Understanding DNA
The Letters that Define Life
Like most siblings, 12-year-old Onna Okeke and her 11-year-old brother, Toby, have a lot in common. For starters, they look alike, sharing many similar facial features. They both love the cold, snowy winters of Canada, where they live. They also are both very athletic and enjoy playing sports.
But Onna and Toby have plenty of differences too. People say Onna looks more like their dad, while Toby looks more like their mom. Onna is a competitive swimmer; Toby, on the other hand, plays competitive ice hockey. So where do the similarities and differences come from? What is it that makes each person so unique – even when they are siblings? Let's get to the bottom of this together.
What Makes Us Who We Are?
Onna and Toby also share a love of science and computer coding, but they have different motivations. Toby loves playing video games and is learning to code so he can program his own game someday. Onna isn’t really into video games, but is learning a different coding language because she would like to program a robot!
It was while the siblings were telling their parents about their different coding interests one evening over dinner that the question struck Onna: “How can siblings who share the same parents be so different?” she asked. “Why do some siblings look so similar and others don’t resemble each other much at all? And why don’t Toby and I have exactly the same skills and interests?”
Do other siblings ever wonder the same thing? Let’s find out.
DNA and the Genetic Code
“Humans have been asking ‘what makes us who we are’ for thousands of years,” said the siblings’ dad with a smile. “Scientists only began to formulate a good guess about 160 years ago. Lucky for us, incredible research over the past 20 years has finally made it possible to really explain.”
“So…what is the answer?” asked Toby. “The short answer is just three little letters: D-N-A,” said their mom. “Just as computer programmers write code when they develop a game or any kind of application, and the code gives the computer instructions about what to do, DNA is part of a special instruction code that tells our body’s cells what to do.”
For a long time, scientists knew that DNA existed and that it was a code, but they had no idea what the code meant. It was only about 30 years ago that scientists from around the world collaborated on the Human Genome Project, working to sequence the entire human genome for the first time.
“Good comparison!” said their dad. “You know how binary computer code is made up of only two digits, 0 and 1, that repeat over and over – and it’s the order they’re written in that tells the computer what to do? Our body’s instruction code is written in 4 different DNA bases, designated by the letters A, T, G, and C, which also repeat over and over. Sections of DNA bases called genes contain the information our cells need to make different proteins, which are the building blocks for everything in our bodies. But again, it’s the order and repetition of the DNA base letters that determine how those proteins are built and are largely responsible for who we are – what we look like on the outside and how we think and function on the inside. Just like with video games or robots, variations in the code result in slightly different programs.”
Where Do We Get Our Genes?
“Wow!” said Onna. “I’ve heard of DNA and genes before, but never really understood what “genetic code” meant. Now I think I get it!”
“Me too!” smiled Toby. “Our genetic code is the set of instructions that makes us who we are.”
“You do get it,” beamed their mom. “Our environment also plays a role in shaping who we are, but many of our characteristics, or traits, are determined by our genes. The physical expression of a genetic trait is called a phenotype. For example, I have a brown eye color phenotype and so do you. And the study of how different traits, like brown eyes, are passed down from parents to children is called genetics.”
“Wait – so Onna and I get our traits from you guys?” asked Toby.
When we describe the look of a living thing, we are describing its phenotype. A phenotype is the set of observable characteristics of an organism – all the physical traits that can be seen or measured in a laboratory (such as blood type). But what determines an organism's phenotype? It's mostly our genes! Not the kind we wear (jeans), but the tiny sections of DNA that are found in our body’s cells. Try our fun Genetics Challenge to learn more!
“You’re a pretty smart kid. You must have inherited that trait from your mother,” said their dad with a wink and a smile. Then he continued: “Our genes are grouped into separate packages called chromosomes. Humans have 23 matching pairs of chromosomes, or 46 total. A child inherits one chromosome from each pair from each of its biological parents. So Toby, you might have gotten one chromosome in one pair from me, and Onna might have gotten the other chromosome from that pair. Or you both might have inherited the same chromosome from me, but different ones in the pair from mom. There are many, many possible combinations – which helps explain why sometimes siblings are similar and sometimes they are very different. It also explains how kids can look very different from their parents.”
“But what determines which chromosomes each child inherits?” asked Onna.
“That is quite random – almost like nature flipping a coin,” said their mom. “Actually, while we’ve been talking I’ve done a little research on my phone and found a fun-looking activity that looks like it will help you get a much better understanding of how genetics works. Want to give it a try?” “Sure!” exclaimed the ever-curious siblings.
And why should you be left out of the fun? You can try it too!
What does DNA look like?
“That was really fun. I like our little Mixie creations,” smiled Onna, who loves to create things.
“Yeah…and it was super interesting to learn how kids can inherit physical traits that are hidden in both of their parents!” added Toby. “I like things that are mysterious but can also be explained by science!”
“Speaking of hidden, how do scientists even know what DNA looks like?” asked Onna. “I’ve certainly never seen my DNA.”
“No, of course not,” said their dad. “DNA is much too tiny to see with the naked eye. It requires a microscope. But thanks to the work of scientists, we know that a DNA molecule looks a lot like a ladder twisted into a spiral. Each rung of the ladder is made of two bases linked together in the middle - A , T, G, and C, remember? The length of a DNA molecule is often measured by how many rungs, or base pairs, is in the ladder.”
“Does everything that’s alive have DNA – and if so, does it look the same as human DNA?” asked Toby.
Humans have 23 pairs of chromosomes
...nearly as many as pineapples, which have 25 pairs, but far fewer than dogs, which have 39 pairs!
