CK-12 Life Science
Page 15
Thale cress (Figure below), a species of Arabidopsis (Arabidopsis thaliana), is a tiny weed that is often used for plant research because it is very easy to grow and its DNA has been extensively characterized. Scientists have identified a gene from this plant, At-DBF2, that gives the plant resistance to some environmental stresses. When this gene is inserted into tomato and tobacco cells, the cells were able to withstand environmental stresses like salt, drought, cold and heat far better than ordinary cells. If these preliminary results prove successful in larger trials, then At-DBF2 genes could help in engineering crops that can better withstand harsh environments. Researchers have also created transgenic rice plants that are resistant to a rice virus. In Africa, this virus destroys much of the rice crops and makes the surviving plants more susceptible to fungal infections.
Figure 6.18
Thale cress.
Lesson Summary
Using recombinant DNA technology, a foreign gene can be inserted into an organism’s DNA.
Cloning of mammals is still being perfected, but several cloned animals have been created by implanting the nucleus of a somatic cell into a cell in which the nucleus has been removed.
The Human Genome Project produced a genetic map of all the human chromosomes and determined the sequence of every base pair in our DNA.
Gene therapy involves treating an illness caused by a defective gene through the use of a vector to integrate a normal copy of the gene into the patient.
Review Questions
What is the enzyme used to cut DNA at specific points?
What is the term for all the genetic information of the human species?
What are the rings of accessory DNA in bacteria that are often used as a vector in genetic engineering?
What is the term for producing identical copies of an organism?
Can gene therapy cure a disease caused by a virus?
What is the vehicle used to introduce foreign DNA into an organism?
What is one disease that genetic therapy can help treat?
What supplies the cytoplasm of the clone’s cells during the cloning of an organism?
What is one application of recombinant DNA technology?
Is gene therapy for ADA deficiency a permanent fix?
Further Reading / Supplemental Links
http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml
http://history.nih.gov/exhibits/genetics/sect4.htm
http://learn.genetics.utah.edu/units/disorders/whataregd/ada/
http://www.lifesitenews.com/ldn/2007/nov/07112003.html
http://www.le.ac.uk/ge/genie/vgec/sc/genomics.html
http://en.wikipedia.org/wiki/Recombinant_DNA
http://www.hhmi.org/biointeractive/vlabs/transgenic_fly/index.html
http://www.na.fs.fed.us/fhp/ded/
Vocabulary
cloning
Creating an identical copy of an individual with the same genes.
DNA ligase
Enzyme that joins DNA fragments together.
gene therapy
Treatment that provides a new gene to replace a defective gene; potentially "cures" a genetic disease.
Human Genome Project
International effort to sequence all the base pairs in human DNA.
plasmid
An accessory circle of DNA in bacteria.
recombinant DNA
DNA formed by the combination of DNA from two different sources, such as placing a human gene into a bacterial plasmid.
somatic cell
A body cell; not a gamete.
transformation
The process by which bacteria pick up foreign DNA and incorporate it in their genome.
vector
A vehicle, such as a plasmid, used to transfer foreign DNA into an organism.
Points to Consider
Next we begin to discuss evolution, the change in species over time.
Fossils provide evidence of evolution, but what is a fossil?
If two animals are similar in structure, would you guess they are closely related? Why or why not?
Chapter 7: Evolution
Lesson 7.1: Evolution by Natural Selection
Lesson Objectives
Understand that inherited traits, such as the basic color of skin or a person’s bone structure, are passed on to future generations.
Understand that acquired traits, such as a tan or being good at soccer, are not passed on to future generations (they are not inherited).
Understand that evolution is change of an inherited trait in a population over many generations, such as the change of the color of moths living on an island over many generations.
Understand that natural selection means that organisms with traits that help them survive in their environment are more likely to survive than organisms without that beneficial trait.
Understand how evolution explains: Why populations change.
Why there are so many different kinds of organisms on Earth.
Why some organisms that look alike are only distantly related.
Why some organisms that look very different are actually closely related?
Know that both Darwin and Wallace developed the theory of evolution by natural selection at the same time.
Check Your Understanding
What does the word evolution refer to when used in day to day conversations?
What does biological evolution mean?
Who primarily proposed the theory of evolution by natural selection?
Introduction
Biological evolution is change in species over time. The idea of evolution was proposed by many people before Charles Darwin (Figure below) began collecting evidence for the idea. Scientists for hundreds of years had hypothesized that species change over time. But it was not until Darwin published his research and detailed analysis that the idea of evolution started to gain widespread acceptance. Darwin’s theory of evolution by natural selection brings all fields of biology together and illuminates nearly every aspect of biology. As one famous biologist said, "Nothing in biology makes sense except in the light of evolution."
