QUESTION: Can you see DNA under a microscope?
ANSWER: Yes, but not in detail.
“Many scientists use electron, scanning tunneling and atomic force microscopes to view individual DNA molecules,” said Michael W. Davidson, curator of the National High Magnetic Field Laboratory at Florida State University. “But even with these advanced technologies, DNA appears as a string rather than being resolvable into the individual units from which it is composed.”
New techniques are allowing the imaging of DNA with conventional optical microscopes, he said, but these methods are in their infancy.
Chromosomes, the spiraling strands of DNA that package the series of chemical bits called genes, are easily visible through a strong enough microscope if the right stain is used.
Chromosomes are best seen at the point in cell division called the metaphase stage of mitosis. At this stage, the strands are condensed and aligned in one plane. But a chromosome can contain tens of thousands of genes, and the tiny details that make the difference between the DNA of two people are not visible through a microscope.
Do dogs and cats that have been spayed or neutered live longer?
“No definitive studies have shown evidence of the extension of life” just from sterilization, said Brenda Griffin, director of clinical programs in shelter medicine at Cornell's School of Veterinary Medicine. “But the diseases it prevents are very common.”
Also, she said, “Two studies have found that the No. 1 risk factor for a pet being taken to shelter is that it has not been spayed or neutered.” The many known health benefits for male and female dogs and cats vary by gender, Griffin said.
“If it is done before she comes into heat, spaying virtually eliminates the risk of breast cancer, the most common type of cancer” in female dogs, she said. In female cats, too, breast tumors are common, and 90 percent are malignant. But a cat spayed before age 2 is one-seventh as likely to develop them. Spaying also prevents ovarian or uterine cancer. And it cancels the risks associated with giving birth.
In dogs and cats, males that have not been neutered are at risk for testicular cancer, prostate disease and hernias. Neutering also often reduces fighting, roaming and scent marking, behaviors that may land a pet in a shelter, where euthanasia is a risk.
Editor's note: Sherry Seethaler, who usually writes the Questions Answered column, is taking a break to work on a book, “Lies, Damned Lies and Science: How to Sort Though the Noise Around Global Warming, the Latest Health Claims and Other Scientific Controversies.” She will return in two weeks.
