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How come some clovers are three-leafed and some are four-leafed?
Answer 1:

The number of leaves on a clover is controlled by the genes of a plant. If you don't know what genes are, think of them as the information storage center. Genes tell the plant how many three leaf and how many four leaf clovers to produce. If you want to learn more about how this happens, look up genes in an encyclopedia and it will tell you all about how genes work. Also, Scienceline just answered a question about genes and how they work to control flower color, so it should be on our Scienceline webpage database. Check it out!

So, back to your question. Clovers are a type of plant right? Clovers have some stems that have three leaves and a few that have four leaves. Generally speaking, the number of three leaf clovers for every four leaf clover is probably 100 to 1. That may be why four leaf clovers are considered good luck by the irish; because they were so rare. These days, however, plant biologists have been breeding clover plants that produce a large number of four leaf clovers. So these days it is easier to find four leaf clover plants. You can even order them online if you want (of course, ask your parent or parents first). Or, ask your parent or parents to take a trip to a nursery (where they sell plants) and ask if they have clover plants. You may find that the ones they sell have many more four leaf clovers than those in your yard or school grounds. Let us know what you find out, ok?

Answer 2:

I am not sure exactly what the mechanism is that produces a 4-leafed clover, but I am assuming it is due to genetic variation within a clover field. I would guess that it is either that a 4-leafed clover is produced by a genetic mutation or because the genes that produce a 4-leafed clover are recessive to the genes that produce a 3-leafed clover. You've probably studied about genes in your science class before, so you might already know about recessive and dominant genes (or alleles). For example, eye color in humans is a common phenotype in which to observe genetic variation. If you look around your class, how many people have brown eyes, how many have green eyes, and how many have blue eyes? You'll probably find that most people have brown eyes, some have green eyes and even fewer have blue eyes. That is because blue eyes are a recessive phenotype. A phenotype is the result of a particular gene that you can observe or measure. So it may be that a 3-leafed clover is the dominant phenotype relative to the recessive 4-leafed clover phenotype. Assume there are two alleles (two copies of the gene) that code for # of leaves in a clover. Let's call the 3-leafed coding allele "G", then we'll call the 4-leafed coding allele "g". Notice how I gave them the same letter (because these 2 alleles combine to code for one phenotype)and that I gave the dominant allele (3-leafed) a capital letter and the recessive allele (4-leafed) a lower case letter. One allele comes from the "father" clover and the other allele comes from the "mother" clover to produce a seed that grows into a new clover. If the mother's genotype (or allele combination) was Gg she would have 3 leaves (because the big G "wins out" or is dominant over the little g). The father's genotype was also Gg and "he" was also 3-leafed. These two parents can produce 3 different genotypes if their alleles split and recombine into all the possible combinations. Draw a box with 4 squares and in each square write one of the alleles from the "mother" in the top row, then do the same for the "fathers" alleles in the second row. You'll have a punnet square or box that looks like this:
G g
G g
Now write the four possibilities that could result from all the possible combinations of these 4 alleles. You can do this by reading the box first just looking at the left column, that would produce a genotype = "GG", which would result in a phenotype or a new "baby" clover with 3 leaves. Then read the box on the right column going down, producing a genotype = "gg", which would result in a phenotype or a new "baby" clover with 4 leaves. Then read the box diagonally one way, then diagonally the other way and you'll find both of these produce a genotype = "Gg" (the order doesn't matter, "Gg" = "gG"). This genotype would result in a new baby clover with 3 leaves also. Notice how both "Gg" and "GG" both produce 3-leafed clovers, but only "gg" produces a 4-leafed clover. That is because whenever there is a "G" present it will dominate over a little "g" and the result will be a three leafed clover. Notice how a 3-leafed clover is 3 times as likely to occur as a 4-leafed clover just looking at the possibilities that can result from this type of parental cross.
Well, that is a long-winded answer to a seemingly simple question, isn't it! One thing you could try is finding a field of clovers and counting the number of clovers that are 4-leafed and the number of clovers that are 3-leafed. This may help you understand the genetics that result in the 4-leafed clover variety.

Answer 3:

I have often wondered about this very question! Did you search for some four-leaf clovers this past weekend over St. Patrick's Day?

