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

Photo: Book Cover: YOU: Having a Baby: The Owners Manual to a Happy and Healthy PregnancyCourtesy Amazon.com
Dr. Mehmet Oz and Dr. Michael Roizen's latest book is "YOU: Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy."

Dr. Mehmet Oz and Dr. Michael Roizen have a new book out tackling pregnancy, called "YOU: Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy."

Read the excerpt below, and then head to the "GMA" Library to find more good reads.

Nice Genes

Back in tenth-grade biology class, you were probably taught -- as were we -- that the unique combination of genes you received from your mom and dad (your genotype) was responsible for everything that followed: the color of your eyes, the size of your feet, your love of lasagna, your hatred for all eight-legged and no-legged creatures. To a certain extent, that's true, but over the past few years, studies have suggested that classical genetics may be only part of the picture.

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It's not just your genes that determine who you are, but which of those genes are turned on, or expressed, and to what degree they are expressed -- a cutting-edge field called epigenetics. While you can't control which genes you pass on to your child, you do have some influence over which genes are expressed, affecting what features are seen in your baby (his phenotype).

In this chapter, after giving you a brief refresher on the basic biology of what happens after your life-changing evening of romantic rasslin', we're going to introduce you to a new subject: YOU-ology -- how what you eat, breathe, and even feel can affect the long-term health of your child.

Two to One: The Biology of Conception

We trust that you know the ins and outs of the process that involves his part A and her part B, so we'll skip what happens deep under the satin sheets and focus on the miracle deep below the flesh and deep inside the body -- that is, how the egg and sperm come together.*

The Eggs

On the female side of the conception equation lie her eggs, which are fully formed and stowed away in her ovaries from before birth. Each mature egg contains one copy of each gene in the human genome -- half the amount necessary for life. The maximum number of eggs that a woman will ever have is the number she has when she is a twenty-week-old fetus. She'll have about 7 million of them then, 600,000 when she's born and about 400,000 at puberty. Once a woman hits puberty and menstruation begins, her ovaries release one of those eggs every twenty-eight or so days. During each cycle, even though multiple eggs start to develop, hormonal signals ensure that only a single egg will be released and the other eggs will regress.

(It's not wise evolutionarily to blow them all at once, so the body gives females an approximately thirty-year window in which to conceive.) Hormones also work to mature that ready-to-drop egg and to pop a hole in its sac. That hole works as an escape hatch, so the egg can slip out of the ovary and travel down the Fallopian tube, where it may be fertilized by sperm.**

Tissue left behind in the ovary after the egg is released, called the corpus luteum, will produce hormones essential to successful pregnancy if the egg is fertilized.

* Please cue "Let's Get It On" by Marvin Gaye. **Interestingly, too little of these hormones may lead to infertility or miscarriage, while an abundance may lead to twins and other multiple sets.

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'

The Sperm

On the other side of the equation, of course, we have those little swimming sperm. As with a woman's eggs, each sperm contains a single copy of each gene in the human genome.

Unlike women, men don't have a preset number of their reproductive players. In fact, a man produces more sperm in each ejaculation than the total number of eggs that a woman is endowed with for life. (evolutionarily, a man can continue reproducing for the majority of his adult life, maximizing the chance of passing on his genes.

A woman's reproductive life is limited to the younger years of her life because of the physical strain of pregnancy, childbirth, breast-feeding, and child rearing.)

A man's sperm, which is carried in semen that's made by glands such as the prostate, is stored in a duct called the vas deferens. When a man ejaculates, the sperm-carrying semen fires out through the urethra in a seek and-conquer mission. It may seem that all these millions of sperm are racing one another to the finish. But just like a tour de france cycling team, the sperm have different roles.

Some are deemed the leaders of the pack, trying to be the first to cross the line. Others are designed to assist, specifically by blocking other men's sperm from making it to the finish line. Competitive little game going on in there, eh? The goal of pregnancy, of course, is for a sperm to find an egg during a precise window of opportunity and fertilize it.

The Union

The purpose of an orgasm isn't solely to make you feel good or provide gossip fodder for the neighbors. The biological purpose is to better the odds that this union between sperm and egg takes place.

