A. movie B. song C. play D. club

2 A. perform B. make C. take D. build

3.A. stage B. actors C. play D. costumes

4.A. script B. scripts C. play D. lessons

C. Writing

Question 1: Rearrange the words below to make meaningful sentenses.

1.We / collected / books / clothes / street children/ have/and/ for /used .

................................. ................................. ..............................

2. doing / finds / interesting/ he/ service / community .

................................. ................................. ..............................

3.not/ pass / did / Minh / lazy/ was / so/ he/exam/ the.

................................. ................................. ..............................

4. important / study / to / It / is / English .

................................. ................................. ..............................

Question 2: Rewrite the following sentences, beginning as shown, so that the meaning stays the same.

1/ Hoa was sick, so she could not go to school yesterday.

→ Because ……………………………………………………….

2. The last time I saw him was 3 years ago

→ I haven't ……………………………………………………….

3. I find making pottery interesting.

→ I think................................................................................. ................................. ..........

4. My sister is interested in reading comics.

→ My sister enjoys................................................................. ................................. .....

The end

Answer

A . GRAMMAR , VOCABULARY AND PHONES

Quesions 1 :

Question 2: Give the right form of the verbs in brackets:

B. R reading

Question 1. Read the text and answer the questions:

1. Her favorite hobby is knitting

2. No,she doesn't.

3. She feels great when she can give them to her relatives and friends as gifts.

Question 2: Read the text and choose the best answer A, B, C or D to fill each blank . Bottom of Form

C. Writing

Question 1: Rearrange the words below to make meaningful sentenses. Bottom of Form

1.We have collected used books and clothes for street children .

2.He finds doing community service interesting .

3.Minh was lazy so he didn't pass the exam.

4.It's important to study English.

Question 2: Rewrite the following sentences, beginning as shown, so that the meaning stays the same. Bottom of Form

1. Because Hoa was sick,she could not go to school yesterday.

2. I haven't seen him for 3 years.

3.I think making pottery is interesting .

4. My sister enjoys reading comics.

Grade 7 midterm English exam with answers - Question 5

I. Choose the word whose underlined is pronounced differently (1 mark)

1. A. c alorie B. musi c al C. c inema D. c ommunity

2. A. a g ain B. aller g y C. or g anization D. g ardening

3. A. s ch ool B. ch emistry C. ch ristmas D. ch ampion

4. A.lau gh B. rou gh C. enou gh D. nei gh bor

II. Choose the correct word or phrase to fill in each of the following (3 marks)

1. Her parents are still live there .......... her customer.

A. for B. at C. with D. on

2. Lan is ............than Hoa

A. tall B. tall C. taller D. more tall

3. ........... do you live?

A. Who B. What C. Which D. Where

4. ................. are you talking to?

A. Who B. What C. Which D. Where

5. What ............your phone number?

A. is B. are C. does D. do

6. Nga lives ............ 52 Nguyen Hue Street.

A. on B. in C. at D. under

7. ........... does your father do?

A. When B. Where C. What D. Which

8. Tomorrow my family ............ to Ho Chi Minh City.

A. is B. is going to go C.is going D. goes

9. My mother takes care ............ sick children.

A. about B. in C. at D. of

10. He works ........... the farm.

A. on B. in C. about D.at

11. Are there ......... pens on the table? Yes, there are.

A. any B. some C. much D. a

12. ............ a beautiful day!

A. It B. Which C. Where D. What

III. Complete the sentences with on, in, at, in front of (1 mark).

1. My birthday is…………..June eighth.

2. I live.........Gio Quang.

3. I get up.........6 o'clock every day.

4. My house is…………………….a lake.

IV. Supply the correct form of the verbs in brackets (2,5 marks).

My Aunt Thuy (live) ................ (1) in Ha Dong. She (work) .....................(2) in a hospital in the center of Ha Noi. Every morning, she (catch) ............(3) a bus to her hospital. Her work is (take) ....(4) care of sick children. She (love) ............(5) the children. She always (say) ............(6) that children (be) ............(7) very lovely. Now she (do) ............(8) her job with great pleasure. But next year she (go).........(9) to Ho Chi Minh City with her husband . She (be)...........(10) very unhappy.

V. Answer the questions (2,5 marks).

1. What's your family name?

................................. ..........................

2. How do you get to school?

................................. ..........................

3. How far is it from your house to school?

................................. ..........................

4. What will you be on your next birthday?

................................. ..............................

5. Where are you going to go next Sunday?

................................. ..............................

Answer

I.

1. C 2. B 3. D 4. D

II.

1. C 2. C 3. D 4. A 5. A 6. C

7. C 8. B 9. D 10. A 11. A 12. EASY

III.

1. On
2. Print
3. At
4. Print front of

IV.

1. Lives
2. Works
3. Catches
4. Taking
5. Loves
6. Says
7. Is
8. Is doing
9. Will go
10. Is

V.

1. My family name is..........
2. I go to school by bike.
3. It is about 2 kilometers.
4. I will be 14 on my next birthday.
5. I am going to to go to the zoo next Sunday.

See also: Midterm exam questions for grade 7 advanced English for 2020 - 2021 NEW

Midterm exam 1 English grade 7 - Question 6

Exercise 1: Choose the word whose underlined part is pronounced differently from the others

Exercise 2: Choose the correct answer

1. I enjoy reading ______________ it develops my imagination.

A. and

B. but

C. so

D. because

2. To help people with transportation, we can __________ rides to the elderly.

A. ask

B. give

C. donate

D. help

3. My favorite hobby is _______. I spend most of my free time making vases and bowls from clay.

A. woodcarving

B. pottery making

C. model making

D. birdwatching

4. _______ do you do volunteer work? - Every weekend.

