The Human Embryo
In the United States alone there is an average of about four million people born every year (http://www.cdc.gov/nchs/releases/02news/womenbirths.html). In a normal pregnancy the human embryo goes through a very complicated process. During the nine months of pregnancy the embryo develops all the basic things, such as the heart, liver, and brain, that it needs to live in the outside world.
A nine-month pregnancy is divided, by doctors, into three trimesters of equal length. During each trimester the baby goes through different developments and continues to grow. The first trimester is considered the time from conception to 13 weeks. Second trimester takes place from week 13 through week 29. The final trimester is week 29 through delivery, which is usually 38-40 weeks after conception.
Throughout a woman's lifetime, from puberty to menopause, she will ovulate about 400 times. To conceive a baby, the woman's ovum must be fertilized within 24 hours of when it was released.
This, however, does not mean the woman has to have sexual intercourse the day the ovum is released. Sperm can last several days inside the woman, so having intercourse even 4-5 days before ovulation can cause conception (Nilsson 31). Fertilization is the moment one sperm penetrates the ovum. At that same moment the DNA of the mother and father mix to form the genetic code for a brand a new human being (http://www.Standupgirl.com).
The sperm that penetrates the egg controls gender. Every female egg contains one X chromosome. Every sperm either contains one X or one Y chromosome. To be a male one X and one Y chromosome must be present. To be female two X-chromosomes are present. At the moment of conception the gender is decided. From that point on it can not change. All of the time there is...