Answer Man

Could children of O-positive parents be O-negative? Positively

By Roger Schlueter - News-Democrat

Q. My question is about blood types. If both husband and wife are O-positive, can they have children who are O-negative? — Jan Jones, of Belleville

A. Before I delve into the science, let me quickly stop any tongues that might be wagging if you are asking about a paternity debate: Yes, two O-positive parents could have any number of O-negative children. In fact, according to the experts, most children who are O-negative have parents who are O-positive.

Doesn’t seem logical, does it? You’re probably thinking that the laws of inheritance would decree that, say, if both parents had a certain trait — blue eyes, for example — their children would, too. Sort of like if both Mom and Pop were skilled musicians, you’d expect their offspring to become little Yo-Yo Mas.

But as Austrian monk Gregor Mendel found out in the 1860s, Mother Nature is complicated when it comes to genetics. In working with the seed color of peas, for example, he found that his plants had about a 75 percent chance of having yellow seeds and only a 25 percent chance of being green.

Why? Two basic reasons: inheritance and dominance. Let’s say you’re a pea. You inherit a seed-color gene from both parents. So you can wind up with a yellow-yellow, green-yellow or green-green combination.

Obviously, if you inherit the same color gene from both parents, you’re going to be that color. But what if you wind up with green from Dad and yellow from Mom? Gregor discovered that the yellow gene is dominant. Like a playground bully, it always takes over while the recessive green gene runs and hides, so to speak. That’s why, Gregor found, most of his pea plants were yellow. It took two green genes for a green-seeded plant.

While far more complex, the genetics of human blood basically can be boiled down the same way to satisfy your curiosity.

First off, another Austrian scientist, Karl Landsteiner, is usually credited for discovering the A, B and O blood types in 1900 while the AB was uncovered two years later. Like the pea example, a child inherits a blood-type gene from each parent — a total of 16 possible combinations (four possibilities from each parent).

These combinations could result in any one of 42 possible blood-type outcomes of A, B, AB or O. (You’ll have to trust me on this one; I don’t have space to list all the possibilities.) Suffice it to say that A, B and AB are dominant over O, so children will be type O only if they inherit O-type genes from both parents. Children who inherit an A-O combination will be type A, but, remember, they could still pass that O gene off to their children. As a result, their child could wind up as type O if the other parent passes them an O-type gene, too.

That last fact explains how O-positive parents can have O-negative kids. In addition to the A-B-O system, humans also have what is known as an Rh factor, which was first discovered in the rhesus monkey (hence, Rh). Here again, inheritance and dominance come into play.

In the very simplest terms, you inherit a positive or a negative Rh type from each parent. So, you could wind up with two positives, two negatives or a positive-negative mix. The positive gene dominates, so a positive-negative combination will result in a positive type as well as having two positives. Only two negatives will produce a child with a negative type.

But here is what is crucial to remember: A parent who has a positive-negative combination still can pass that negative gene to his or her children. Yes, Mom or Dad may be positive, but that recessive negative gene is still floating around in his or her DNA. If it becomes paired with another negative gene from a similar positive-negative parent, that child will be negative even though both parents are positive.

It’s an everyday occurrence, says pediatrician Dr. Alan Greene on his often praised website,

“In fact, most children who are O-negative have parents who are positive, since the positive-negative combination is so much more common than the negative-negative combination.”

So, from a typing standpoint, you can be positive the parents can be who they say are.

Q. Some time back, you ran an article about a man who takes old bicycles, fixes them up and gives them to deserving kids. Unfortunately, the day he was collecting them at the (then) Methodist church on Frank Scott Parkway, I could not get there. Now, I still have two cluttering up my storage shed. — Ron Davis

A. Considering that story ran in 2010, you must have a steel trap for a memory. But it wasn’t a metro-east man who was collecting them; the church was working through St. Louis Bworks, a nonprofit organization that takes donated bikes, fixes them up and gives them to disadvantaged youngsters — after teaching them about safety and maintenance.

It’s at 2414 Menard St. between Seventh Street and I-55 south of downtown St. Louis. For information, call (314) 827-6640 or go to But you don’t have to travel across the river: The Bike Surgeon at 3348 Green Mount Crossing in Shiloh (622-1693) tells me it still accepts bike donations for Bworks, too.

Today’s trivia

True or false: There is a Duffy blood type.

Answer to Tuesday’s trivia: In 1856, noted explorer and military officer John Fremont was asked to be the Democrats’ presidential nominee. Instead, Fremont, a staunch abolitionist, decided to become the first candidate for the new Republican Party that had been formed in 1854. Using a slogan of “Free Soil, Free Men and Fremont,” he was soundly beaten by James Buchanan in a three-man race that saw third-place finisher Millard Fillmore snag 22 percent of the vote.