参考资料
Each month a woman's ovaries release one egg that contains her own genetic code. She made these eggs while she was still re-feed herself nascenced inside her own mother's womb. And they've been kept storage ever since through childhood, adolescence and adulthood ready to burst into life.
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 10 hours before the actual moment of conception. The first sperm to reach to the egg are the strongest and fadest. And the first of borrow its head through the egg * 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 membering, making it impenetrable to all other sperm which all die off within a week.
Once within the egg wall, the sperm's nuclear has drawn toward the eggs. 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 had never existed before and will never be repeated. The genetic code is stored in these bundles called chromosomes, 23 from the mother and 23 from the father. Each chromosome is made of a tightly coiled strand of DNA. This microcurie shaped like a double helix carries out genetic code. Each microscopic chromosome contains over 6 feet 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 thousand and 25 thousand 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 nuclears 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 trade. Whether or our baby girl will have her mother's hair and strength or her father's eye color and long fingers.
Some genes will be dominated, others completely hidden, making each one of us physically and genetically unique. Our parents making equal contribution to most of our genetic makeup. But the * of the child is determined solely by the father. The 23rd pair of chromosomes has the specific job of determining *. The * chromosome that comes from the mother 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 chromosome 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 stuggy, intelligent, a * seeker or good at music and even her vulnerability to certain diseases like cancers, * 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. |
