Sperm determine a baby's sex.
In 2006, the Centers for Disease Control and Prevention reported that 4,265,555 babies were born in the United States. When a woman is pregnant, much of the process is shrouded in mystery and wonder, including the sex of the fetus. Theories abound regarding the determination of gender and whether the parents can affect the baby's sex.
Chromosomes
There are two chromosomes that play a role in determining sex: the X and Y chromosome. A set of two X chromosomes define female characteristics, while an XY combination designates male traits. These sex chromosomes are part of the 23 pairs normally found in human DNA strains.
Conception
Gender is determined at the point of conception when a sperm permeates an egg. The woman's egg carries an X chromosome; the sperm that meets the egg carries either an X or Y chromosome.
Development
As the fetus rounds out its sixth week of development, it starts forming male or female reproductive organs. If a Y chromosome is present, a gene within the chromosome called SRY will commence a chemical reaction to stimulate male hormones. The presence of an X chromosome or the absence of the SRY gene will trigger the production of female hormones.
Gender Selection
Through a controversial method of in vitro fertilization, parents may be able to choose the gender of their baby. During this process, sperm with male and female chromosomes are separated, and the desired sperm are injected into an egg. The technique is not foolproof: There's a possibility that the parents will still get a child of the opposite sex.
Gender-Choosing Theories
Common theories of gender selection by sexual partners include sexual position, time of ovulation and diet. According to the Mayo Foundation for Medical Education and Research, none of these theories have been proved. However, these factors may offer motivation for those hoping to have a hand in their child's gender.
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