| Unit II Objectives |
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In Unit I, we looked at how organisms are made up of cells. In those cells are combinations of instructions or recipes guiding their work. As succeeding generations of organisms are produced, new combinations are formed. These are genetic combinations formed naturally. In this unit, we will examine how this genetic change comes about.
Genetic change occurs naturally through a process known as natural selection and mutations. Alternatively, different combinations can also be achieved through human intervention. Did you know that broccoli, cauliflower, cabbage, kale, and Brussels sprouts all came from one species of a wild mustard? This amazing variety would probably not have occurred if not for human intervention.
These interventions are what biotechnology is about. For our purpose, let us define biotechnology as:
the use of biological organisms, systems, or processes to make or modify products.
Biotechnology can be characterized as old and new. What is being referred to as Old Biotechnology does not imply that it is out of date. It simply refers to the methodsof manipulation that have existed for centuries. On the other hand, New Biotechnology refers to the techniques which developed with the discovery of DNA and to applications in new areas that have not been understood previously.
How do we "manipulate" these changes and processes? What are the limitations of our efforts? Why do we do so? What are the benefits and the risks of our interventions? We will consider these questions in this unit and the next.
How can we tell that genetic changes are natural? Let us take a look at family trees.It is easy to see how a line of similarity runs through our families. At the same time, there are also clear differences.
Changes in genetic information are natural and occur at random. In sexual reproduction, virtually millions of genetic combinations are possible. Thus, it is reasonable that within one family, there can be much genetic variation in terms of physical traits and even preference traits.
Through successive generations, considerable genetic variation can occur naturally. Over time, new varieties or species evolve when there are changes in the genetic code. Nature allows for this through two processes: natural selection and mutation.
Natural selection is what happens when species which have the traits that help them adapt to the environment survive and reproduce. Their genes get passed on to the next generation.
The "Tale of Two Moths," an activity in this unit, recounts how the light gray, spotted variety used to be in abundance in the English countryside. They were camouflaged when resting against a backdrop of light-colored lichen. In contrast, the dark-winged variety made easy targets for predators. However, with the Industrial Revolution at the turn of the 19th century, factories were built on a large scale, producing unprecedented levels of pollution which killed the lichen on the rocks. As a result, the dark-winged moths were better able to blend in with their surroundings, while their spotted cousins stood out and were driven close to extinction.
This is in fact a classic tale of natural selection among the English Peppered Moth or the Biston betularia. Over a long period of time, if the pollution of the Industrial Revolution had not been checked, there might be enough changes in the genetic information that could lead to the evolution of new species of the moth.
Evolutionary changes may occur gradually over millions of years: new generations differ in small details from the previous ones. Evolution may also take giant leaps with dramatic changes occurring in just several hundred or thousand years.
In either case, clearly, we would not be able to observe or gain much genetic variation in our lifetime.
However, we can and do observe genetic variation in nature. This is possible because genes sometimes mutate. Recall from Unit I that every organism has its own unique recipe book of genes that ultimately determines what traits an individual organism has.
Cells divide to make more cells. This is how organisms grow. In this process, DNA is copied. Mutations are the rare mistakes made during copying. Suppose we tried to copy the recipe for cupcakes but by mistake, noted 1 tbsp of salt instead of 1tsp, we would get a different result.
Usually mutations cause little harm. However, sometimes, mutations can cause disease, e.g. cancer. At other times, new traits result that can actually benefit the organism. For instance, some insects are resistant to pesticides because of mutations in their genes. So, they survive and breed a new generation of insects with this resistance.
Or think of why we need to finish a course of antibiotics when we have a throat infection, usually 7 days. If we stopped the treatment after 4-5 days, infection may recur. This time, there is a chance that new bacteria which has mutated may be resistant to the antibiotics, rendering it ineffective.
Mutations happen by chance and at random points of the DNA chain. They can also result from radiation, exposure to certain chemicals like dioxin, tobacco, and UV radiation. Mutations are an important natural source of genetic variation. They can contribute to an increase in the chances of survival for a species.
Selective breeding involves cross-breeding closely-related species, usually through the normal reproductive means. Just think of the champion horses specially bred for their speed or even our pet dogs.
With plants, it is possible to cross-breed using cuttings and other asexual means. This ancient practice uses the whole or some substantial part of an individual organism.
This practice may also be referred to as artificial selection, as opposed to natural selection. People select the individual animal or plant that has a certain trait useful to human beings, for example, strength or quick growth rate. These individuals form the breeding stock and new generations with these traits can be bred.
