What The Freck is a Freckle?

I've had freckles all over my body for as long as I can remember- on my face, my arms, my legs, even my back. I always liked my freckles, and I thought they made me cool and unique because no one else had freckles that looked exactly the same as mine. I never really questioned what they were or how they came to be, since most other people in my family and around me also had freckles. I thought they just existed, that I've had them my entire life and it's just apart of my skin. But after having completed the AP Biology course and learning all sorts of different things about cells and the body, I've come to ask myself, what even is a freckle?

Person with freckles. 

What exactly is a freckle?

Freckles are small brown spots that are found on the surface of our skin, and are harmless. Freckles are actually a result of overproduction of melanin in the body, which is responsible for giving us our skin and hair pigmentation. Melanocytes are the cells that are responsible for producing the melanin within our bodies. Sometimes these melanocytes are more clustered together and can overproduce the amount of melanin they make, which leads to smaller, more centralized areas of melanin shown on our skin, which is what a freckle is!

Why do freckles exist?

If you've ever noticed that your freckles are more prominent in the summer than in the winter, there's a good explanation for that. Melanin production is affected by ultraviolet radiation, or UV rays, which come from the sun. Melanin protects the skin from harmful UV rays, as overexposure to UV radiation can cause extreme damage to the skin if the skin is not properly protected, which can lead to damage to the skin barrier and even skin cancer. The sun's UV rays are more powerful and harmful in the summer, which is why it's easier to get a sunburn when you're at the beach, and the reason why your freckles become darker in the summer. So although freckles are harmless, they still serve a purpose, being that they protect your skin from UV damage and make you look pretty unique too.

UV Rays and Melanocytes.

Do I have freckles because my parents have freckles?

Yes! While the appearance of freckles is affected by UV radiation exposure, they are also genetic too! The MC1R gene encodes for a protein called melanocortin 1 receptor. This receptor is responsible for the pigmentation of our skin. Since we inherit two copies of each gene from our mom and our dad, they pass down the phenotypes created from the alleles found on the genes. Having freckles is a dominant trait, so if you have freckles, at least both or one of your parents is homozygous dominant or heterozygous for the dominant allele on MC1R, which is why both you and your parents may have freckles. Then again, your parents may have freckles, but somehow you may not have any freckles at all, which is due to the possibility of both parents being heterozygous (Ff) for the freckle allele. This means that your parents had a 1/4 chance of having a child without freckles (ff), since not having freckles is a recessive trait. The allele for red hair can also be found on the MC1R gene, and is recessive.  It might be confusing that red hair is recessive while freckles are dominant, even though most people with red hair have freckles, but this is because we have two copies of each gene, and the whole process of freckles appearing is the lack of the MC1R gene being able to change one type of melanin into another. So when one copy of this gene does not work, you end up with freckles, and if the other copy also does not work, you end up with red hair too. So while the sun may affect how your freckles appear on your skin, the whole reason they came to exist in the first place is all thanks to your parents. Pretty neat! 

Family Pedigree and the Freckle Allele.

More on Genes and Freckles

All my life, it's been really hard for me to tan. After being at practice outside all day, or hanging out at the beach, I seem to get a little bit of a tan, but nothing crazy compared to some of my friends, who seem to tan so easily. At first I thought maybe it was because I was wearing too much sunscreen, (it's not, don't ever forget to wear sunscreen--there is no such thing as too much) but really it's just because of my genetics. I clearly inherited the dominant allele for freckles on my MC1R genes from my parents, since I have freckles all over my skin. Again, the MC1R gene encodes for a protein that produces melanin. This protein is found on the outside of melanocytes, which are the cells that are also responsible for producing melanin in our skin. When the MC1R protein detects UV rays, it signals to the melanocytes to produce melanin to protect our skin from being damaged. There are different types of melanin that can be produced in our skin- eumelanin and pheomelanin. There are two different types of eumelanin, which is black and brown. This kind of melanin is responsible for dark colors in the skin, hair, and eyes, and when there is little amounts of either eumelanin present, it results in things like blonde hair. Pheomelanin is the type of melanin that gives pigment to our lips, nipples, and other areas of our body that look pinkish. The MC1R protein changes pheomelanin to eumelanin, but the MC1R protein in people who have freckles actually doesn't change the pheomelanin into eumelanin that well, since the melanocytes are more clustered together and have more pheomelanin than usual. Since pheomelanin gives us that pinkish color on parts of our skin, the pigment of pheomelanin is red, which is why freckles have a light orangish color most of the time. 

