I have a scientific theory that the bonds that tie mothers and daughters are love and worry, like the two strands in the double helix of some very twisty DNA.

In other words, if I love you, I worry about you. And vice versa.

Let me explain.

The moment Daughter Francesca was born, I started to love her and worry about her. And my worry, like my love, had no bounds. I worried if she was sleeping too much. I worried if she was sleeping too little. Same with crying, nursing, and pooping. If I was breathing, I was loving, and worrying. And my biggest worry, of course, was whether she was breathing. I'm not the only mother who has watched her baby sleeping to see if her chest goes up and down.

I still do that.

My theory also applies to grandmothers. Because they're mothers, too. Just grander.

Mother Mary worried about Francesca, and all of our conversations back then were consumed with my worries and hers, and together we aimed our laser beams of worry on this hapless infant, which is undoubtedly why she turned out so great.

Or guilty.

But that's not the point, herein.

The point is that Francesca knows we worried about her - uh, I mean, we loved her.

Likewise, I know, in turn, that Mother Mary worries about me. She worries that I work too hard. She worries when I fly. She worries when I drive. She worries when I'm not at home, and even more when I am at home. For example, she worries that I could put too much food on my fork and choke.

Let me suggest that this last worry isn't so dumb. You've never seen me eat.

I used to feel guilty that she worried about me, but now I don't.

She should worry about me, constantly.

It proves she loves me.

I realized this when I understood how much I still worried about Francesca, even though she's living in New York, on her own. I don't mean to make her feel guilty, and she shouldn't. But I can't help it.

Motherhood has no expiration date.

And what just happened is that the worry has boomeranged, so that I'm starting to worry about Mother Mary.

Well, not starting.

But recently my worry, and my love, has come to the fore, because of Mother Mary's health. In particular, her nose.

It's blue.

No joke. The last time she came to visit, the first thing that I noticed was that her nose had a distinctly bluish tinge. I told her so, in a nice way, and she told me to shut up.

But still, I worried, big-time. Her circulation has never been good, due to a lifetime of smoking, but she finally quit at age 82, when she got throat cancer.

Better late than never.

Anyway, she beat the cancer, which is remarkable enough, but she's supposed to use oxygen at night, according to the doctor. But she won't do it. Our conversation today on the phone went like this:

"Ma, why won't you use your oxygen?"

"I don't like the tube. It smells like popcorn."

"So what? Popcorn is good. Who doesn't like popcorn?"

"I don't, and that's what it smells like, so forget it."

"But it's doctor's orders, Ma."

"Hmph! What does he know?"

I don't know where to begin. "Everything?"

But Mother Mary wouldn't listen, even though I eventually raised my voice, which is another thing that mothers/daughters do to prove our love.

If I'm yelling at you, you know I love you.

Because I want your chest to keep going up and down, whether you're my daughter or my mother.

Or whether I'm your daughter or your mother.

It's all the same emotion, which is worry.

Or love!

So the next time your mother is worried about you, don't tell her to shut up.

And don't feel guilty, either.

Try and understand. She can't help it. It's in her DNA.

Chalk it up to mom genes.

Lisa Scottoline and Francesca Serritella's essays have been published in "My Nest Isn't Empty, It Just Has More Closet Space" and "Why My Third Husband Will Be a Dog." Visit Lisa at www.scottoline.com.