Genetics is so interesting—it can contribute to some siblings who look nearly identical, while others make you question if they’re even related. In this guide, we’ll walk through how genetics can impact some of your child’s physical traits.
By Shannon Wieloch, Genome Medical
Decoding the genetic code
Think of your genetic information like a series of books (larger than the seven books in Harry Potter yet smaller than the 75 issues of The Sandman).
Everyone should have two copies of each book (chromosome). Each book has thousands of words (genes) in it. These genes work together to tell a story, basically, a story of you.
Sometimes words are misspelled, i.e., genes have variants. This can cause a gene to not work the way it should and lead to a person having a genetic disease. An example is inheriting a variant in the CFTR gene from your mother and inheriting another CFTR variant from your father, which could result in you having cystic fibrosis. There are a lot of genes in which, if you have a variant (or two), you have a genetic disease.
Other genes can have variants that allow them to still work. These variants don’t cause a genetic disease, but rather result in different features or traits. These are the ones we’ll be talking about below.
What eye color will my baby have?
Researchers used to think that eye color was determined by a single gene and followed a simple inheritance pattern in which brown eyes were dominant to blue eyes. This theory has since been debunked.
Most of the genes associated with eye color are involved in the production, transport, or storage of a pigment called melanin. Eye color is directly related to the amount and quality of melanin in the front layers of the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less of this pigment.
While two particular genes, OCA2 and HERC2, play a major role in determining eye color, several other genes play smaller, yet also important, roles. It is thought that the overall effects of these genes likely combine with those of OCA2 and HERC2 to produce a continuum of eye colors in different people.
So to answer the question of what eye color you can expect your baby to have...the simple answer is that there is no easy answer because so many genes are involved.
How tall will my child be?
Several formulas exist to estimate your child’s adult height. For example:
- Add the mother's height and the father's height in either inches or centimeters.
- Add five inches (13 centimeters) for boys or subtract five inches (13 centimeters) for girls.
- Divide by two.
Another proposed method to estimate a child's adult height is to double a boy's height at age two or a girl's height at age 18 months.
While the general theory is that two tall people will likely have tall children, while two shorter people will have shorter children, this isn’t always the case. Height is impacted by multiple genetic and environmental factors, including nutrition, sleep habits, mental health, medical conditions, and exercise.
What hair color will my baby have?
Admittedly, this genetic counselor’s hair color comes out of a bottle. But biologically speaking, hair color, like eye color, is determined by the amount of melanin present. An abundance of one type of melanin, called eumelanin, gives people black or brown hair. An abundance of another pigment, called pheomelanin, gives people red hair.
As expected from what was written about eye color above, multiple genes play multiple roles in determining one’s hair color. Most of these genes are involved in the production of melanin in hair.
While hair color is difficult to predict, we do know that the majority of redheads have a genetic variant in the MC1R gene. However, a parent may not know they carry this variant unless they themselves have red hair, thus keeping the hair color of their children largely unpredictable.
Will my child inherit my dimples?
A dimple is a small indentation found on one’s skin that is caused by a difference in the formation of the underlying muscle.
While we can define what a dimple is, little research has been done into the actual genetics of cheek dimples so, simply put, scientists don’t know if dimples are inherited or not. Cheek dimples may be inherited as an irregular dominant trait. A dominant genetic trait means that one copy of a genetic variant in a set of genes is enough to cause dimples. But because the inheritance pattern of cheek dimples can be unpredictable, inheritance is stated to be irregular dominant. In addition, it is unclear if dimple inheritance is caused by a single set of genes. Multiple genes could actually influence cheek dimples.
What are the chances my child is left or right handed?
Approximately 10 % of the human population is left handed, and like many aspects of human development, handedness is complex. This means that it is influenced by multiple factors, including genetics, prenatal environment, cultural influences, and chance.
Though a recent study has focused on four genetic regions associated with left-handedness, other studies have suggested that up to 40 genes may contribute to this trait.
The bottom line: a lot of left-handed parents have left-handed children...and right-handed children. Just as a lot of right-handed parents have right-handed children...and left-handed children.
True or false: baby will look like the father
As a general rule, any baby will inherit approximately 50% of their genetic material from their mother and 50% from their father. Yet, as the genetic material in our bodies is not organized by body part or system, babies do not receive a complete package of “eye” genetic information from one parent or “nose” genetic information from another.
Regarding the thought that a baby will look like the father, let’s hope that’s true...to a point. But current studies seem to think that this theory is related to an evolutionary advantage—that fathers seeing themselves in their offspring leads to greater bonding and a larger desire to care for said baby, thus perpetuating their genetic lineage.
If you are wondering what color hair and eyes your baby will have or how tall she or he will be, the answer is, we largely don’t know.
As a genetic counselor, we don't often talk to patients about the inheritance of traits, as we tend to focus on the inheritance of genetic diseases, such as cystic fibrosis, Fragile X syndrome, and Huntington’s disease. The impact of these diseases can be profound, and our job is to help families understand their risks and educate them on the availability of testing options and resources related to these diseases.
Unlike the inheritance of many genetic diseases, most genetic traits, including hair color, eye color, and height, have a more complicated inheritance pattern. This is because many genetic diseases have a single set of genes that are related to them, while genetic traits have a multitude of genes that interact in any number of ways to result in different outcomes. But not knowing only adds to the excitement of finding out who your baby is, inside and out, as they grow and develop into their own little person.