On the woman's side, the mucous membranes that line the vaginal walls release fluids during intercourse so that the penis can slide with just the right amount of friction. As intensity and sensations build, the woman's brain tells the vagina and nearby muscles to contract. That contraction brings the penis in deeper. Why does that matter? It increases the chance of his sperm getting closer to the target.

During an orgasm, the cervix, located at the top of the vagina, dips down like an anteater and sucks semen up into the cervix (the cervix is a passageway connecting the top of the vagina and bottom of the uterus). The sperm is trapped in the cervical mucus until the release of the egg, and a signal then lets the sperm start the competitive swim up into the uterus. While it's by no means necessary to have an orgasm to get pregnant, women who orgasm between one 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'

On the man's side, orgasm is required, because during orgasm fireworks in the brain cause involuntary contractions in lots of muscles in his body. Those contractions help him penetrate deeper and squeeze the prostate to eject sperm deep into the vagina.

Now, the actual fertilization process happens this way: After the egg drops from the ovary, it travels through the Fallopian tube, where there's about a twenty-fourhour window when it can be fertilized. Since sperm live for up to a week in the cervix (they die after a few minutes of hitting the air), it's not necessary for two people to have sex precisely when ovulation occurs, as many assume.

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.

A good way to visualize the process: Let's say that you and your partner each comes to your relationship with a set of favorite family recipes. You may contribute a blue-ribbon chili recipe, and your significant other may bring a killer lemon meringue pie to the table. But it's not just two recipes, it's hundreds, maybe thousands. (The human genome has some twenty to thirty thousand genes, after all.)

Some on index cards, some in books, some on torn-up shreds of cocktail napkins. So what do you do with all these cranberry mold recipes? Stuff each and every one of them in the kitchen drawer. Now it's hard to sift through them, you don't have access to many of them, and you really can't find what you want.

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'

Unless ... (you knew there was an "unless" coming) you get them organized, say, by sticking hot pink Post-it notes on the recipes you really want to access quickly.

You tag your favorite recipes, so you can quickly search, find, and put them into action.

That's the way epigenetics works.

Genes are like recipes -- they're instructions to build something. Both mom and dad contribute a copy of their entire recipe book to their offspring, but for many genes, only one copy of each recipe will be used by the baby. Mom and dad have the same recipes (one for eye color, one for hair color, one for toenail growth rate, and so on), except they may have slightly different versions of those recipes (they're called alleles). For example, eye genes are either brown or blue or green.

For such genes, you express only the gene from your mom or dad -- that is, only one copy is active, but not both. In some cases, neither copy will need to be expressed: Eye color matters only to eye cells; a liver cell doesn't need either mom's or dad's eye color gene to be cranking away.

So how does a cell turn off the 24,999 genes it doesn't need and turn on the few it does? Every cell -- and there are around 200 different types in the body -- needs to know which few genes are relevant for it, and, of those genes, whether mom's or dad's is going to be expressed. As with the kitchen drawer full of recipes, the genes alone are useless unless there's a way to find what you need when you need it. There is. Your body puts biological Post-it notes called epigenetic tags on certain genes to determine which genetic recipes get used. This tagging happens through a couple of chemical processes (such as methylation and acetylation), but guess what?

Actions you take during your pregnancy influence these processes and determine where the Post-it notes go and which genes will be expressed, ultimately affecting the health of your child.

When DNA gets tagged, it changes from being tightly wound around those histone proteins to being loosely wound, making the genes accessible and able to be expressed. At any given time, only four percent of your genes are in this accessible state, while the rest can't be actively used in the body. By determining which genes are turned off and which are turned on, epigenetics is what makes you unique.

Here's a point that will help you put epigenetics in perspective: We share 99.8 percent of the same DNA ask a monkey, and any two babies share 99.9 percent of the same DNA. Heck, we even have 50 percent of the same DNA as a banana. So genes alone cannot explain the diversity in the way we look, act, behave, and develop. How those genes are expressed plays a huge role in how vastly different we are from monkeys and how explicitly and subtly different we are from one another.

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

Excerpted from You Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy by Michal Roizen and Mehmet Oz. Copyright © 2009 by Michael Roizen and Mehmet Oz. Excerpted with permission by Free Press, a Division of Simon & Schuster, Inc.