We should note that selective breeding is in fact a form of genetic manipulation because we are selecting organisms that have those genes we want, giving them a greater chance of being reproduced. In this way, we modify the original species.
| Selective Breeding of Dogs | |||
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| Type of Dog | History of Origins | Traditional Status | Current Status in the U.S. |
| Poodle: standard miniature toy | Germany. Popular in France since the 19th century. | water retriever | water retriever, watchdog, pet |
| Bulldog | Britain | bullbaiting | British mascot, pet |
| Siberian Husky | Siberia. Imported into Alaska in 20th century. | sleddog, watchdog, pet | pet, sled dog racing |
| Akita | Japan. Imported into the U.S. in 1937 | guard dog, hunting, spiritual symbol | pet |
Suppose Farmer Brown owns a field of broccoli, which is part of the cabbage family. With a keen eye, Farmer Brown observes that some of the broccoli grew faster than others. The farmer also found other broccoli that survived a disease called "soft rot." If only Farmer Brown could have broccoli that both grows fast and is disease-resistant. Farmer Brown began to dream ....
And Farmer Brown can! The farmer can collect the seeds from the top 10% fastest growing broccoli and the healthiest plants. These will form the parent plants. If grown side by side the plants can cross-pollinate and form hybrids. Bees are very helpful for this task.
When the new plants mature, Farmer Brown will collect the seeds which display both the desired traits -- the hybrids -- and repeat the whole breeding process. After many generations of breeding, Farmer Brown is very likely to get the dream crop of broccoli.
Selective breeding is also applied to animals such as sheep, horses, and cattle. The process is much like what Farmer Brown did to achieve his dream crop.In plants, by very specific and careful cross breeding, it is possible to create new species that look very different from the original. Thus, from the wild mustard,we can have kale, red cabbage, broccoli and cauliflower.
Similarly, the American pioneers we met in Unit I in the activity, "Abundance of Apples," used the same process to cultivate larger, redder, and juicier apples.
Selective breeding might sound easy but there are some practical limitations.
| Materials |
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| Purpose of Activity |
| Use this activity to discuss natural genetic changes over time. |
Have the students take home the handout. They can complete the handout with their families.
Students choose 4 colored markers. With:
Explain that over time, there are natural genetic changes. Changes can occur within one generation or more gradually over many generations.
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| Purpose of Activity |
| Use this activity to discuss how natural selection works. |
At least three days before this session, select some type(s) of fruit: strawberries,grapes, cherries, berries, bananas, etc.
Separate the fruit into four groups.
Let sit for at least 3 days.
Place each group of fruit into a different bowl. Place the bowls on a table. Have the students examine the four bowls of fruit.
Create a scorecard for the fruits (on next page). Compile the scores and rank the bowls of fruit. After scoring, let the students choose which of the bowls they would prefer to eat.
Let them eat the fruit while discussing the following questions.
Explain that nature "selects" the better or "fittest" organisms in a species to go on and reproduce. When a fruit is attractive, the chances of it being eaten is higher than less attractive fruits. In the wild, the chances of the seeds (from the attractive fruit) bearing a new plant and surviving is also increased, when animals leave the seeds in places where they can germinate.
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| Purpose of Activity |
| Use this activity to illustrate natural selection in action. |
Before the activity, prepare 2 branches or logs. Leave one log as is. Glue bits of newspaper on the other log.
Tell the students that they are going to understand one reason why genetic change occurs naturally. Hold the "moths" that the students made in the previous unit in front of the class. Tell them that the different colors will affect the chances of their survival.
Preface the story with the following questions:
Smokestacks at factories can be rather black because of the soot deposited from burning fossil fuels. The first factories were built in England nearly 200 years ago at the time of the Industrial Revolution. Share with students the following tale:
Now in those days when there were yet no factories, and folks still moved around by a horse and cart, all that could be heard on a hot summer afternoon was an occasional duck calling and the snore of a farmer leaning against a great oak in the shade. Just outside London, there lived two types of moths. One of those moths had light gray wings speckled with dark spots (hold up the mixed colored moth). The other had wings all a dark gray (hold up the moth with the solid color).
The moths loved to dance in the light of the dawn, chasing each other, visiting every tree and rock.
They did not have a care in the world, until at mid-day, it got far too hot and the moths needed to take a nap.
"Nothing like a soft bed to rest on in this heat," said Pepper, one of the speckled kind, as it made itself comfortable on its favorite tree (show them the spotted moth resting on the log covered with bits of newspaper). The tree was covered with a lovely light-colored lichen (explain that lichens are moss-like growths made up of fungus and algae).
"I couldn't agree more," said Bold, its dark-winged cousin (let the other moth also rest on the newspaper-covered log).
