How Did You Get Five Fingers?
Your arms and toes began as tiny buds that sprouted from your sides when you were just a four-week-old embryo (胚胎). By six weeks, these limb buds had grown longer and five rods of cartilage 软骨) had appeared in their flattened tips. By week seven, the cells between the rods had died away, forming five small fingers or toes from once-solid masses of flesh.
Now, a team of scientists led by James Sharpe from the Centre for Genomic Regulation in Barcelona has discovered that these events are carefully orchestrated by three molecules. They mark out zones in the embryonic hand where fingers will grow, and the spaces in between that are destined to die. Without such molecules, pianos and keyboards wouldn’t exist, and jazz hands would be jazz palms.
These three molecules work in a way first envisioned by Alan Turing, a legendary English mathematician and code-breaker. Back in 1952, Turing proposed a simple mathematical model in which two molecules could create patterns by spreading through tissues and interacting with each other. For example, the first molecule might activate the second, while the second blocks the first. Neither receives any guidance about where to go; through their dance, they spontaneously organize themselves into spots or stripes.
Since then, many scientists have found that these Turing mechanisms exist. They’re responsible for a cheetah’s spots and a zebrafish’s stripes. For 30 years, people have also suggested that they could sculpt our hands and feet, but no one had found the exact molecules involved.
Sharpe knew that these molecules would need to show a striped pattern. Sox9 seemed like the most promising candidate. It is activated in a striped pattern from a very early stage of development. By comparing cells where Sox9 is active or inactive, Jelena Raspopovic and Luciano Marcon found two other groups of genes—Bmp and Wnt—also formed striped patterns. Bmp rises and falls in step with Sox9 and both are active in the digits. Wnt is out of phase; it’s active in the gaps. The three molecules also affect each other: Bmp activates Sox9 while Wnt blocks it; and Sox9 blocks both of its partners. It looked like these were the molecules the team was searching for not a pair, as Turing suggested, but a trinity. To confirm this, they created a simulation of a growing limb bud and showed that Sox9, Bmp and Wnt could organize themselves into a pattern of five stripes, by activating and blocking each other.
There’s still a lot to discover, though. For example, I’ve used Bmp and Wnt as shorthands here—in reality, each represents a class of several molecules, and the team still needs to work out which specific member is part of the Turing’s proposal.
1．The underlined sentence in the second paragraph means that ________.| A．some certain molecules are necessary for the growth of human fingers |
| B．the development of embryos is dependent on some certain molecules |
| C．without some certain molecules, music won’t exist in this world |
| D．the molecules work in a way that Alan Turing once offered |
| A．Molecules interact by following a strict mathematical model. |
| B．Molecules have a strong will to form patterns in nature. |
| C．The formation of patterns in nature may be dominated by molecules. |
| D．Alan Turing was able to track down the movement of molecules. |
| A．A protein that determines humans’ development in childhood. |
| B．A gene especially important for the development of our limbs. |
| C．A striped pattern that always interacts with Bmp and Wnt. |
| D．A simulation of growing limbs that activate and block each other. |
| A．How human limbs are developed may well be similar to how animal spots are shaped. |
| B．The way Sox9 interacts with Bmp and Wnt is still a mystery that needs further studying. |
| C．Sox9 can activate both Bmp and Wnt to form our limbs, according to scientific research. |
| D．Sox9, Bmp and Wnt are three specific molecules that determine the growth of fingers. |
On Dec. 20, Mello called his mother on FaceTime, which he does every day after school. That afternoon, Mello broke down in tears the moment his mother, Anita James, answered the phone.
“Mello, what happened?” James asked her son on the phone while typing something in the computer.
“I’m getting tired of them bullying (欺凌) my friend about his shoes. It’s making me so upset,” he responded in a serious voice, explaining that his classmates made fun of his friend Melvin for having worn-out muddy sneakers.
James listened to Mello’s narration with a thoughtful expression. Then, Mello earnestly asked, “Can we go buy him some shoes?”
James told her son they would talk about it when she got home from work. During their in-person conversation a few hours later, James found her son still upset. At last, Mello decided to buy his friend a fresh pair of sneakers to get rid of bullies and remind him that he has people who care about him.
