Wednesday, June 19, 2013

Thanks Dad!

Daddy's girl. Photo from
Let’s take a moment to appreciate just how special dads are. Across the animal kingdom, fathers caring for their young is the exception, not the rule. Paternal care is most often seen in species in which males can be pretty sure that they are indeed the father (for example, in species that fertilize eggs outside of the mothers’ bodies or in socially monogamous species). Mammals rarely act fatherly - Only 10% of mammalian species show paternal care at all. But among mammals, primates (including ourselves) are more likely to do so.

Dads do a number of things to care for their young: Depending on the species (and the individual), they may incubate them, provide them with food, groom them, keep them close to home, guard and protect them, and help them gain survival and mate-attraction skills. These behaviors are costly to a male, who could often be reproductively more successful by spending his time and resources courting more females. But they do it nonetheless.

Regardless of whether a dad is behaviorally involved with his offspring, he contributes a fair amount to the individuals we grow up to be. Dads provide nearly half of our genes, which are the instructions for the production of all of our bodies’ tissues and chemicals. These tissues and chemicals don’t just make up our physical bodies, they underlie much of our physical abilities, susceptibilities to disease, and behavior patterns (including personalities).

Just because about half of your genes are from dad and about half of your genes are from mom, doesn’t mean that you are strictly half-your-dad and half-your-mom. Imagine you are given two books of Thanksgiving Day recipes: Both books have the same recipe for turkey, so that is the one you are going to follow. But one book has a recipe for garlic mashed potatoes and the other has a recipe for plain mashed potatoes. If no one in your family likes garlic, you will likely follow the recipe for plain potatoes. In addition to choosing between recipes, you can also combine them: If one book has a recipe for stuffing with lots of garlic and onions and the other has a recipe for stuffing without garlic or onions, you could make stuffing with onions and no garlic. Your pairs of genes work in similar ways: if the two copies of a gene are different, you may get the trait of one of them or they could combine to give you an intermediate trait. If the versions of the gene are the same, you will likely just get that trait.

When something is made by following the instructions in a gene, this process is called gene expression. Not all genes are expressed equally everywhere: All of the cells of our body have the same genes, but the way they express in a particular cell determines whether that cell is part of a lung, a heart, a brain or something else. If for a particular gene the instructions in the gene from one parent are followed and the gene from the other parent is ignored, this is called parent-specific gene expression. We have several traits that occur as a result of dad-specific gene expression.

Your genes are lined up on doubled-stranded DNA, which is tightly coiled around proteins called histones. The DNA is then wrapped even more and packed into chromosomes. You have 23 different pairs of chromosomes in each cell, where one of each pair came from mom and the other came from dad.  Figure adapted from an image by KES47 at Wikimedia.
More variation is caused by the fact that two individuals with identical genes may not have identical traits. Our genes are encoded in strings of DNA, which are coiled around proteins called histones and then packed into chromosomes. Biological factors can cause the string of DNA to coil tightly around these histones, hindering access to any genes in that section of DNA. This reduces or even prevents gene expression from happening (Imagine what would happen if two pages of your Thanksgiving Day recipe book stuck together). Alternatively, other biological factors can relax the DNA string, increasing gene expression. Gene expression is often decreased or increased as a result of life experiences (such as social experiences, nutrition, or exposure to drugs and toxins). If a particular gene is decreased or increased this way in a sperm or egg cell, this effect can be passed on to the children (and often grandchildren and great-grandchildren and so on). This process of inheritance that is not a strict passing on of genes is called epigenetics. Epigenetics is a new and emerging field, but we have already learned that mothers that provide more parental care create lasting changes in their offspring that are passed down for multiple generations. It is likely that fatherly care has a similar effect. We also know that a father’s nutrition and exposure to drugs and toxins can pass several traits down the generational line through epigenetics.

Dads play a special role in the individuals we become. Their behavior with us, genetic makeup, and even personal experiences shape our physical appearances, health, abilities and personalities. If you haven’t yet, take a minute to say “Thanks, Dad!”

Happy (late) Father’s Day, Dad!

Want to know more? Check these out:

1. Curley, J., Mashoodh, R., & Champagne, F. (2011). Epigenetics and the origins of paternal effects Hormones and Behavior, 59 (3), 306-314 DOI: 10.1016/j.yhbeh.2010.06.018

2. Wilkins, J., & Haig, D. (2003). What good is genomic imprinting: the function of parent-specific gene expression Nature Reviews Genetics, 4 (5), 359-368 DOI: 10.1038/nrg1062

And a special thanks to Tony Auger, Cathy Auger, Stacey Kigar, and Robin Forbes-Lorman for their feedback.

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