It’s enjoyable to make assumptions about your unborn child’s appearance when you’re pregnant. How will their hair appear? Will they have brown or blue eyes? Although parents can’t help but guess at the future, they can never be certain until the baby is born. According to Barry Starr, Ph.D., a geneticist in residence at The Tech Museum in San Jose, California, even if they looked at all of a fetus’ DNA, they still wouldn’t be able to properly foresee anything. It turns out there is a lot we don’t know about genes.
The Baby’s Hair Genes
Each person inherits many gene pairs that affect hair color (and each pair includes one gene from each parent). According to Michael Begleiter, who works as a genetic counselor at Children’s Mercy Hospitals and Clinics in Kansas City, Missouri, if a newborn receives ten pairs of genes in total, for instance, that means twenty distinct genes could have an impact on their hair. However, it is unknown how many genes are ultimately responsible for a person’s hair color. If a baby born to two brunettes had recessive blonde genes in addition to their dominant brown genes, only their light-colored genes were passed on.
The Baby’s Eyes
Although some newborns have bluish-gray eyes at birth, this can change as they develop. In actuality, unless a newborn has dark eyes at birth, their eyes will usually change. A baby’s eye color may not stabilize for as least six months. The iris’ color-producing cells must be exposed to light to become active.
At least two genes — one with brown and blue versions and the other with green and blue versions — influence the development of a person’s eye color. The combination of alleles that a child inherits from both parents determines the color of their eyes. A newborn is more likely to have dark eyes if one parent has dark eyes and the other parent has blue eyes. Because the brown gene is dominant, brown eyes will develop if a baby carries it. However, if both parents have recessive blue-eye genes, even two parents with brown eyes can give birth to a child with blue eyes.
The Baby’s Size
It’s challenging to foresee a baby’s size because a newborn’s measurements don’t always indicate their future height and weight. According to W. Gregory, a variety of factors, including the diet of the expectant parents and any medical issues like gestational diabetes, might affect the baby’s size at delivery. Family doctor Gregory Feero, M.D., Ph.D., is a special advisor to the National Institutes of Health’s National Human Genome Research Institute.