A lot of people are wearing mismatched socks today, and it's a fashion choice with a purpose. It's meant to call attention to World Down Syndrome Day, which celebrates the lives of people with Down syndrome, raises awareness about the condition and highlights the role that people with Down syndrome play in their communities. In honor of the day, people around the world are sharing photos and videos of their mismatched socks using the hashtag #RockYourSocks.

The day is celebrated March 21 because the date symbolizes the 3 copies of the 21st chromosome, the genetic anomaly which leads to Down syndrome. Typically, the nucleus of each cell contains 23 pairs of chromosomes, but an extra copy occurs in people with Down syndrome, altering the course of development.

According to the Centers for Disease Control and Prevention, approximately one in every 700 babies in the United States is born with Down syndrome, making Down syndrome the most common chromosomal condition.

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The idea of Rock your Socks was born from the chromosomes themselves, which are shaped a bit like socks. To celebrate and raise awareness for Down syndrome, which is also known as Trisomy 21, people are wearing their brightest socks and sharing the pictures on social media.

Teen climate activist Greta Thunburg — who has Asperger's syndrome and was recently nominated for the Nobel Peace Prize — rocked her socks on Instagram, along with thousands of others.

These are chromosomes. The ↘️ is 21 (note 3 copies) This is Trisomy 21 aka Down syndrome. They look like socks, right? 🧦 Today is #WorldDownSyndromeDay! A great day to ‘Rock Your Socks’ - celebrate and raise awareness by wearing your brightest mismatched socks! 💙💛 #pinksocks pic.twitter.com/RjIaKNU8UG — Larry Gioia 🔠✨ (@LGin412) March 21, 2019

To mark #WorldDownSyndromeDay Matthew and I are wearing odd socks to show that one different chromosome doesn't make a difference. pic.twitter.com/T9aBBiNKCZ — John Swinney (@JohnSwinney) March 21, 2019

In 2017, CBS News' Elaine Quijano traveled to Iceland to explore how the widespread use of genetic testing there has resulted in a steep decline in the number of babies being born with Down syndrome. Some are troubled by a society that can "pick and choose" which children get born. You can watch the full story in the video below: