Your genes code for all your traits. Some genes are dominant and expressed if you receive a copy from one parent. Others are recessive and only apparent if you receive a copy from both parents.
Genes are chains of molecules that tell your body to produce certain proteins. You can think of them as strips of code that make up a computer program. Except instead of a program, they provide the instructions for your distinguishing qualities, called traits.
You have about 20,000
Genetics can be very complicated. Many traits and diseases develop due to a complex interaction between many genes, and many of these complex interactions are still not fully understood by scientists and medical professionals.
Read on to learn about some traits and diseases that develop due to dominant and recessive genes.
Genes are called dominant when they’re expressed when you only have one copy from your parents. In contrast, recessive genes require a copy from both parents to be expressed.
Probably the most common example of a dominant gene is brown eye color.
Brown eye genes are dominant over blue eye genes. If you receive a brown eye gene from one of your parents, you’ll have brown eyes, too. However, it’s possible to have blue eyes even if both parents have brown eyes, if both parents have a blue eye gene that isn’t being expressed in them.
Many other traits are thought to be related to dominant genes. They include the following.
Interlocking fingers
Try interlocking your hands in front of you with one of your thumbs on top of the other. Is your left or right thumb on top? The tendency to put your left thumb on top is determined by a dominant gene.
Ear lobes
Some people have ear lobes that attach directly to the side of their face, while others have “free” earlobes that hang down without touching their face.
If your earlobes are free, you have a dominant allele for this trait.
Dimples
Having dimples is often considered a dominant trait. But as mentioned earlier, genetics can be complicated, and dimples are one example of this.
Dimples are considered an “irregular” dominant trait since it’s thought that other genes may also influence their development.
Widow’s peak
A widow’s peak is when your hairline comes to a point in your forehead instead of being straight across. It’s thought that having a widow’s peak is determined by a dominant allele.
Tongue curling
Being able to roll your tongue has long been thought to be a dominant trait, but now it’s thought that environmental factors may also play a role since some identical twins can roll their tongue while others can’t.
Freckles
Freckles are primarily determined by a gene called MC1R. The presence of freckles tends to be a dominant trait, but other genes and environmental factors (like sun exposure) may determine the appearance and pattern of freckles.
PTC tasting
Some foods, like broccoli and Brussels sprouts, contain a compound called PTC. About 75% of people perceive this compound as bitter tasting, but it’s tasteless for other people. PTC tasting bitter is thought to be a dominant allele.
Diseases
Many genetic diseases are linked to dominant genes. Some examples include:
- Hypertrophic cardiomyopathy: Hypertrophic cardiomyopathy is a heart condition almost always caused by a
single dominant gene . - Marfan syndrome: Marfan syndrome is a connective tissue disorder caused by dominant genes and affects about
1 in 3,000 to 5,000 people. - Hereditary long QT syndrome:
Most cases of hereditary long QT syndrome are linked to dominant genes. - Familial hypercholesterolemia: Familial hypercholesterolemia is genetically linked high cholesterol. It’s linked to certain dominant
genes like APOB, LDLR, and PCSK9.
Recessive genes require a gene from both parents to be expressed (appear visibly). For example, you require a blue-eyed gene from both parents to have blue eyes.
Other traits that are linked to recessive genes include:
- right thumb on top when interlocking your hands
- earlobes directly attached to your face
- straight hairline
- lacking dimples
- not being able to roll your tongue
- not having freckles
- not being able to taste PTC
As with dominant genes, some recessive genes are also linked to certain diseases. For example, sickle cell anemia is a recessive disorder that’s most common among African Americans
Here’s an example of how dominant and recessive genes interact using eye color. If your parents both have brown eyes, they can either have one or two brown eye genes and zero or one blue eye gene.
Here are the four possible combinations of genes you might receive if both your parents have brown eyes, and how your eye color will be expressed.
| Brown gene / brown gene = brown eyes | Blue gene / brown gene = brown eyes |
| Brown gene / blue gene = brown eyes | Blue gene / blue gene = blue eyes |
If one parent has blue eyes, they must have two blue-eyed genes. Your brown-eyed parent may have two brown eye genes or one brown-eyes and one blue-eyed. You may end up with:
| Brown gene / blue gene = brown eyes | Blue gene/ blue gene = blue eyes |
If both your parents have blue eyes, you will have blue eyes, too, since they both need to pass a blue-eyed gene to you.
Doctors may consider your traits if they suspect certain conditions, especially if you have clusters of physical or mental traits characteristic of a certain disease. For example, being tall and slender with very long fingers and toes can be a sign of Marfan syndrome. Knowing you have this condition can help your doctor understand if you’re at risk of any conditions linked to this genetic disease.
Genes are also thought to determine
Many traits are determined by recessive and dominant genes that you receive from your parents. You only need one copy of a dominant gene to express a certain trait, but you require two copies of a recessive gene.
Genetics can be complicated, and many traits and diseases develop due to a complicated interaction between many genes. Many of these interactions aren’t yet fully understood.