Science project

Species vs. Breed

The purpose of this experiment is to breed a pair of mice, a pair of rats and a mouse and a rat in order to learn about the difference between a species and a breed.

  • What is a species?
  • What is a breed?
  • How were different dog breeds created?
  • Is it possible for two animals of different species to procreate?
  • If it is possible, how do scientists know that these two animals were really in different species?

Even scientists sometimes have trouble telling the difference between a species and a breed. Every year, animals are reclassified when we learn more about their genetic compatibility. For years, a species has been defined as a population that is capable of interbreeding, but recent developments in our understanding of genetics has altered our understanding slightly. Now, a species is a group of animals that not only can, but does interbreed. Isolated breeding populations, if kept from the larger group, do eventually evolve into their own species. Usually, species of animals look similar from member to member. The main exception is the domestic dog, which comes in many different shapes and sizes. Though a Chihuahua and a Great Dane may look very different, they can be interbred, and are thus different breeds of the same species of animal. Learning about which types of animals are distinct breeding populations and which types of animals are actually breeds of the same species is important so that scientists can further understand the evolution and the differentiation of animal species. 

  • 3 cages
  • 2 female rats
  • 1 female mouse
  • 2 male mice
  • rodent food
  • bedding
  • an observation log

You can purchase the needed supplies at a pet store. It may also be possible to borrow cages and even mice and rats from friends or from your school’s science lab. Your local pet store will usually take baby mice and rats once they are old enough to be separated from their parents, but you should check with them first.

  1. Set up the cages with bedding, food, water and toys for your mice and rats to play with.
  2. Place a male and female mouse in one cage.
  3. Place a male and female rat in another cage.
  4. Place a male mouse and a female rat in the third cage. While you could use animals of the opposite genders, a female rat is more likely to be docile around a male mouse and thus the two animals are more likely to get along.
  5. Take observation notes on each of the cages daily. Use an observation log such as the one below.
  6. After about a month, the females will likely give birth. You will be able to see the pregnancies progress. If there is no sign of pregnancy after a month, check to make sure the animals are the correct genders. You can then give them another month.
  7. Take notes on the pregnancies and on the offspring that are born in each cage.
  8. After a few litters are born, you will be able to verify through your experiment whether mice and rats are different breeds of the same species or whether they are two different species.








The two mice played together on the wheel for five minutes. The male went to the food dish and ate some seeds. After a couple minutes, the female joined him and the two ate together for 4 minutes. Then the male took a bath while the female slept in the nest corner.






Terms/Concepts:  Species;  Breed; Genetics; Evolution; Hybrid; Viability; Selective Breeding



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