He’s got Mama’s eyes, Daddy’s smile and Aunt Edna’s earlobes. She’s got Grandpa’s button nose and looks just like you did as a baby. They’re just so beautiful that you sometimes wonder how in the world you created such a miracle. You might also wonder how your son got red hair when his parents are both brunettes, or if he’ll even keep his hair since all the men in your family are balding. Or if your daughter will be a sweet soprano like you or wind up tone deaf like her father.
Although scientists have decoded the human genome (the three billion "letters" or chemical building blocks that make up human genetic material), modern science is still years away from clearly understanding parental inheritance. Since doctors are first attempting to identify the genes that cause illnesses like cancer and Parkinson’s disease, the genes for eye color and athletic ability will remain a mystery for a while longer. But we’re not completely in the dark; and with the information we already know, we can make some pretty good guesses about our future NFL quarterbacks and Mozarts.
Most cells in the body contain 46 chromosomes, but Dad’s sperm and Mom’s egg each contain just 23 chromosomes. When egg meets sperm, they join to form the 46 chromosomes of a single cell that will rapidly divide until it becomes the approximately 100 trillion squirming cells that you lovingly diaper, feed and babble to all day.
Each chromosome carries many genes, which also come in pairs. Since half of your baby’s genes come from mommy and the other half are from daddy, the probability of a baby getting any particular gene is similar to the probability of flipping a coin. Sounds like predicting the possible combinations that make up your baby’s looks and personality should be easy, right? No such luck. Only a few traits, such as blood type, are controlled by a single gene pair. Most traits, like skin color, hair color and height are the result of lots of genes working together, many of which are still unidentified.
Blue, Green, and In Between
“We know some factors influencing human pigmentation, including skin and eye color, but we definitely don't understand this fully,” says Dr. Kathryn E. Beauregard, PhD, and deputy editor of The American Journal of Human Genetics. So can you predict eye color? Not exactly, but you can get close. Light-colored eyes like blue, gray and green are recessive and more likely to show up when both parents have light eyes and less likely to appear when one or both parents has brown eyes. But it is possible for two brown-eyed parents to have a blue-eyed child if the genetics are right.
Hair color follows the same basic principles as eye color. The degrees of darkness depend on the amount of melanin produced, with genes for less melanin (or lighter hair) being recessive and darker hair being dominant. What about those fiery redheads? Red hair results from a special recessive gene for red hair. When combined with genes for brown or black hair, the red gene is obscured and often goes unnoticed. But combined with genes for lighter hair shades, and you get strawberry blonds, light auburns and flaming orange carrot tops.
What about those with no hair at all? One popular misconception is that the mother’s side of the family passes along the gene for male pattern baldness. This belief has had men monitoring the scalps of their maternal grandfathers and uncles for years. In truth, baldness is a complicated genetic trait that can be inherited by either the mother, the father or both. So don’t blame your mom for hair loss!