时间:2019-01-09 作者:英语课 分类:自然百科2009年


英语课

 Hi, it’s Kasey-Dee Gardner for Why? Tell Me Why? This week we received a question about baby eye color. The question was “why are most babies born with blue eyes?”.


And I wasn’t sure that was a true statement, but it is in fact a true statement.
 
Actually we think most babies are, I don’ t have an exact number for you, and to understand why, you have to understand where the color of the eye comes from.
 
The color of the eye is determined 1 by the pigment 2(色素) which is color particles in the back part of the iris 3(虹膜), and pigment in the main tissue of the iris. And these develop actually separately. So when a baby is born, the pigment in the back part of the iris, of the healthy iris, is already formed, and the pigment in the main tissue of the iris isn’t. This pigment is called melanin(黑色素).
 
A baby would be born with pigment right here on this bottom layer. And they would all be born the same way. Everybody has the cells that make melanin.
 
In the people who have blue eyes, those cells are just not activated 4 to produce the melanin. And that’s determined by their genes 5. In babies who go on to have brown eyes by six months or a year, their genes have determined that their cells will produce melanin and that happens over that first year of life. In babies who go on to have blue eyes, their cells are not programmed by the genes to produce melanin. And their eyes will remain blue as they were at birth.
 
So how many cells are stacked in there, how hard the light, how much the light has to do to get through all those cells, will also impact and it will create shades, of greens and blues 6 and browns and hazels, because the light is bouncing around a lot.
 
So this is actually across races? Uh this is a, this has been normal development cycle of the eye. So a baby who will have darkly pigment in skin, and darkly pigment at eyes, ah, I say the one, one year mark, can be born with blue eyes, simply because the melanin has not yet been generated in the tissues of the iris.

adj.坚定的;有决心的
  • 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。
n.天然色素,干粉颜料
  • 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。
n.虹膜,彩虹
  • The opening of the iris is called the pupil.虹膜的开口处叫做瞳孔。
  • This incredible human eye,complete with retina and iris,can be found in the Maldives.又是在马尔代夫,有这样一只难以置信的眼睛,连视网膜和虹膜都刻画齐全了。
n.基因( gene的名词复数 )
  • 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
n.抑郁,沮丧;布鲁斯音乐
  • She was in the back of a smoky bar singing the blues.她在烟雾弥漫的酒吧深处唱着布鲁斯歌曲。
  • He was in the blues on account of his failure in business.他因事业失败而意志消沉。
学英语单词
a giggle
accumulative formation
Aconitum napellus
anap
antrum of Willis
auligen
ballygalleys
before the dawn of
bitchlike
black radish
breakfasts
Bredia sinensis
Bumbu
captain's table
caryozoic
catherine
Chaungzon
chondracanthus intermedius
Cinnamomum camphora
constant system
consultants' office
Cyprinodon
Dakar Canyon
differential pressure device
double-precision aithmetic
Dupuytren's suture
dust-bowl
elastic brace
electrode adjuster
end of anticline
enzootic ovine abortion
european wood mice
exparte summon
external payment
facial image
farren
fence mending
flight characteristics test
flood channel storage
flouke
garveyites
gas-fired crucible furnace
genus Artemia
gluten-free diet
heedfully
hem about
high speed disc atomizer
high-proof
hyperphoria
Ignatius of Loyola
imilchil
isotopes
jobs for the boys
keg-
leptocercal
light pattern
Ligonchio
lobations
lordoscoliosis
Mahommet
meshuge
microcomputer reset command
mokoshes
narrow angle luminaire
nicotelline
nicotinic acetylcholine receptor
nonreply
NTL (non-threshold logic)
orific union
ozakis
personal video station
perspectivization
power distribution plan
prestissimo
pundonor
quick-silvers
racquetball
record break
relaxable
screw-mounted fuel injector
sedimentation time
servulate
size class
snow protection plantation
squitchin
standard repair method
stultitious
subsurface
tactic change
the suburbs
three-way system
tidal river
triple rear vault
tugrugs
two-way radio
typhlomegaly
veganarchism
voice warning system
Vulpian's test
xylophory
zetta-coulombs