Happy St. Patrick’s Day! If you are out and about looking for a four leaf clover on this auspicious day, keep in mind that the thing that makes them lucky is that they are hard to find.
A true four leaflet (a clover technically only has a simple leaf with multiple leaflets) clover is a four-leaved variation of the usually 3-leaflet white clover (Trifolum repens). Why is that so?
The current theory is that four leaflets are caused by a rare, naturally occurring recessive gene in combination with environmental factors. This can explain the rarity of “four leaf” clovers and why you sometimes find them in patches. The three leaflet version of the gene is so abundant that it is rare to find a clover without it. When you do, you’ll count yourself as lucky.
An example of how recessive and dominant genes function can be found in hair color. Since we are talking about all things Irish, let’s use haircolor, specifically red hair. The dominant form of the gene responsible is a protein that removes the reddish pigment from hair and skin. The recessive form is a non-functioning protein, therefore the red pigment builds up and causes red hair. It only takes one copy of the dominant gene from one parent to stop the red color from building up. To have red hair, you have to inherit the recessive gene for both of your copies of that gene. That’s why redheads are the most rare hair color.