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Weekly Dose of Wonder: Why we get more genes from our moms

JUANA SUMMERS, HOST:

It's time now for our Weekly Dose of Wonder from the Science Desk. This week we're talking about genes and families. Have you ever been told you're a lot like your parents, that you're, say, your mother's daughter or your father's son? We all, of course, inherit genes from both of our biological parents, but it turns out it's not a 50-50 split. We inherit more genes from one of our parents. NPR's Allison Aubrey joins us now. Hey.

ALLISON AUBREY, BYLINE: Hi, Juana - good to be here.

SUMMERS: So, Allison, does this ring true to you? Have you ever been told that you're your mother's daughter?

AUBREY: Yeah. I became interested in this one after a recent experience. I was coming out of the grocery. I had bags in my arms, and I was standing in the back of my car, unlocking my trunk. And I kind of inadvertently caught a glimpse of my reflection in the window. And I thought, oh, my God. I jumped back. That's my mother standing there. I looked just like her. Now, people had told me that for years, but I had never seen it myself, and it was a little bit eerie.

SUMMERS: I have definitely been there before. I mean, I think a lot of us have these moments where we see ourselves in our parents. So let's turn to the science. Which parent are we, in fact, more related to?

AUBREY: To our mothers, it turns out. And the way this works is kind of cool. I spoke to a pediatrician at Duke University, Dr. Jennifer Cohen. She's trained as a medical geneticist.

JENNIFER COHEN: All people, women and men, are more genetically related to their maternal line, I would say, not just their mother but their whole matrilineal line, essentially - so their mother, their maternal grandmother and so on and so forth.

AUBREY: Now, there are a couple of ways this works, Juana. You've heard of mitochondria, the little power plants of our cells. Well, it turns out we have DNA in our mitochondria, and it only comes from our biological mothers, not from our fathers. Basically, the mitochondrial DNA comes through the egg, not the sperm.

SUMMERS: OK, tell me more. Do scientists know why?

AUBREY: Well, there's a lot of speculation, and it's not just humans. Most all mammals and other creatures inherit maternal mitochondria. And when scientists studied this in worms, they found that if mitochondria from the male is introduced, it could have a damaging effect. Here's Dr. Cohen again.

COHEN: It seems to be that there would be a problem if both mitochondrial DNA were to make it into the embryo because of the competition that would ensue between the two types of DNA, potentially.

AUBREY: So the specifics of why and how remain a bit of a mystery. And I should point out it's a tiny fraction of our genes we're talking about here. But what I think is intriguing is this understanding that we can trace our mitochondrial DNA from our mother to our grandmother, great-grandmother and all the way back, you know, through time to think how many people share a direct maternal ancestor.

SUMMERS: I mean, that is pretty cool-sounding. Allison, you mentioned that this works in a couple ways. We can inherit more genes from our mother's side. So what's the other way?

AUBREY: Yeah. Well, it turns out male offspring - so boys - inherit more genes from their mothers. The way this works is that when it comes to the sex chromosomes, females get two X chromosomes, one from their mother, one from their father, whereas males get an X from Mom and a Y from Dad. Well, it turns out the X chromosome contains a lot more genes, more than a thousand genes, whereas the Y chromosome has far fewer genes, about 100 or 200 genes.

COHEN: So technically, a male individual will have more genes from their mother than from their father.

SUMMERS: So when a person is told you're your mother's daughter or you're your father's son, well, of course they are. But understanding these differences and the genes that we inherit from both parents is, well, quite wondrous.

SUMMERS: NPR's Allison Aubrey. Thank you so much.

AUBREY: Thank you.

(SOUNDBITE OF CLOUDKICKER SONG, "LET YOURSELF BE HUGE") Transcript provided by NPR, Copyright NPR.

Allison Aubrey is a correspondent for NPR News, where her stories can be heard on Morning Edition and All Things Considered. She's also a contributor to the PBS NewsHour and is one of the hosts of NPR's Life Kit.
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