Dr. Oz and Dr. Roizen on Pregnancy and Your Genes

In fact, conception ismore likely to happen if sex occurs a couple days before the egg is released from the ovary.

If all goes according to plan, the sperm meets the egg in the Fallopian tube, and the two half genomes unite to form a complete set of genes containing all the DNA necessary to make a new human being. The fertilized egg says thank you very much and moves along to the uterus. There it will attach to the uterine lining and begin the amazing process of becoming a baby.

YOU-ology: A New Approach to Genes

One of the most miraculous processes in nature, aside from the formation of such things as the Grand Canyon and the hammerhead shark, has to be how we grow from a single fertilized egg cell to the trillions of cells that make up a new person.

Human cells have twenty-three pairs of chromosomes, structures that hold our DNA. The DNA acts as a complete set of instructions that tells our bodies how to develop. Individual genes are short sequences of these instructions that regulate each of our traits. As you might imagine, given the fact that virtually every person in this world looks different from every other, the nearly infinite possible combinations of maternal and paternal DNA are what give us our individuality.

minute before and forty-five minutes after their partner's ejaculation have a higher tendency to retain sperm than those who don't have an orgasm.

CLICK HERE to read more from "YOU: Having a Baby" and to view all of the charts, diagrams and images from the chapter.

Excerpt: 'YOU: Making a Baby'

When maternal brown eyes and maternal red hair get paired with paternal blue eyes and paternal blond hair, there are four possible combinations for offspring, right? Brown eyes–blond hair, brown eyes–red hair, blue eyes–blond hair, blue eyes–red hair. Extrapolate that scenario out to twenty-three chromosomes, and the possible combinations become mind-boggling, unless scientific notation is your thing: 2 23, or about 8.3 million, combinations -- meaning that there's about a 1 in 8 million chance that the same mother and the same father would have two kids with the exact same coding (excluding identical twins).

But that's only part of the story. Consider identical twins. They get dealt exactly the same DNA, but they may develop different traits down the line: One may have allergies and the other may not, one may develop a particular disease and the other may not, one may be able to play the piano without ever learning how to read music, while the other can't carry a tune with a dump truck. What accounts for these differences? Something in their environment -- potentially as early as in utero -- affected the expression of their genes differently. That something is called epigenetics.

Here's how it works:

Each cell in the human body contains about 2 meters of DNA that's packed into a tiny nucleus that's only about 5 micrometers in diameter. That's the rough equivalent of stuffing two thousand miles of sewing thread into a space the size of a tennis ball. As with thread, DNA is wound around spools of proteins called histones. Not all of your DNA gets expressed, or used to create proteins, in every cell; in fact, most of the spools of DNA in each cell are stored away, some never to be seen or heard of again.

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