Location of MC1R Gene on a Chromosome.

So, next time you think you aren't getting a good tan as a person with freckles, but you notice your freckles getting darker, what's really happening is that you are tanning, just in tiny little spots on your skin, which are your freckles. Pretty cool!

Let's Talk About X, Baby!

Have you ever heard the phrase "less is more?"  That quote applies to genetics, too!  Every female is born with two copies of the X chromosome, while males are born with one copy of the X chromosome and one copy of the Y chromosome. While this difference accounts for the designation of an individual's assigned sex, it also creates a large genetic problem called aneuploidy.  A female individual now has two copies of the same chromosome, which means she has too many genes.  Extra chromosomes can cause birth defects, like Down Syndrome which occurs after an extra copy of the 21st chromosome is made.

Karyotype Displaying Extra 21st Chromosome

So, how does one deal with this issue? The answer is X-inactivation, in which one copy of the X chromosome is condensed into a Barr body that becomes inactive because genes are not transcribed from it.  This occurs in autosomal cells during early embryonic development. This process is known as lyonization, named after Mary Lyon, the British scientist who discovered it.

Picture of Mary Lyon

To me, the most interesting part of this process is that it's completely random! It's impossible to know which chromosome will be deactivated, and in all female individuals, the same chromosome isn't deactivated everywhere.  The only exception to this is in kangaroos where the paternal X chromosome is activated over the maternal X chromosome.

A Kangaroo

This random activation and inactivation of X chromosomes means that all over a female individual's body, different genes are being expressed. This is called mosaicism, where two or more cell populations that have different genotypes are expressed in a single individual.  The best example of mosaicism caused by X-inactivation is found in a calico cat.  All calico cats are female because of X-inactivation.  For a male cat to be calico, they would have to have an "X"tra somatic cell.

A Calico Cat Displaying Mosaicism

This cat had parents that were likely orange and black.  On one X chromosome, there was a gene coding for black fur and on the other chromes there was a gene coding for orange fur.  Since X inactivation is random, the cat has multiple patches of black and orange fur across her body.  And if you were wondering, yes, female women are also mosaics!  Although mosaicism doesn't come through as obviously in female humans, it shows up in more subtle ways like a lack of sweat glands in certain parts of a woman's body.

In conclusion, ladies don't let anyone tell you otherwise; you are literally a mosaic and a work of art.

The Relationship Between Epigenetics and Oppression

Throughout the history of America, African Americans have faced extreme oppression and racism. Even today, African Americans are still suffering politically, socially, economically… and genetically. The systemic inequality found in this country has had an impact on more than just social status - it has influenced human biology at the cellular level, causing the oppressed to be more vulnerable to disease.

By studying epigenetics, the science of how external factors affect our gene expression and function, scientists have found that there are certain aspects of African American biology that have been negatively altered due to years of suffering under slavery and Jim Crow laws. The cells of people who have experienced a lot of physical or emotional abuse react strongly to stress, especially during development times in the womb, which can make the child more susceptible to disease later in life. The mistreatment that African Americans endure can alter the expression of certain cells that control important bodily functions, and that can also lead to more negative health consequences. It has been found that African Americans have a much higher level of cortisol, the body’s “fight or flight” hormone, than is normal for a human. This can reshape the behavior of cells that regulate blood pressure, kidney function, and cardiac function.
While this information may seem contrary to all that Darwin has taught us about evolution, it does not actually refute his findings. Rather, it adds to it, providing us with a deeper and more complex understanding of the ways in which evolution works and affects our lives.

After centuries of mistreatment towards African Americans, epigenetics is revealing that they are not only more prone to worse social and economic situations - they are also more prone to diseases. This issue is especially important in the debate over reparations, and I think that more research should be conducted into the role of epigenetics in the lives of descendants of those who suffered under slavery and Jim Crow laws.