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Doctor's Diagnosis: X chromosomes

Chromosomes are actually just gigantic DNA molecules, very

Chromosomes are actually just gigantic DNA molecules, very tightly wound around themselves, like a tangled-up piece of spaghetti. Stretched out, all of the DNA from one single human cell would measure about six feet long. Photo Credit: iStock

My friends who are color blind are males. Every patient I have taken care of with muscular dystrophy or hemophilia was a male. Is this just a coincidence? Not really.

We often forget that each of us began when a single sperm cell fertilized a single egg. This fertilized egg somehow contained all the information needed to develop into a full-grown organism capable of reading. Where in the fertilized egg was all this information contained? The answer is in the chromosomes.

Chromosomes are actually just gigantic DNA molecules, very tightly wound around themselves, like a tangled-up piece of spaghetti. Stretched out, all of the DNA from one single human cell would measure about six feet long.

The DNA in humans is packaged into 23 pairs of chromosomes, with one of each pair coming from the biological mother and one coming from the biological father.

The so-called “sex” chromosomes make up one of the pairs. Females have two X chromosomes, with one X inherited from the mother and one from the father. Males, who are XY, have inherited an X from the mother and a Y from the father. The Y chromosome ensures the person develops into a male, but otherwise it contains little genetic information — and that’s the problem.

Diseases such as red-green color blindness, hemophilia and the commonest form of muscular dystrophy are all carried on the X chromosome. If a male inherits an abnormal X chromosome, he will develop the disease. The Y chromosome cannot compensate for the abnormal X chromosome because it does not carry any genetic information pertaining to these problems. Inheriting a single defective chromosome is enough for the male to develop these diseases.

In contrast, for a female to develop these diseases, she must inherit an abnormal chromosome from both her parents. If she has one abnormal and one normal X chromosome, the normal one prevents her from developing the disease. Since these are relatively uncommon diseases, it is unlikely — but not impossible — for a female to develop these problems.

Scientists are learning how to manipulate chromosomes. For example, most of the insulin used today is obtained from microbes that have had part of a human chromosome inserted into them so that they produce human insulin.

Until similar treatments become available for diseases such as muscular dystrophy and hemophilia, females have a decided advantage in terms of avoiding diseases found on the X chromosome.


Dr. Stephen Picca of Massapequa is Board Certified in both Internal Medicine and Anesthesiology. He is retired from practice. Questions and comments can be sent to Dr. Picca at health@newsday.com.

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