Figure 7.1
Charles Darwin was one of the most influential scientists who has ever lived. Darwin introduced the world to the theory of evolution by natural selection, which laid the foundation for how we understand the living world today.
Evolution by natural selection explains:
The tremendous variety of organisms on Earth.
Why some organisms that resemble each other are distantly related.
Why some organisms that do not resemble each other are closely related.
There are three parts to Darwin’s Theory of Evolution by Natural Selection.
Evolution, which is change in species over multiple generations (Figure below).
Natural selection, in which individuals of a population that are most likely to survive and reproduce are also most likely to pass on traits that have a genetic basis to any offspring.
Adaptation, which are traits that help a plant or animal survive and reproduce in a particular environment. Adaptations are the result of natural selection. For example, light-colored moths on dark trees might be easier for birds to see and catch than dark moths on dark-colored trees. If the moths' color has a genetic basis, then after many generations of birds catching more light moths than dark moths, the population of moths will consist mostly of dark moths.
Figure 7.2
Humans and the other apes in this drawing all evolved from a common apelike ancestor.
In everyday English, "evolution" simply means to "change" or a "stepwise change from simple to complex." In biology, evolution means change in the inherited traits of a group of organisms over multiple generations (Figure below). Biological evolution has changed biologists' understanding of all life on Earth.
Figure 7.3
Human earlobes may be free or attached. You inherited the particular shape of your earlobes from your parents. Inherited traits are influ
enced by genes, which are passed on to offspring and future generations. Your summer tan is not passed on to your offspring. Natural selection only operates on traits like earlobe shape that have a genetic basis, not on traits like a summer tan that are "acquired."
Darwin’s Observations
Most people in the world did not become aware of the theory of evolution until 1859, when Charles Darwin published his book On the Origin of Species by Means of Natural Selection. This book described the observations and evidence that he collected over 20 years of intensive research, beginning with a five-year voyage around the world on a British research ship, the HMS Beagle. During this five-year voyage (Figure below), Darwin was able to make observations about plants and animals spread around the world, and to collect specimens to study when he returned to England. Each time the Beagle stopped at a port to do some trading, Darwin went on land to explore and look for the local plants, animals, and fossils. One of the most important things Darwin did was to keep a diary. He took extremely detailed notes and drawings about everything he saw as well as his thoughts.
Figure 7.4
Charles Darwins famous five year voyage was aboard the from 1831-1836.
The Galápagos Islands
The around the world voyage of the HMS Beagle was mostly to map the coastline of South America. Darwin’s best known discoveries were made on the Galápagos Islands (Figure below), a group of 16 volcanic islands near the equator about 600 miles from the west coast of South America. Darwin was able to spend months on foot exploring the islands. Darwin’s Theory of Evolution by Natural Selection was a result of his observations and over 20 years of examining the specimens he had collected and sent back to England, many of which came from these islands.
Figure 7.5
The Galpagos Islands are a group of 16 volcanic islands 972 km off the west coast of South America. The islands are famous for their many species found nowhere else.
Darwin was amazed by the array of life he saw on the Galápagos Islands. He saw animals unlike anything he had ever seen before. Darwin was struck by how the same kind of animal differed from one island to another. For example, the iguanas (large lizards) differed between islands (Figure below). The members of one iguana species spent much of their time swimming and diving underwater for seaweed, while those of another iguana species lived on land and ate cactus. In England, he was accustomed to watching cormorants fly, so he was surprised to find flightless cormorants on the islands alongside flying cormorants.
Figure 7.6
The Galpagos land iguanas are among the signature animals of the Galpagos Islands.
Giant Tortoises
Giant tortoises (Figure below), large enough for two men to ride on, plodded across the islands and foraged on super tough leaves. Some of the tortoise species were found on only one island. Darwin was fascinated by the number of ways that organisms were well-suited to their environments. Even the tortoise shells were specially adapted to the conditions. Tortoises that ate plants near the ground had rounded shells, while the tortoises that stretched their necks to reach plants higher in shrubs had shells that bent upwards, allowing them to stretch their necks upward (Figure below).
Figure 7.7
The name Galpagos means giant tortoise. When Darwin arrived on the Galpagos Islands, he was amazed by the size and variety of shapes of these animals. The giant tortoise is a unique animal found only in the Galpagos Islands. There are only about 200 tortoises remaining on these islands.
