Читать книгу Sex For Dummies - Pierre Lehu A., Dr. Ruth K. Westheimer - Страница 45

Now that you’ve had a chance to look at the diagram and can picture in your mind’s eye the journey that the spermatozoa take, I have to tell you about one more important transformation that they make.

All of our cells have the complete code of genetic material, called DNA (the long term is deoxyribonucleic acid, but DNA is much easier to say), unique to each individual. But while the germ cells start out with all of this DNA, along the way they undergo a process called meiosis (pronounced “my-oh-sis”). Here are some of the important effects of meiosis:

 When a germ cell undergoes meiosis, it forms two new cells, each of them having only half of the DNA code: 23 bits of genetic material (called chromosomes) instead of the normal 46.

 When a sperm teams up with a female egg, which also only has 23 chromosomes, their genetic materials intertwine, and the resulting baby ends up with a package containing a total of 46 chromosomes that is a mixture of both the mother’s and the father’s genetic material.

 When the male germ cells divide, the sex chromosomes divide also. The male has one X and one Y chromosome; the female has two X chromosomes.

 Whether the sperm that reaches the egg first has an X (female) or Y (male) chromosome determines whether the baby will be a girl or a boy.

All of you macho men out there may appreciate knowing one more thing about a spermatozoon (a single, fully developed sperm; spermatozoa is the plural): Not only can sperm move around on their own outside the body, but they’re also fully armed, like little guided missiles. Over the head of the sperm lies the acrosome, which is full of enzymes that help the sperm penetrate an egg if it should be so lucky as to meet one on its journey.

When they’re ready, the sperm leave the testes (another name for testicles) and enter the epididymis, which is a series of tiny tubes that lie on top of the testes. (For those of you into amazing statistics: If unfurled, these tubes would reach 60 feet in length.) During their journey through the epididymis, sperm learn to swim. They enter the epididymis with useless tails and leave it as little speed demons. (See the advice that practice makes perfect lies at the very heart of human life.)