“Can I use my pocket money, or you can take something away that I would get for Christmas?” Mello asked his mother.
The sincere request from her son hit James for many reasons, including that when she was growing up, her older brother used to buy her sneakers when her parents couldn’t afford them. Now, in their adult lives, James buys her brother a pair of sneakers for his birthday every year to show her gratitude. James was so touched by her little boy’s. genuine care for his friend and she knew how it would matter to the poor kid, Melvin.
That evening, they went to a sneaker store and bought a pair of black-and-white Nike shoes for Melvin. Mello used savings from his pocket money to pay for the $85 shoes.
This way, Mello thought, “nobody could laugh at him or say anything about him anymore.” Mello was so excited to give Melvin the gift that he woke up nearly an hour early for school.
Before class began, Mello handed his friend the orange Nike box in private.
Bryant Brown, the school’s social studies teacher, spotted the shoe box on Melvin’s desk.
Among all the fast growing science and technology, the research of human genes, or biological engineering as people call it, is drawing more and more attention now. Discussions about it are increasingly heated around the world.
The greatest thing that gene technology can do is to cure serious diseases that doctors at present can almost do nothing with, such as cancer and heart disease. Every year, millions of people are murdered by these two killers. And to date, doctors have not found an effective way to cure them. But if the gene technology is applied, not only these two diseases can be cured completely, bringing happiness and more living days to the patients, but also the great amount of money people spend on curing their diseases can be saved. Therefore, it benefits the economy as well. In addition, human life span( 寿命) can be prolonged.
Gene technology can help people to give birth to more healthy and clever children. Some families have genetic diseases. This means their children will for sure have the family disease, which is a great trouble for these families. In the past, doctors could do nothing about genetic diseases. But gene technology can solve this problem perfectly. Scientists just need to find the wrong gene and correct it, and a healthy child will be born.
Some people are worrying that the gene research can be used to create human beings in large quantities. In the past few years, scientists have succeeded in cloning animals such as mice, sheep, and dogs; therefore, these people predict that human babies would soon be cloned( 克隆) and that it would be beyond control, leading to some disastrous consequences. But many believe that cloned babies will not come out in large quantities, for most couples in the world can have babies in a very normal way and they also believe the governments will control gene technology and make laws to make sure the gene technology will help improve our lives instead of harming us.
At eleven years old during my summer holiday, my main concern was money. I wanted to buy the new must-have thing my classmates had. I already had a “job” as a sales representative with a kids-based sales company, and I sold wrapping paper and greeting cards with the best of them. On my bedroom floor, I arranged the bills and change from my purse to see what I had. I wished it would multiply before my eyes, but of course it didn't. I went to my mom. "Mom, I need more money,” I said, leaning against the kitchen counter while she cooked dinner.” What else can kids do for a job around here?” Mom responded with a smile, “Okay, let me ask around.”
The next day, she had an answer “Your grandmother will pay you to help her deliver lunch each day to the elderly.” Yes! I pumped my fist into the air. I couldn't wait to start my new job on Monday after school dismissed for the summer.
When my grandmother picked me up, I thanked her for the job and started asking the job. “It's simple. We pick up a large container full of hot meals in a nearby town and then we go on our delivery route,” she answered.
We arrived at the pick-up kitchen and got dozens of little shiny silver boxes with white lids that were hot. After our load was arranged in the backseat, my grandmother drove us to our first stop: a small white house. I took a meal and a small box of milk from the back and walked beside my grandmother to the front gate. She opened it and nodded to me to go in. I walked along the cracked walkway. Tall grass tickled (使发痒) my ankles.
Did someone really live here? I couldn't imagine that. The house didn't look nice, but I kept going. In front of the door leading to the enclosed front doorway, I paused, and my grandmother called out, “Mrs. Hershel, we've brought you some lunch.”
The reply in a low voice came from my left, “Come on in.”
On the road home, my grandmother said,” For some of them, we're the only person they see and a kind word and a smile go a long way.”
How to express your thanks
| A．Not completing | B．Not completed |
| C．Not having completed | D．Having not completed |
| A．Telling | B．Having told | C．To be told | D．Having been told |
I’m Li Hua, ____________________________________________________________________________________________________________________________________________________________________________________
搜索
