Cloning is a transliteration of Clone, which means asexual reproduction. The English word "Clone" comes from the Greek word "Klone", which originally meant to propagate with "shoots" or "cuttings". Now, the meaning of "cloning" is not only simple "asexual reproduction", but also refers to a group of individuals from an ancestor who have undergone asexual reproduction. This group of asexual offspring from an ancestor is also called "asexual cloning", or cloning for short. In nature, many plants have innate cloning instinct, such as sweet potatoes, potatoes, roses and other cutting propagation plants. However, animal cloning technology has experienced the development process from embryonic cells to somatic cells. Cloning technology is asexual reproduction technology. Not long ago, it was reported that Dolly the cloned sheep was cloned successfully for the first time by this technology, which opened a new page in the history of bioengineering.

Dolly's cry spread all over the world. The research team led by embryologist ian wilmut of Roslin Institute in Edinburgh cloned this extraordinary lamb from the mammary gland cells of an adult sheep.

First, Wilmatt and his colleagues scraped off several membrane cells from the mammary gland of an unknown white pregnant sheep in FenDorset. Usually, these cells can maintain their activity in 10% fetal serum; Serum is a liquid component of blood, which is rich in cellular nutrients similar to food. Wilmatt realized, however, that by using the standard technique of putting cells in a dormant state, that is, putting them in serum with a concentration reduced to 0.5%, these cells can not only "forget" that they are breast cells, but also "remember" the genetic instructions for developing into a whole sheep.

This is a major breakthrough. Previously, other scientists didn't understand the importance of keeping pace with the development of cellular genetic material. Previously, in other laboratories, genes were too advanced in the development process of egg activation. However, Wilmat cells extracted from Fenndoset ewes did not start to divide DNA and turn it into sheep material. The genes of dormant breast cells can easily combine with egg cells. Then, scientists extracted egg cells from the smaller Scottish black-faced sheep and removed their nuclei (the carrier of DNA) by surgery.

Wilmatt and his research team put the breast cells of white sheep into the egg cells of enucleated black sheep, and used Frankenstein-style technology to not only combine the membranes of these cells with electric pulses, but also instantly merge the two cells into one.

Next, the egg cells thus synthesized are implanted into the black-faced ewe by using standard artificial propagation techniques. Four months later, this little lamb that shocked the world was born. It was found that its coat color was white, suggesting that it did not belong to the same breed as its biological mother, the black-faced ewe. It took several months to examine DNA and finally confirmed that Dolly was indeed a biological replica.

Second, the development of cloning technology.

As early as 1950s, American scientists took amphibians and fish as research objects and pioneered nuclear transplantation technology. They studied the potential of cell development and differentiation and the interaction between cytoplasm and nucleus.

1960 and 1962, scientists from Oxford University in England conducted cloning experiments with an African Xenopus. The experimental method is to irradiate Xenopus laevis eggs with ultraviolet rays to destroy their nuclei, and then take out the nuclei from the intestinal epithelial cells, liver cells and kidney cells of Xenopus laevis tadpoles through superb surgery, and accurately put the nuclei of these cells into the eggs whose nuclei have been destroyed by ultraviolet rays. After careful nursing, some of these nuclear exchange eggs finally grew alive and kicking Xenopus laevis, which was not produced by the combination of sperm cells and egg cells, so it was a cloned Xenopus laevis.

1986, British scientist Wila Anderson cloned a sheep from embryonic cells for the first time through nuclear transfer, and later some people cloned animals such as cattle, sheep, rats, rabbits and monkeys. Recently, the United States successfully cloned monkeys, and Japanese scientists also claimed that they had bred more than 200 "cloned cows". All the cloned animals were successfully transplanted with embryonic cells as donor cells. At present, cloning technology has made new progress in Britain, and they have applied this technology to human hematopoiesis. The economic background of cloning technology Dr. Ross James, director of the British PPL company, said: "From the study of Dolly, we know that we can make an important component from a cell, that is, plasma." They cooperated with Roslin Institute to study a kind of cattle and sheep with human genes. They took plasma from animals first, and then replaced human plasma. This kind of transgenic cattle and sheep contains important components of human plasma. By raising, cloning or breeding these animals, stable, reliable and relatively cheap blood resources can be obtained. According to statistics, the annual value in Britain can reach10.5 million pounds. It can be said that it has benefited a lot.

Mathematics examination paper for primary school graduation examination

Fill in the blanks. 2 1%

1.During the Golden Week of May Day in 2006, Ningxia * * * received 790,000 tourists from home and abroad, and the rewritten figure was () million. The total tourism revenue of the whole region reached 530 million yuan, which was rewritten as () billion yuan, rounded to around several hundred million yuan.

The 2008 Olympic Games will be held in Beijing, China, with () days in February and () days throughout the year.

