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!
Thoroughbred Jockey or Pro Wrestler
Height is another complicated trait that’s influenced not only by a child’s genetic makeup, but also by outside forces like health and nutrition. Gender plays a role as well, since boys tend to grow taller than girls. Scientists approximate that genetics and gender count for about 70 percent our height, while 30 percent is determined by environmental factors such as diet, exercise and overall health. Popeye was right when he extolled the virtues of spinach! Humans have been growing steadily taller over the centuries as our nutrition and health care improve.
For a fun and fairly accurate method to determine your baby’s adult height, add the parents’ heights together, divide by two, then add 3 inches for a boy or subtract 3 inches for a girl. While this method is relatively good, your child’s ultimate height can vary by as much as 5 inches above or below this calculation.
Mozart to Manilow
Although specific genes affecting musical ability have yet to be identified, there is undoubtedly a link between musical ability and heredity. In most cases, great musical talent shows up at a very young age, and great musicians usually have parents or close relatives with similar talent. But genes can’t do it alone. A child who inherits “musical genes” will rarely exhibit any talent without environmental stimulus like music played in the house, singing lessons or early exposure to musical instruments. The University of California San Francisco is currently conducting a study of people with perfect pitch. Their research shows that 40 percent of children who begin formal musical training by age four develop perfect pitch. In contrast, only four percent of those who began training after age nine did.
On the other hand, a person can be trained and coached to become a solid musician, but without the right DNA, will never become a virtuoso. UCSF scientists found that musicians with perfect pitch were four times more likely to report a family member with perfect pitch than those without it.
Smart Alecs and Alices
Like musical ability, research indicates that intelligence has both biological and environmental bases, but that genetics play a powerful role in intelligence potential. Studies show that the IQ difference between identical twins (even those raised in different homes) is miniscule (5.9 points), and many research studies indicate the more closely related two people are, the more similar their IQ’s are likely to be.
Although genetics have a lot to do with intelligence levels, environment has a lot to do with how those innate smarts actually develop. For example, a challenging environment may boost your IQ, but your score could drop again if your environment changes. Researchers in Canada found that baby rats whose mothers gave them more attention learned more easily, while doctors at UT Southwestern Medical Center at Dallas say spending time with your children, reading to them, playing games and otherwise showing you care not only makes your children feel good, but it could help them be smarter.
What about so called “genius genes”? Science sees genius as a rare combination of superior genes, which may not even require a high level education to flourish. Two of history’s greatest minds, Leonardo de Vinci (sculptor, mathematician, engineer, artist, musician and poet) and William Shakespeare came from obscure backgrounds and had very little formal education. Despite lack of flashcards and preschool classes, both displayed dazzling intelligence and talent from the time they were young children.
Walk This Way
Although your little miss might stand with her hands on her hips and her head cocked to the side just like mom, scientists believe that characteristic movements of the hands and mouth or ways of walking and moving are learned behaviors, much like languages or accents. Just as you’ll notice sisters or families who move or speak the same way, you’ll see the same similarities among groups of unrelated policemen, farmers, actresses or newscasters. Since children consciously and unconsciously mimic their parents and relatives, we see the same mannerisms in families, but they aren’t genetically inherited.
However babies do come into the world with a set of inherited behavior patterns such as the way they feed themselves (raking first, then using pincer grasp), move, grab at objects, smile, babble, roll over and sit up. But from the moment of birth, they begin to be trained and influenced by parents, caregivers, siblings, friends and teachers. So how much of personality is nature and how much is nurture? Dr. Beauregard says, “We’re not sure, but we’re working on it.” We’ll have to wait a few years or decades to get a definitive answer, however studies show that babies who are particularly good natured, sensitive or aggressive tend to have the same personality traits later in life. The bottom line: each kid is different, so don’t push your expectations upon them — instead love them for the unique and special individuals they are.
Did You Know?
- For every 100 girls born, there will be close to 106 boys? Why? Males are the weaker sex, and the death rate in almost every stage of life is higher for males. So we need more boys to begin with!
- Heredity plays a small role in creating twins. Although a gene for twinning hasn’t been identified, the gene for hyperovulation is passed from mother to child. The sister of a woman who has twins has twice the average chance of having twins too.
- Thirty percent of identical twins exhibit mirror-imaging. That’s when a birthmark, feature or oddity appears on the right side of one twin and the left side of the other. This happens when the single embryo from which they were formed splits like two halves of an apple.
- Speaking of twins: who’s most likely to have them? People of African descent. African Americans have a rate of one twin pair in 73 births, and the Yoruba tribe in Africa sees one set of twins in every 30 births!
- Good news for flat-chested women; your daughters may not be doomed to endure the teasing you got in junior high. The genes for breast size and shape come from both the mother and the father’s side of the family.
- Big eyes are dominant over small ones, prominent noses dominate button noses, dimples and cleft chins are more common than smooth faces, thick lips beat out thin ones and, good news, long lashes are dominant too. Curly hair is dominant over straight unless one of the parents is of Asian descent. Asians have a unique straight hair gene that tends to dominate all the others.
- Who knew? Quirky physical features such as widow’s peaks, cleft chins and gapped front teeth are almost always dominant. Why don’t we see them more often? They tend to show up in varying degrees and may not be immediately noticeable. Also, extensive use of orthodontic braces and hair coloring in our society keeps the traits hidden to observers.
- Do you suffer from the ACHOO Syndrome? ACHOO (Autosomal Dominant Compelling Helio-Ophthalmic Outburst) sufferers automatically sneeze when they look at the sun or bright lights. Twenty to 30 percent of the population (the author included) suffers from this amusing malady. Geneticists claim that the syndrome is dominant, runs in families, and the number of sneezes routinely produced is also genetically determined. God bless you!