I found this story on the web by a lady named Catherine Yronwode. While Catherine is not a scientist by profession, she did make some shrewd observations based on her own experiences with clover, and then came up with one possible hypothesis for what she had observed (different frequencies of 3 versus 4-leaf clover plants). See if you can figure out what her hypothesis is in the following passage:

"...I realized that for folks who live in town, four-leaf clovers are a real rarity, rare beyond what they are for the rest of us. I have a couple of patches on my "lawn" (well, it's a green area, so I call it a lawn) where four-leaf clovers occur with much higher frequency than elsewhere. It's gotta be a genetic variation, like multi-toed cats and six-fingered humans.
When little kids visit, they like to search for four-leaf clovers. A few grown-ups do too. They've got to have sharp eyes to find them. Sharper than mine, anyway. Personally, I have only found one four-leaf clover on this property, and one a long time ago, in Santa Monica, when I was about eight years old..."

FROM http://www.luckymojo.com/clover.html
copyright 1995-2000 catherine yronwode

As you probably discovered by reading this paragraph, Catherine's hypothesis is that genetic variation is the cause of the rare occurrence of 4-leaf clovers relative to 3-leaf clovers. Now, as you know, a hypothesis is not a scientific fact, but it is a good speculation based on direct observations. A hypothesis is a statement that is testable in order to know if it is true or false. In other words, if you have a hypothesis, the only way to know if it is true or not, is to try to test it somehow!

Scientists have done tests with Trifolium repens (scientific name for white clover, a common North American weed) and found out a lot about recessive and dominant genes that give rise to phenotypic traits (traits that we can see such as 4 or 3 leaves, long or short stems, etc.) Within the DNA of the cells of the plant, the gene or genes are code for 4 leaves and not 3 leaves are recessive (do you know what recessive and dominant traits are?). This is why they only occur very very rarely in nature. Some pages on the Internet lead me to believe that people can now genetically engineer 4-leaf clovers, but the most prized specimens (for house plants and jewelry making!) are still those rare ones that people find growing naturally among the thousands of dominant-trait 3-leaf clovers.

**Now here is my question to you: do you think there is an advantage to having 4 leaves versus 3 for a plant? If you think there might be an advantage, (an "evolutionary advantage", as scientists would call it!) then do you think that over lots of time, the 4-leaf clovers would become more common than 3-leaf clovers? Send me back your hypothesis! How could we scientifically test this, do you think? Got any ideas? **

Here is some other information I found on the Internet about white clover that might interest you:

Scientific Name: Trifolium repens

Common Name: white clover

Range: throughout United States, except Great Plains and extreme South; found in lawns, fields, roadsides, and disturbed habitats

Origin: native to Eastern Mediterranean and Asia

Botanical description: White clover is a perennial plant with alternate compound leaves found in threes. The dark green leaves often have a white "V" or crescent in their center.
The flowers are white, sometimes tinged with pink, and are actually dense groups of individual red clover by this close to the ground growth pattern and, of course, the white flowers when flowerettes arranged in a round head. The plant grows close to the ground and is notorious for its ability to creep, or spread, by the use of stolons. White clover is most easily distinguished from blooming. Red clover plants often have larger leaves than those of white clover.

What's in a name: Like red clover, white clover's genus name, Trifolium, means "three leaves", and its species name, repens, means "to creep".

All in the family: White clover is a member of the Leguminosae family, which includes red clover and other plants such as peas, beans and peanuts that are nitrogen fixers (see description in red clover information sheet).

Cultural uses: White clover blossoms were used in folk medicine against gout, rheumatism, and leucorrhea. It was also believed that the texture of fingernails and toenails would improve after drinking clover blossom tea. Native Americans used whole clover plants in salads, and made a white clover leaf tea for coughs and colds. White clover is thought to clean

Answer 4:

Leaf number in clovers is genetically determined. Occasionally a mutation can occur in a member a three-leaf clover population that results in a clover of the following generation developing four leaves. Because of the overall rarity of such events in a "normal" environment and the nature of its heredity, usually the trait of "four-leafness" does not become fixed in the population. This, however, does not apply to a habitat exposed to mutagenic or carcinogenic substances where the increased rate of mutation can be quite high and possibly increase the frequency of "four-leafness" in future generations. In a neighborhood where I once lived, one of the houses on the street had a small patch of clover growing near the sidewalk in their front yard that consisted entirely of four-leaf clovers. The ironic thing about this family is that were consistently "unlucky". I guess that one can get too much of a good thing.

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