HW: Corn, Dogs, and Genes

Read the following article and answer the questions. If needed, use headphones and listen to the text using Text to Speech.  

Remember to RAUR:

Read (or listen to) the question

Understand the question

Answer the question

Review the answer to the question

1. Have you ever heard that all dogs are related to wolves? For some dogs, such as huskies, German shepherds, and Akitas, the resemblance to wolves is quite striking. You can see how they may be related. But what about other dogs? Pugs look nothing like wolves. Neither do Chihuahuas, dachshunds, or toy poodles. Yet these dogs are also distant relatives of the wolf. So how did we get from wolves to toy poodles? The answer is artificial selection. Humans change specific characteristics of organisms by a process known as selective breeding.

2 How have humans been able to choose which traits of organisms are passed on to offspring? Selective breeding is a process in which humans choose the genetic traits they want in the offspring of a plant or an animal. These genetic traits are determined by the genes found in DNA that are passed from parent to offspring in each generation. Parent organisms with the desired genetic traits are chosen to breed with each other. This increases the chance that the offspring will also have the desired traits. Over several generations, selective breeding can produce changes in the genes of organisms that can result in a new breed or variety within a species. Humans have used selective breeding to develop a wide variety of breeds in some species, such as dogs, cattle, corn, and apples.

3. Grains are an example from very early in human history. People would selectively breed certain types of grains in order to grow more bountiful crops. They would choose plants with the traits that they desired. By choosing those traits, people were then able to change the gene pool of the plant to get populations that they wanted. Let us use corn as an example. The corn that we know today grows on very tall and sturdy green stalks. Each stalk has several large ears of corn. Each ear has outer layers of tough green leaves to protect the hundreds of beautiful yellow kernels found underneath. The corn that we know takes two hands to hold and eat. A person can have a fairly good meal with one ear of corn. But the corn of prehistoric times did not look at all like the corn that we use for food today. Prehistoric corn looked much more like modern day wheat. It grew on small stalks, and the kernels were not protected by thick green leaves. So how did it change from a wheat-like plant to what we know today? Selective breeding. Artificial Selection Natural Selection 1 Corn, Dogs, and Genes

4. The change began when people started the practice of agriculture, or growing their own crops. The theory goes that they began to notice that certain plants had different traits than other plants. Some plants had larger fruits. Some plants had stronger stalks. Some plants grew taller. So people began to use only the seeds from the plants that had the traits that they wanted. In other words, they chose the plants with the genes that they wanted. In the case of corn, people most likely only planted the seeds of those plants with the larger kernels. In other words, they selectively bred the plants that had the genes that they wanted, such as the gene for larger kernels. With each new generation of corn, only those plants with the largest kernels were replanted. Over generations, corn grew larger and larger kernels. Several thousand years later, selective breeding changed the gene pool of corn and created the corn that we know today.

5. Let us go back to the dog example. Dogs have been documented to have been a part of human culture for at least 7,000 years. Archeological evidence shows that early humans domesticated wolves perhaps as far back as 20,000 years ago. Early humans likely adopted orphaned wolves to keep for both protection and for help with hunting. A modern day experiment called the “farm fox experiment” explores how species of animals can become domesticated. Certain individual animals show less fear towards humans. These animals are bred to animals with this same trait. Their offspring also have less natural fear of humans. Over many generations, the fear of humans can actually be bred out and replaced with affection for humans. In this way, animals can be domesticated. Therefore, it is hypothesized a similar process occurred when early humans domesticated wolves into the dogs that live with us today.

6. The domesticated dog did not change much for many thousand years. But as civilization changed, so too did the need for different types of dogs. This led to the many different breeds of dogs that we see today. Dogs that were very good at hunting were only bred with other dogs that were very good at hunting. This led to a variety of hunting dogs, from bird dogs to big game dogs. As towns and cities grew, there was greater need to get rid of rodents. In these cases, small dogs that could fit in holes and under buildings were greatly desired. These dogs also had to be fierce in temperament. Therefore, dogs with these traits were selectively bred, leading to breeds such as the terriers. As society changed, those from wealthy families desired small and pretty dogs to play with. So dogs were selectively bred that were kind, had silky coats, and could be carried under the arm. This led to breeds such as the toy breeds.

7. The domestication of animals and selectively breeding crops have helped people. There are other ways that we have altered the genes of organisms to benefit society. Advances in modern science have allowed genetic outcomes to be changed through artificial selection in other ways. In gene therapy, DNA itself is used to help fight specific types of diseases. In the most basic sense, properly working genes are used to replace mutated genes. Somatic gene therapy works to treat the non-reproductive cells of people. Therefore it can only be used for individuals with a disease. Clinical trials look promising. But gene therapy has not yet been shown to completely correct genetic disorders. Who knows where this next level of artificial selection could take us with future studies. One day we may be able to select gene treatments that cure any type of disease!