Figure 7.8
This tortoise is able to reach leaves high in shrubs with its long neck and curved shell.
Darwin's Finches
The most extensively studied animals on the Galápagos are the finch species (birds) (Figure below). When Darwin first observed the finches on the islands, he did not even realize they were all finches. But when he studied them further, he realized they were all the same type of bird, and that each island had its own distinct species of finch. The birds on different islands had many similarities, but their beaks differed in size and shape.
Figure 7.9
Four of Darwins finch species from the Galpagos Islands. The birds came from the same finch ancestor. They evolved as they adapted to different food resources on different islands. The first bird uses its large beak to crack open and eat large seeds. Bird #3 is able to pull small seeds out of small spaces.
In his diary, Darwin pointed out how each animal is well-suited for its particular environment. The shapes of the finch’s beaks on each island were well-matched with the seeds available on their particular island, but not the seeds on other islands. A larger and stronger beak was needed to break open large seeds and a small beak was needed to feed on some of the smallest seeds.
Darwin also noticed how different species were distributed around the world. The finch, tortoise and other species found on the Galápagos Islands were similar to species on South America, the nearest continent. Yet they also differed. Likewise, species he saw on islands near Africa were similar to, but different from species on Africa.
Return to England
When Darwin returned to England five years later, he did not rush to announce his discoveries. Unlike other naturalists before him, Darwin did not want to present any ideas unless he had strong evidence supporting them. Instead, once Darwin returned to England, he spent over twenty years examining specimens, talking with other scientists and collecting more information before he presented his theories. Darwin’s observations eventually resulted in the Theory of Evolution by Natural Selection. His now famous book, The Origin of Species is a diary of his explorations and discussion on how he interpreted his observations (Figure below).
Figure 7.10
Charles Darwin presented the Theory of Evolution by Natural Selection in this book. The theories were based on evidence he collected and tested.
Other Influences on Darwin
How did Darwin come up with his theories? Some of Darwin’s idea conflicted with widely held beliefs, included those from religious leaders, such as:
All organisms never change and never go extinct, they are fixed.
The world is only about 6,000 years old.
It was because of these widely held beliefs that Darwin delayed in presenting his findings.
Charles Darwin was influenced by the ideas of several people.
Before his voyage on the Beagle:
Jean-Baptiste Lamarck proposed the idea that evolution occurs. However, Darwin differed with Lamarck on several other points. Lamarck proposed that traits acquired during one’s lifetime could be passed to the next generation.
Darwin’s grandfather, Erasmus Darwin, wrote a book called Zoonomia. Charles Darwin was influenced by many of his grandfather’s ideas including his descriptions of how species change (evolve) through artificial selection. During artificial selection, people choose specific traits to pass to the next generation, such as with horse or dog breeding (see below).
Charles Lyell, a well-known geologist and one of Darwin’s instructors. Darwin learned about geology, paleontology and the changing Earth from Lyell. These findings suggested the Earth must be much older than 6,000 years.
Thomas Malthus: Darwin’s ideas of natural selection were inspired by reading an essay by Thomas Malthus, an economist who suggested that humans could overpopulate and potentially exhaust food supplies. Darwin thought this must be especially true for animals, as they have a tendency to have more offspring than people have. There would therefore be a competition for survival.
Charles Darwin came upon some of his ideas about natural selection and adaptations from reading about artificial selection and breeding dogs. All dogs, from Chihuahuas to St. Bernards are part of the same genus as wolves (Canis lupus). Humans created the different breeds of dogs by selecting dogs with specific traits to breed together. For example, greyhounds were created by selecting the fastest runners and breeding them together (Figure below).
After the Voyage of the Beagle: Alfred Russel Wallace, another naturalist, a
lso developed a theory of evolution by natural selection. Alfred Wallace toured South America and came up with a very similar theory of evolution by natural selection at the same time that Darwin did. Darwin and Wallace presented their theories and evidence in public together. Because of the vastness of Darwin’s data, and his book, he is mostly credited and associated with this theory.
Figure 7.11
Darwins grandfather had a big influence on Darwins ideas by introducing him to artificial selection of dogs and horses. Humans have created hundreds of dog breeds by selecting which dogs to breed based on certain features, such as size, coloration, speed, or facial features.
Natural Selection and Adaptation
The Theory of Evolution by Natural Selection means that the inherited traits of a population change over time through natural selection. Inherited traits are features that are passed from one generation to the next. For example, your eye color is an inherited trait (you inherited from your parents). Acquired traits are features such as strong muscles from working out.