A. How long

B. How far

C. How much

D. How often

5. Have you ever taken part _______ volunteer work?

A. for

B. big

C. in

D. with

6. She's got a high _______ – almost 40°.

A. flu

B. headache

C. sore throat

D. temperature

7. Mary is _______ weight because she eats too much junk food.

A. getting over

B. putting on

C. taking up

D. throwing away

8. Stay outdoors ________ and do _________ physical exercises.

A. more - less

B. less - less

C. more - more

D. less - more

9. Don't read or study when there is not enough light because it is ________ to your eyes.

A. harm

B. harmful

C. harmless

D. unharmed

10. My aunt often _____ money to charitable organizations to help street children and the homeless.

A. makes

B. does

C. donates

D. send

Exercise 3:Supply the correct form of the words in brackets

1. Mike's hobby is listening to music. He gets a lot ___________ from listening to music. (enjoy)

2. One third of children in the US is ___________ or obese. (weigh)

3. Junk food is ___________, so we shouldn't eat too much junk food. (healthy)

Exercise 4: Write the correct tense or form of the verbs in brackets

1. We ________________ (not do) any volunteer work five years ago.

2. I think people ________________ (eat) more healthy food in the future.

3. ______________ (Alex/ ever/ be) to Seattle? ~ Yes, he ______________ (be) to Seattle once.

4. Be a Buddy ________________ (establish) in 2011.

5. My mother enjoys ________________(do) charitable work.

Exercise 5: Read the passage and answer the questions

We send young people of different nationalities on expeditions around the world. Our volunteers get the chance to work with local people to learn about different cultures.

There are ten expeditions every year. Each expedition lasts for ten weeks and takes 150 volunteers. They go to countries such as Chile, Namibia, Mongolia and Vietnam. Some of our volunteers work with local people to provide facilities, for example, building schools. Others work in national parks or help scientists to do environmental research.

These adventurous, young people come from all over the world. To become a volunteer, you have to be between 17 and 25; you have to speak some English and you also have to be enthusias, flexible and hard-working members of a team.

1. Who goes on the expeditions?

____________________________________________

2. How many .expeditions are there every year?

____________________________________________

3. How long does each expedition last?

____________________________________________

4. What do the volunteers help scientists?

____________________________________________

5. Which language must we know to become a volunteer?

____________________________________________

Exercise 6: Rewrite the following sentences without changing its meaning

1. I spend twenty minutes walking to school every morning.

It takes ______________________________________

2. I find losing weight very difficult.

It's ___________________________________

3. He hasn't smoked cigarettes for a month.

The last time _________________________________

Exercise 7: Arrange these words to make meaningful sentences.

1. you/ Have/ finished/ homework/ your/ yet/?

_____________________________________________

2. printer/ under/ This/ guarantee/ is/.

_____________________________________________

3. vacation/ since/ We/ haven't/ last/ had/ a/ year/.

____________________________________________

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TL :

Dinh dưỡng trong ý nghĩa là vi sinh vật sử dụng nó để tiến háo giúp nó sinh sản nhiều hơn bằng dinh dưỡng của thạch agar

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Tham khảo cách giải:

Có 2 giống lúa: một giống có gen quy định khả năng kháng bệnh X và một giống có gen quy định khả năng kháng bệnh Y. Bằng cách gây đột biến người ta có thể tạo ra giống mới có 2 gen kháng bệnh X và Y luôn di truyền cùng nhau.

     Cách tiến hành thí nghiệm:

     + Người ta lai hai giống lúa với nhau rồi sau đó xử lí con lai bằng tác nhân gây đột biến nhằm tạo ra các đột biến chuyển đoạn nhiễm sắc thể chứa cả hai gen có lợi.

     + Từ đó chọn lọc cây có kiểu hình mong muốn.

     + Tạo dòng thuần chủng

Bằng cách gây đột biến thì ta hoàn toàn có thể tạo ra giống mới có cả hai gen kháng bệnh X và Y 

- Có tính di truyền cho giống kế tiếp

Cách tiến hành thí nghiệm:

Lai hai giống lúa với nhau rồi sau đó xử lí con lai bằng tác nhân gây đột biến nhằm tạo ra các đột biến chuyển đoạn nhiễm sắc thể chứa cả hai gen có lợi , sau đó chọn lọc cây có kiểu hình mong muốn để tạo dòng thuần chủng.

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A >NHA EM 

TL

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NHA

* Tính ổn định của ADN chỉ có tính tương đối vì:

+ liên kết hidro có số lượng lớn nhưng là liên kết yếu nên khi cần, liên kết hidro có thể đứt, 2 mạch đơn của ADN tách nhau ra để ADN tái sinh và sao mã.

+ ADN có khả năng đột biến ( đột biến gen)

+ Có thể xảy ra trao đổi chéo trong giảm phâm dẫn đến thay đổi cấu trúc ADN

ADN ổn định tương đối vì:

- Vì gen có thể bị đột biến (đột biến gen) thay đổi câu trúc ADN.

- Ở động vật bậc cao hầu hết ADN nằm trong cấu trúc nhiễm sắc thể mà các nhiễm sắc thể cùng cặp tương đồng thường trao đổi đoạn trong kì đầu giảm phân I làm thay đổi cấu trúc ADN

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