Hi there! I’m Kate from MinuteEarth, and today we’re diving into the fascinating world of dogs and cats. Have you ever noticed how different dogs can look from one another? My dog, Watson, looks one way, but there are dogs out there that look completely different. It’s almost like they’re not even the same species! Cats, on the other hand, tend to look and act more alike. So, why are dogs so diverse compared to cats? Let’s explore this mystery together.
Even though dogs look incredibly different on the outside, their DNA tells a different story. Surprisingly, dogs are quite similar to each other genetically. In fact, the DNA differences between dogs are about the same as the differences between their human owners. Cats, however, have more genetic variation than dogs.
So, why do dogs look so different if their DNA is so similar? It all comes down to how we’ve bred them over the years. Imagine you have a bunch of colored dots. If you split them into groups, each group could have all the colors, or each group could be just one color. This is what we’ve done with dogs through selective breeding. We’ve created distinct groups, or “breeds,” where dogs within a breed are quite similar, but very different from dogs in other breeds. This is why dachshunds have short legs and greyhounds have long legs, even though their DNA isn’t that different.
Cats, on the other hand, haven’t been bred as selectively as dogs. This means that even though cats have more genetic diversity overall, the differences within each breed aren’t as pronounced. So, cats within a breed can still be quite different from each other, and cats from different breeds can be somewhat similar.
When it comes to humans, people from different populations don’t have much more in common genetically than they do with people from other populations. Interestingly, just a few spots in the dog genome have a big impact on how they look. For example, only 14 genes account for most of the size differences in dogs, while hundreds of genes affect human height and body size. This makes it easier to breed dogs with huge size differences.
Dogs aren’t the only example of selective breeding. We’ve also bred chickens to have a 15-fold size difference and transformed a plant called Brassica oleracea into many different forms. So, while cats might seem similar now, with more selective breeding, we could potentially create cats as diverse as dogs. But before we start breeding giant cats, we should think about any unintended consequences that might arise.
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Imagine you are a dog breeder. Design a new dog breed by combining traits from different existing breeds. Draw a picture of your new breed and write a short description of its characteristics and what makes it unique. Share your creation with the class and explain why you chose those specific traits.
Participate in a role-play activity where you and your classmates act as different breeds of dogs and cats. Each student will receive a card with specific traits. Walk around the classroom and find others with similar or different traits. Discuss how selective breeding might have influenced your traits and how this relates to genetic variation.
Work in groups to solve a puzzle that illustrates the concept of genetic similarity and diversity. Use colored beads or paper strips to represent DNA sequences. Arrange them to show how small genetic differences can lead to significant physical diversity in dogs compared to cats. Present your completed puzzle to the class.
Engage in a classroom debate about the pros and cons of selective breeding in animals. Divide into two groups, with one group supporting selective breeding and the other opposing it. Use examples from the article and additional research to support your arguments. Conclude with a class discussion on the ethical implications of selective breeding.
Choose another species that has been selectively bred, such as chickens or plants like Brassica oleracea. Conduct research to learn about the history and impact of selective breeding on this species. Create a presentation or poster to share your findings with the class, highlighting similarities and differences with dog and cat breeding.
Sure! Here’s a sanitized version of the transcript:
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Hi, this is Kate from MinuteEarth. My dog Watson looks like this. But there are also dogs that look very different from him. They’re so diverse that they barely seem like the same species. While there are some unique variations in the feline world, cats generally look and act much more similarly to each other than dogs do. So yes, dogs are much more diverse than cats… except they also aren’t. Because beneath all those superficial differences—what scientists refer to as “phenotypic diversity”—domestic dogs are surprisingly similar in terms of DNA. On average, only a tiny fraction of dogs’ DNA differs from each other, which is about as much as the variation among their owners, and several times less than the genetic differences typically found among cats.
So why do dogs appear and behave so distinctly compared to humans or cats? It has to do with how genetic differences are distributed within a species. Instead of genetic differences, let’s visualize this with colored dots. Imagine you have a collection of dots in equal numbers of four different colors. Now, divide those dots into four groups. Within each group, you could have all the colors represented, meaning each smaller group would include all the diversity that exists among the dots as a whole. Alternatively, each group could consist of dots of just one color, resulting in individuals within each group being quite similar to each other, but very different from individuals in the other groups. This is similar to what we’ve done with dogs.
Over centuries of selective breeding, we’ve partitioned different genes and variants of genes into distinct groups of dogs. As a result, dogs in different groups—known as “breeds”—are genetically quite similar to each other and very different from dogs of other breeds. That’s how, even without a lot of genetic variation, we’ve ended up with dogs that have such distinct characteristics, like stubby legs in dachshunds versus long legs in greyhounds.
Compared to dogs, cats have more overall genetic diversity, but since we haven’t been breeding cats as long or as meticulously, their categories are less well-defined. Each breed still contains a lot of the genetic diversity that exists in the species as a whole, so cats within a breed aren’t all that genetically similar, and cats of different breeds are somewhat similar.
As for humans, people within any one “population” don’t have much more in common genetically than they do with people from other populations. Additionally, for reasons we don’t fully understand, a few spots in the dog genome have significant effects on a dog’s appearance. Variation in just 14 genes accounts for almost all the variation in dogs’ size, compared to the several hundred genes that contribute to humans’ height and body mass index. This makes it relatively straightforward to create dogs with a forty-fold size difference.
However, dogs aren’t the only examples of this. We’ve also bred chickens with a 15-fold size difference and transformed a humble plant called Brassica oleracea into a diverse array of forms. So even though cats today seem quite similar, with another hundred years of careful selection, we could likely breed cats that vary as much as dogs do. But first, we might want to consider whether breeding giant cats could lead to unintended consequences.
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Dogs – Domesticated mammals that are often used in genetic studies to understand inheritance patterns. – Example sentence: Scientists study the genetics of dogs to learn more about inherited traits and diseases.
Cats – Small domesticated carnivorous mammals that are often used in genetic research due to their varied coat patterns. – Example sentence: The genetic diversity in cats helps researchers understand how different traits are passed down through generations.
DNA – The molecule that carries the genetic instructions for life and is found in the cells of all living organisms. – Example sentence: DNA contains the information needed to build and maintain an organism, including humans, dogs, and cats.
Genetics – The study of heredity and the variation of inherited characteristics. – Example sentence: Genetics helps us understand how traits are passed from parents to offspring in all species.
Breeding – The process of mating organisms to produce offspring with specific traits. – Example sentence: Selective breeding in dogs has led to a wide variety of breeds with different characteristics.
Diversity – The range of different inherited traits within a population or species. – Example sentence: Genetic diversity is important for the survival and adaptability of species like cats and dogs.
Species – A group of organisms that can interbreed and produce fertile offspring. – Example sentence: Dogs and cats are different species, each with unique genetic makeups.
Variation – The differences in physical traits among individuals of the same species. – Example sentence: Genetic variation in a species can lead to differences in appearance, such as fur color in cats.
Traits – Characteristics or features of an organism that are determined by genes. – Example sentence: Traits like eye color and fur length in dogs are inherited from their parents.
Humans – Homo sapiens, the species of bipedal primates to which modern humans belong, known for their complex genetic makeup. – Example sentence: Humans share a large percentage of their DNA with other species, including dogs and cats.