Not too far away, a robin flew overhead. "I wonder what I should eat for lunch today," said the robin. It spied a worm crawling on a leaf and very quickly swallowed it. Suddenly, it spotted Bold on the tree. The two moths were oblivious to their danger. With one swoop, the dark gray moth was gone.
(Stop. Ask the children what they think had happened?)
Pepper woke up with a start and seeing what had happened, it quickly flew to a safe place where the robin could not reach it.
Not long after, people began to erect big buildings with tall towers that reached into the sky. The towers puffed out billows of smoke (Ask the children to guess whatthese towers are). Trees were cut down, and the land was cleared to build more tall towers for important people to do important work. Soon, a black cloud hung over the city and the surrounding countryside.
(Ask students what they think the black cloud is?)
This black cloud was a great nuisance. Laundry drying in the wind would be covered with fine black flecks; the beautiful bright days turned bleak and gloomy, as if a thunderstorm were about to break. But worse still, the black smoke was a poison to the soft lichen that covered the tree trunks which Pepper and his friends loved to rest on.
One day, after playing the whole morning, Pepper and its friends, some dark-winged and some speckled, visited their favorite tree at noon time as usual. But to their disappointment, they found the tree all hard and bare (show them the bare log). Gone was the soft lichen bed, leaving behind the dark tree trunk. Pepper and its friends flew to another tree but to no avail. All the trees were hard and stiff.By now they were so tired the moths did not care anymore. One by one, speckled and dark-winged, they dropped off to sleep. (show the moths resting on the bare log this time.)
Now, it is in the natural cycle of life that one organism is food for another. So, we are not surprised when another robin appeared as the moths were asleep. (Ask the children which moth the robin is likely to see more easily?)
From the top of the tree, the robin discovered the light gray moths and swiftly, it picked up one of the company, but all the dark-winged moths managed to escape.
Explain that pollution was an environmental factor that affected the natural selection process. Those moths that did not blend into their environment would be easily spotted and eaten. As a result, their genes would not be passed on to future generations. So over time, if pollution continued, the speckled moths might disappear because they would stand out against the dark tree trunks. If pollution were reduced, and the lichen were revived, chances are good that the speckled variety would return. This indeed happened in England.
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| Purpose of Activity |
| Use this activity to explore how genes and recipes create change in a species. |
Before carrying out this activity, mix one standard box cake mix--white or yellow preferably. Most box mixes make 1 1/2 to 2 dozen cupcakes. Bake 1/2 dozen cupcakes from batter--unaltered. Use these cupcakes for later comparison.
Have the students imagine that they are going to create "seeds" which they will "plant" from the batter.
Students may work individually or in teams. Give each student or team a cup and spoon. Into each cup, place enough batter for 1 cupcake.
Each team may choose 1 ingredient to add to their cupcake seed. Some teams may choose the same ingredient but different amounts can be used. For example, 1 cupcake seed may have 2 drops of lemon extract and another may have 1/4 teaspoon of extract. Each team should note the amount of the ingredient used.
Create an "accident." In one of the cupcake seeds, tell students you will pour 1 teaspoon of vanilla. Instead, pour 1 teaspoon of peppermint!
Place cupcake seeds in a muffin tin that has been lined with cupcake papers. Keep track of "seed" pattern. Record the placement of "seeds" (ingredients) on the paper.
Bake at the designated temperature for appropriate time. When finished, remove cupcakes and cool.
Have the teams compare their cupcakes. Explain that the batter is a cupcake "seed" and by baking it, they have planted a cupcake plant.
Compare the unaltered cupcakes to the cupcake plants. Have students taste an unaltered cupcake and the cupcake they "planted." Have the students taste each other's cupcake plants. Have them taste the cupcake you made with the peppermint instead of vanilla.
Explain that different cupcake plants were produced by introducing different ingredients. These ingredients are like the instructions in cells that tell the organism which traits to produce. Sometimes, changes in these traits can be seen, e.g. food coloring. At other times, changes in traits cannot be seen although the whole plant is affected. One cupcake plant tastes different from another.
Sometimes, changes in ingredients are made by mistake, like the one that you made. Mistakes happen in nature too. Explain that organisms grow by creating more cells. In the process, the instructions or genes are copied. When the instructions are copied incorrectly, a "mutation" is said to have occurred. Sometimes, the mutation does no harm. The cupcake plant is still good. At other times, disease can result.
However, we can also control how genes are combined, and intentionally produce different varieties of plants and animals. Recall how we can combine the different instructions in the "Abundance of Apples" activity to make a large, round, red and juicy, sweet apple. Or, think about the "Secrets of Ingot Theobroma Cacao." Sometimes, the same ingredients come together but with a totally different result. Selective breeding is an ancient practice of biotechnology.