If you think back to high school biology, you probably remember something learning a bit about genetics (maybe you can even recall the old โPunnett squareโ!). Thatโs when weโre taught that DNA accounts for things like genes tied to blue eyes, red hair, etc. (Remember, genes are segments of DNA and theyโre also contained in our chromosomes.)
Today isnโt going to be a science lesson, donโt worry, but it is going to be interesting.
Just remember, there are two main categories of genes: dominant and recessive. Dominant genes can โoverruleโ recessive genes.
Generally speaking, you need two genes (one from your mother and one from your father) to get a trait, like eye color. One dominant-style gene means thatโs the trait youโll get. So when it comes to, say, brown eyes (a dominant trait), no matter what other color you inherit from your other parent, the gene for brown eyes is going to win. Blue-eyed dad and brown-eyed mom? Youโre getting brown eyes.
When a gene is recessive, you need two of the same kind to get a recessive trait, like blue eyes. In this case, to be blue-eyed means both of your parents should have blue eyes (of course, there are lots of little details involved, so donโt necessarily have to run out and buy a DNA test).
Whatโs really interesting here is that while common sense would tell us that dominant genes should be more prevalent in our population, but thatโs not always the case. Most people donโt know is that recessive genes can be really common.
What all that said, letโs prove it.
Here are some genetic traits that are common, even though they require 2 recessive genes (which makes them statistically unlikely):
1. Colorblindness
Colorblindness is surprisingly common, especially in men.
The gene for colorblindness lies on the โXโ chromosome (explaining why it more often affects males โ being female means you only have one X chromosome).
Oddly enough, even though this recessive trait is an evolutionary disadvantage, it currently impacts 8% of men!
2. Straight hair
Straight hair is actually a recessive trait!
There are two gene options when it comes to hair, curly and straight. But as we all know, however, there are lots of different hair types, not just 2.
Hair is actually a special case because the hair gene has โincomplete dominance.โ That means you can get a blend โ so a curly-haired mother and a straight-haired father would likely get a child with wavy hair (somewhere in between).
3. Hairless hands
Ok, this one is more straightforward.
If you look at a section of your fingers, the section before it hits your hand, you may or may not have hair. If itโs bare, you have the recessive trait associated with it!
Itโs known as the โmid-digital hairโ gene โ fun, right?
4. Blue eyes
As we know, blue eyes are recessive. It depends on two blue-eyed genes being inherited, one from each parent.
That means it really shouldnโt be as common as it is.
(But unlike what we learned in biology, eye color is actually an expression of quite a few different genes, not just one. So thatโs why you get green eyes or even a blue-eyed child coming from a brown-eyed parent, on some occasions).
5. Not being nearsighted
Nearsightedness is very common and itโs estimated that 1/3 of people have the condition.
Yet, itโs a recessive trait, so itโs surprising that so many people experience it!
(But youโre probably now realizing that when this happens, it means other genes and environmental factors are affecting the trait as well.)
6. Tone deafness
Have trouble staying on pitch? Known as being tone-deaf, itโs something we think of as an insult, not necessarily a family characteristic.
But being able to carry a tune is a recessive trait! That means if you canโt hear how bad you are, you can just blame it on your genes.
7. Type O blood
Blood type is a really great example of genes in action. You get your blood type from how your parentโs genes interact. Type O blood, the most common type, should be dominant if itโs so common, right? Wrong! Itโs actually recessive.
8. Height
Shortness is a dominant trait, although itโs not as simple as a single gene. There are thousands of genes that make up your height trait, but the one that makes you tall is recessive.
So youโre likely to have two tall parents if youโre tall.
9. Clear skin
This isnโt about acne, itโs about freckles! Having a โnon-freckledโ face is actually about how much skin damage you have, but your ability to get freckles from sun damage is recessive. Odd since so many people have them.
10. Poison ivy reaction
Some people are actually immune to poison ivy! And the trait is dominant!
It makes you wonder why 85% of the population isnโt immune to it. Kind of annoying, right?
11. Dwarfism
Dwarfism, the trait that results in a smaller human with short, compact features, is actually a dominant train. Just because someone has dwarfism, however, doesnโt mean their parents do.
All that means that anyone who doesnโt have dwarfism has a recessive trait.
12. Streaky white hair
A streak of white hair isnโt all that common, even though itโs a dominant trait.
For anyone out there without those streaks, it means you have a recessive gene responsible for it!
13. Being double-jointed
Although itโs commonly referred to as being โdouble-jointedโ itโs not actually called that โ itโs called joint hypermobility.
Thatโs actually a dominant gene, but only a quarter of people in the US express it, meaning 75% of people have the recessive trait.
14. Non-fused fingers
Donโt have fused fingers? Thank your recessive trait!
The gene that works to fuse or โwebโ fingers is actually a dominant one, albeit a rare one.
15. Being 5-fingered
Have โnormalโ hands? That just means you are expressing a recessive gene trait thatโs rather common!
To have more fingers is actually a dominant trait, but it is clearly not as predominant.
We often think that recessive = rare, but that isnโt the case!
One look at your hands is a great way to show that isnโt true (as long as you donโt have more than five fingers, that is)!
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