Thanks Mom!

Like Mother, like baby!
Photo from freedigitalphotos.net.

Moms give us so much more than we ever give them credit for. Biologically speaking, we all have a mom and a dad (unless you’re a flatworm or some other species that can reproduce without sex) that provide us with one of each chromosome type (our chromosomes contain our genes, commonly thought of as our “biological blueprints”). So it makes sense that we tend to think of ourselves as being half-our-mom and half-our-dad. But not so! All of us are slightly more-our-mom and slightly less-our dad.

Our genes are encoded in our DNA, which is coiled and tightly packed into dense little chromosomes. Most of our cells contain 23 different pairs of chromosomes (for a total of 46), and one from each pair comes from each parent. One of those pairs is the sex chromosomes. Individuals with two X sex chromosomes are genetically females and individuals with an X and a Y sex chromosome are genetically male. Because genetic males are the only ones with Y chromosomes, all Y chromosomes are inherited from dad. But compared to X chromosomes, Y chromosomes are piddly little things that don’t contain as many genes. So if you’re a guy, you already have more genes from mom than from dad.

In addition to our 46 chromosomes that we keep in the nucleus of each cell, we also have a tiny set of genes in another cell structure, the mitochondria. This mitochondrial DNA is only inherited from the mother, so regardless of whether you are XX or XY, you have a few more genes from mom than from dad.

Wait! My genes are where??
Your genes are lined up on the doubled-stranded DNA, which is tightly coiled and packed into
chromosomes. You have 23 different pairs of chromosomes, where one of each pair came from
mom and the other came from dad. A copy of each of these 23 pairs of chromosomes
(46 chromosomes in total) is in the nucleus of every cell you have (except for sperm or egg cells,
which only have one of each pair, or 23 chromosomes in total). Get it?
Figure adapted from an image by KES47 at Wikimedia.

But we are not simply a product of our genes. If we were, identical twins would be, well… identical. But they’re not. The slight differences between twins results from differences in how our environment interacts with our genes. (By environment, I’m not just talking about temperature and air quality, but rather all external influences). Our environment plays a big role in shaping the individuals we become, and our mothers have more effect on our environment than our fathers do. When we are developing in the womb, our moms’ bodies single-handedly provide us with nutrients, hormones, and antibodies (and sometimes pathogens). During this time, her circumstances and decisions will determine what kind of setting we are born into. After we’re born, the social interaction, nutrition, and antibodies (through breast feeding and/or vaccines) she provides will all influence our gene activity and thus how we develop. Collectively, the traits that we develop due to these factors and all mom’s other nongenetic influences are called maternal effects.

Mom gives us more genes, and has more input in determining how active each gene is. In the end, we are who we are in large part because of our moms.

So Mom, this is for you:

Happy (early) Mother’s Day!


Want to know more? Check these out:

1. BERNARDO, J. (1996). Maternal Effects in Animal Ecology Integrative and Comparative Biology, 36 (2), 83-105 DOI: 10.1093/icb/36.2.83

2. Wolf, J., & Wade, M.J. (2009). What are maternal effects (and what are they not)? Phil. Trans. R. Soc. B, 364, 1107-1115