3. 4050kg = () tons 2. 15m2 = () square meters () square centimeters.

4. The base angle of isosceles triangle is 42 degrees, and the top angle is () degrees. This is a triangle with () angles.

5. Given that A=2×3×5 and B=2×5×7, the greatest common divisor of A and B is () and the least common multiple is ().

6. The product of two factors is 1.8. If these two factors expand 10 times at the same time, the product is ().

7. Congcong walking to school, walking 1.2km per hour. The ratio of walking distance to time is (): (), and the ratio is ().

8. A 5-meter-long iron wire is divided into 6 segments on average, each segment accounts for () of the total length, and each segment is () meters.

9. The circular flower bed has a circumference of 6.28 meters, a diameter of () meters and an area of () square meters.

10, obviously there are two cuboid building blocks with the same shape and size, the length, width and height are 4cm, 4cm and 6cm respectively. He pieced two blocks together to make a big cuboid. The spliced cuboid is () cubic centimeters, and the surface area is () square centimeters or () square centimeters.

Second, judge. 5%

1. The sum of the sides of the cube is 24 meters, and its surface area is 24 square meters. …………( )

2. Remove the zero after the decimal point, and the size of the decimal point remains unchanged. ( )

3. It is easy to see the quantity of various quantities and their changes, and it is necessary to draw a statistical chart of broken lines. ( )

4. The areas of two trapeziums are equal, and these two trapeziums can definitely spell out a parallelogram. ( )

5. The height of a cylinder is constant, and its volume is proportional to the radius of the bottom. …( )

Third, choose. (Choose the number of the correct answer and fill in the brackets. ) 10%

1. In the following figures, the number that reads only zeros is ................................ ().

a、305800 10 B、7 109880 C、 107200 D、50370

There is a big tree in the park, which is as high as five stories. This big tree is about ... ()

A, 5m b,15m c, 5m d,15m

3. There is a watch part with a length of 5 mm, the length of the design drawing is 10 cm, and the scale of the drawing is ().

a、 1:20 B、20: 1 C、2: 1

4, the following figure belongs to the axisymmetric figure is ()

Cost plus freight plus freight

5. In the following statement, the wrong one is ................................... ().

A, can be divided by 2, 3, 5 at the same time the smallest three digits is 120.

Add 4 to the numerator of b, and to keep the size of the fraction unchanged, add 14 to its denominator.

C, cut a 3-meter-long steel bar into 5 segments on average, each segment accounting for the total length.

D, the number of girls in the school art interest group accounts for 40% of the total number, so the ratio of male to female students is 3: 2.

Fourth, write numbers directly. 6%

98+67= 4.8-0.79= +0.2= 15-5 =

1.25×8= 1÷0.25= = 7.2÷4=

2.5× 1 ×0.4= 1- - = ÷ - 1= 12×( - )=

5. Solve equations or proportions. 6%

4.5- X= 1 3: = 1.75:X

Six, recursive equation calculation (can be simplified). 18%

( 1)4920÷24×20 (2)

(2) (4)

(5) (6)

Seven, column calculation. 8%

(1) 12.8 minus the quotient divided by 10, (2) a number is 10 greater than 2.5,

What is the difference? Find this number.

Eight, operation questions. 4%

Draw a circle with a circumference of 12.56 cm. Mark the center, radius and diameter with letters.

Nine, look at the picture and fill in the blanks by 6%

Xiaohua goes to the library 5 kilometers away from home by bike.

Borrowing books, as can be seen from the statistical chart of dotted line given:

In the picture, Xiaohua stops at () on the way to the library.

The library borrows books with () points. From home to the library,

The average speed is () kilometers per hour. Subordinate graph

The library goes home at the speed of () kilometers per hour.

Ten, comprehensive application of 22%

1. During the summer vacation, the school is going to pave the corridor with square bricks. If you use a square brick with an area of 9 square decimeters, you need 480 pieces. If you use a square brick with an area of 16 square decimeter, how many pieces do you need at least? 4% (proportional solution)

It takes 6 hours for Party A to do a job alone, and 4 hours for Party B to do a job alone. How many hours will it take them to cooperate after A finishes 13? 4%

3. The engineering team built a section of highway, and the first day, the second day,150m, the third day and three days just finished the task. How long is this road? 4%

4. The sum of all sides of a cuboid block is 108cm, and the ratio of length to width to height is 4: 3: 2. Now I want to cut this cuboid into the largest cylinder. How many cubic centimeters is this cylinder? 5%

94 students from Yuhong Primary School, led by two teachers, rented a car for a spring outing. The 54-seat bus at the station costs 432 yuan each, and the 2 1 seat van costs 189 yuan. Please help us plan how to rent a car. 5%