英语听力文摘 English Digest 569、为何有些狗身上有斑点？

 　　Why Does Spot Have Spots?

 

　　In dogs with multicolored coats, white areas have no pigment¹ cells. Black, brown or yellow areas, on the other hand, get their color from special pigment cells.

 

　　When a dog is just an embryo², these pigment cells travel from the spinal³ cord to the rest of the body. A single cell then clones itself in a certain area, forming a group of cells to color the skin and fur there. In a solid black dog, groups of cloned pigment cells fit together like pieces of a jigsaw⁴ puzzle to form the black coat.

 

　　How do the pieces fit so well?

 

　　There’s experimental evidence that pigment cells space themselves out equidistantly from each other, then divide and grow to fill the areas in between.

 

　　Spotted⁵ dogs like Beagles and Fox Terriers, also known as piebalds, have no pigment cells in the white part of their coats. Either some of their pigment cells never developed, or they divided more slowly than usual.

 

　　Dogs with white just on the feet, tip of the tail and belly⁶ have a milder piebald effect. That’s because these parts of the body are farthest from the spinal cord and the pigment cells didn’t quite get that far. As adults, dogs born with this pattern may lose most of the white, because the pigment cells continue to divide and migrate slowly out to the tips of the toes and tail.

 

　　Environmental influences on the embryo like radiation or chemicals can slow the movement of pigment cells and result in spotting. However, as dog breeders know, Spot’s spots more likely are determined⁷ by Spot’s genes⁸.

 

 

　　为何有些狗身上有斑点？

 

　　杂色狗身上的白色部分没有色素细胞，而黑色，棕色或黄色部分都有特殊的色素细胞。

 

　　狗在胚胎期时，色素细胞从脊髓游离到身体其他部位。一个细胞在某个部位可以复制成一个细胞群，为该部位的皮毛着色。纯黑色的狗身上，克隆形成的色素细胞群像拼图玩具一样组合在一起，形成狗的黑色皮毛。

 

　　这些部分怎么组合得这么完美呢？

 

　　实验证明，色素细胞相互之间会等距散开，接着再分裂成长填充中间部位。

 

　　像米格鲁猎犬和猎狐犬这种有斑点的狗也叫花斑狗。它们身上的白色部位没有色素细胞。这可能是因为它们体内的一些色素细胞没有分裂生长，也可能是这些色素细胞分裂得比较慢。

 

　　有些狗只有爪子，尾稍和腹部是白色的，这是轻微的花斑。产生这种现象是因为这些部位离脊髓最远，色素细胞没有扩散那么远。出生时带有轻微花斑的狗成年后白色部位可能就不见了，因为色素细胞会继续分裂并缓慢地移动到脚爪和尾巴末端。

 

　　环境对胚胎的影响，比如辐射和化学物质，会减缓色素细胞的移动，造成花斑。但是，像饲犬者所说，花斑狗身上的斑点更多地是由基因决定的。

1 pigment   

n.天然色素，干粉颜料

参考例句：

• The Romans used natural pigments on their fabrics and walls.古罗马人在织物和墙壁上使用天然颜料。
• Who thought he might know what the skin pigment phenomenon meant.他自认为可能知道皮肤色素出现这种现象到底是怎么回事。

2 embryo   

n.胚胎，萌芽的事物

参考例句：

• They are engaging in an embryo research.他们正在进行一项胚胎研究。
• The project was barely in embryo.该计划只是个雏形。

3 spinal   

adj.针的，尖刺的，尖刺状突起的；adj.脊骨的，脊髓的

参考例句：

• After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天，就已经使脊椎骨变得富有弹性了。
• Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。

4 jigsaw   

n.缕花锯，竖锯，拼图游戏；vt.用竖锯锯，使互相交错搭接

参考例句：

• A jigsaw puzzle can keep me absorbed for hours.一副拼图就能让我沉醉几个小时。
• Tom likes to work on jigsaw puzzles,too.汤姆也喜欢玩拼图游戏。

5 spotted   

adj.有斑点的，斑纹的，弄污了的

参考例句：

• The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。
• Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

6 belly   

n.肚子，腹部；(像肚子一样)鼓起的部分，膛

参考例句：

• The boss has a large belly.老板大腹便便。
• His eyes are bigger than his belly.他眼馋肚饱。

7 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

8 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