DC 2007-04-04, In The Womb 子宫日记 2

(4'45-9'48)

Each month a woman's ovaries (卵巢) release one egg that contains her own genetic code. She made these eggs while she was still a fetus herself, nestled inside her own mother's womb. And they've been kept in storage ever since, through childhood, adolescence and adulthood, ready to burst into life.

nestle: to settle comfortably
ado'lescence: 青春期

How the sperm find their way to the egg is something of a mystery. Recent research indicates that sperm have a sense of smell and can sniff their way to the egg. The journey is so long and arduous for the sperm that only a handful survive. It may take up to ten hours before the actual moment of conception. The first sperm to reach the egg are the strongest and fittest, and the first to burrow its head through the egg surface will be the winner. There are no prizes for coming in second. The instant one sperm enters the egg, it triggers a change in the egg's membrane, making it impenetrable to all other sperm, which all die off within a week.

sniff: to perceive or detect
arduous: difficult

Once within the egg wall, the sperm's nucleus is drawn toward the egg's. The two cells gradually and gracefully become one. This is the moment of conception, when an individual's unique set of DNA is created- a human signature that never existed before and will never be repeated. The genetic code is stored in these bundles (捆) called chromosomes, 23 from the mother and 23 from the father. Each chromosome is made of a tightly-coiled strand of DNA. This molecule, shaped like a double helix （双螺旋）, carries our genetic code. Each microscopic chromosome contains over six feet （two meters）of DNA. A pattern of chemical codes creates this twisting ribbon of DNA and holds the key to our uniqueness- our genes.

It takes between 20,000 and 25,000 genes to make a human, roughly the same number as a chicken. All of us have a complete set from each of our parents, deep in the nucleus of every cell in our bodies. Our genes are a set of instructions that tell us to become a human rather than a fish or a tree, as well as deciding exactly what kind of person we will be. Each gene or combination of genes is responsible for a specific trait- whether our baby girl will have her mother's hair and strands or her father's eye color and long fingers.

Some genes will be dominant, others completely hidden, making each one of us physically and genetically unique. Our parents make an equal contribution to most of our genetic makeup. But the sex of the child is determined solely by the father. The 23rd pair of chromosomes has the specific job of determining sex. The sex chromosome that comes from the mother is always the same, type X. But the chromosome that comes from the father could be one of two types, X for a girl, or Y, a much smaller chromosome, for a boy.

An X sperm won the fertilization race for these parents and they are going to have a girl. The genes she's inherited have already predetermined her looks and much of her character- whether she is stubborn, intelligent, a thrill seeker or good at music, and even her vulnerability to certain diseases like cancers, schizophrenia (精神分裂症) or diabetes. The exact course of her life will depend on such things as her friends, family and environment; but at the instant of fertilization, much of her future is predetermined.

words and phrases:

burrow : To move or progress by or as if by digging or tunneling