“A two-part question earns two scoops of whipped cream,” smiled mom, who was now preparing some delicious strawberry shortcake for dessert. “First, yes – every living organism has DNA: animals, plants, bacteria. Some viruses even have DNA, even though they’re not technically alive. Second, yes, somewhat – the cells of all animals and plants contain DNA in the same shape – the famous ‘double helix’ that looks like a twisted ladder. But each species has a specific number of chromosomes, so not all have 23 pairs like humans do.”
Dad picked up a big juicy strawberry – but instead of taking a bite, he held it up in the air. “For example, strawberries have 7 chromosome sets, and 8 chromosomes in each set instead of pairs. Do you know what that means?”
Toby and Onna looked at each other for clues, then shook their heads no.
“It means that since they have 8 copies of DNA, it’s easier to see the large groups of strawberry DNA threads with the naked eye. Anyone up for a little strawberry DNA extraction experiment?”
“Let’s do it!” exclaimed Toby. Then he added with a grin, “Right after dessert.”
How Can DNA Research Help Solve Health Problems?
The next day after school and swim practice, Onna still had DNA on her mind. Since she loved to cook, she volunteered to help prepare dinner so she could talk it over with Mom a bit more. On the menu: savory meat pies, a family recipe her mom had brought with her when she moved from Nigeria to Canada many years ago.
“Mom, why do you think it is important for scientists to study DNA?” Onna asked, as she rolled out the pastry dough. “All the stuff we learned yesterday about genetic code and chromosomes and dominant or recessive traits…that’s really fascinating. But what do they do with that information?”
“Excellent question,” said her mom, as she stirred the aromatic sautéing beef and chopped veggies. “But first, let me ask you a question. We have this delicious recipe for meat pies, with a special combination of ingredients and spices that we think make them taste perfect, as they have been prepared for generations. What if I wrote this recipe on a new card to pass down to you, but when I wrote it, I accidentally left off an ingredient? Or wrote a measurement down wrong?”
“If I followed that recipe, the pies wouldn’t taste right,” answered Onna.
“Right,” said Mom. “And I would have to look at the recipe, identify the mistake, and then fix it. Well, some genetic diseases are caused by a simple mistake in the recipe, or a glitch in the genetic code. Now scientists are able to point to specific places in the genome and say, ‘That’s where the mistake is.’ And – even better – instead of just treating the symptoms of diseases that were once impossible to fix, they have been able to cure some diseases by either repairing or replacing the broken gene with a healthy copy. That’s called gene therapy.”
“Wow!!” exclaimed Onna. “That’s amazing!”
“It really is!” agreed Mom. “And it’s so exciting to read about the other ways that knowledge of the genetic code will continue to make improved medical treatments, vaccines, and even personalized medicine possible. But that’s not all! Over the past 20 years, scientists also have been sequencing the genomes for many plants, including the food crops we eat – like these potatoes and carrots,” she gestured, as she scooped the pie filling onto the dough. “And that will enable them to find solutions to problems with food production around the world.”
“Can you tell us more about that?” asked Toby, who had followed his nose into the kitchen.
“Actually, you two have had such good questions that I think it would be even better to let you talk to a real DNA expert,” said Mom. “I’m going to arrange a call with a scientist from my company.”
The next day, Onna and Toby were on a video chat with Dr. Monika Lessl, who leads Corporate Research and Development and Social Innovation at Bayer. Play the video to hear what she had to say!
How Can DNA Research Improve Food Production?
“That was crazy. I’ve never thought of plant seeds like that before!” Onna exclaimed after their conversation with Dr. Lessl. “Me neither!” said Toby, as he shook his head in surprise.
“Like what?” asked their dad, who had just walked into the room.
“Like they are genetic recipes that are always being tweaked. Did you know that, Dad?” asked Toby. “I have always thought that fruits and vegetables had been the same way since…well, forever.”
“You know, I used to think the same thing,” their dad admitted. “It has only been pretty recently that I learned that humans have been selectively breeding crops for more than 10,000 years, so almost none of the fruits or vegetables we think of as ‘natural’ today actually began that way. In fact, check out this video that shows how much some of our favorites have evolved from where they originally started.”
“So how exactly does plant breeding work?” asked Onna.
“Well, the basic genetic principle works the same way it does with people,” said Dad. “Two parent plants produce offspring that inherit traits from each parent. In traditional plant breeding, people would choose parent plants with traits they wanted the offspring to inherit, but just like the coin toss in our activity, they couldn’t control which genes were actually passed on. Today, newer methods of plant breeding are much more precise and enable scientists to simply add a specific beneficial trait or turn off a problem trait without changing the rest of the plant’s genome.”
“You’ve read about the Irish Potato Famine of the 1800s in your history books,” added Mom. “One million people died when a disease destroyed the potato crop – their primary food source – for several years in a row. Imagine if they could have bred a gene for disease resistance into the crop. In the future, famines that would have been caused by crop diseases or pests or drought will be averted thanks to scientists knowing how to breed plants that will be able to withstand those challenges.”
“That’s a pretty awesome way of using science to help people,” Onna smiled.
“It has been really cool to learn so much about DNA,” said Toby. “Now I know it’s probably not your fault that you don’t like video games,” he teased his sister. “You’ve just received the ‘wrong code’ from mom and dad.”
“Ha ,” Onna retorted with a smile. “And maybe that explains your bad jokes too.”
“Alright, now we’re back to the sibling rivalry I’m used to,” laughed their Mom. “You know what? Whether you want to call it a code or a recipe or the text in a book, I think both of your DNA is just right. And I’m glad you’re not exactly the same, because you have different strengths to offer the world. If you keep studying science, I can’t wait to see what kinds of problems you each might try to solve someday.”
“Now that’s something we can all agree on,” said Onna, giving her brother a high-five. Then they headed back to their rooms to think about video games and robots and making the world a better place.
