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How Do Four-Leaf Clovers Exist?

—Houston, Texas

Four-leaf clovers have many associations around the world, but they are mainly known for bringing good luck because of their rarity. This iconic symbol of luck appears every 1 in 5,000 clovers, due to a genetic mutation.

Four-leaf clovers are polyploids, which have extra copies of every gene. More specifically, these clovers are called allotetraploids because they have four copies of each gene. Tetraploid organisms either occur when cells undergoing meiosis repeat a phase more than once, resulting in gametes that have additional genes, or have abnormal cell division during mitosis that creates more chromosomes within their body cells. These extra genes are then expressed, producing an additional leaf in a clover.

allotetraploid, chromosome mutation, meiosis, genetics, four-leaf clovers
Chromosomal mutation during meiosis that causes allotetraploids

Four-leaf clovers are rare to find because the mutation is caused by a recessive gene in clovers. They are created by crossing two heterozygous three-leaf clovers where each have one dominant allele that codes for the three-leaf gene and a recessive allele that codes for four leaves. Dominant alleles mask the recessive gene, so the dominant gene is shown in three-leaf clovers. Using a Punnett Square that identifies the frequency of gene expression, the heterozygous clover parents can be represented by Cc (C symbolizes the dominant gene and c as the recessive gene). Once they are crossed, it results in the clover offspring having a 25% chance of becoming homozygous dominant (CC), 50% chance of being heterozygous (Cc), and 25% chance of being homozygous recessive (cc). Homozygous recessive offspring are four-leaf clovers because there is no dominant three leaf gene present. Therefore, there is a 25% chance that a four-leaf clover is made from two heterozygous clovers.

Four leaf clovers, Three leaf clovers, Punnett Square, heterozygous, homozygous, genetics
Crossing of two heterozygous clovers using the Punnett Square

Having four leaves can be an advantage: the four-leaf clover is able to absorb more sunlight as it has a higher amount of chlorophyll within the additional leaf compared to the three-leaf clover. Furthermore, it increases the chance of the clover’s survival because of its increased access to sunlight and it can risk losing more leaves than a three-leaf clover. However, four leaves results in more surface area, which makes the four-leaf clover have excess pores. Having additional pores results in more water evaporating through their leaves.

While four-leaf clovers occur rarely in nature, it is possible for clovers to have more than four leaves, which are extremely rare. However, it is considered that the more leaves you find on a clover, the luckier you are.

Increase your luck by finding these STEM·E events!

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