Transcript Evolution and Medicine

EVOLUTION AND MEDICINE
There is no question that evolution is the major unifying concept in
biology and that “nothing in biology makes sense except in the light
of evolution”. (Dobzhansky,1973)
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EVOLUTIONS GREATEST BENEFITS WILL BE TO
PROVIDE A THEORETICAL FRAMEWORK FOR
UNDERSTANDING:
• Why organisms are vulnerable to disease
• How infectious agents evolve
• How common ancestry helps scientists use the results from animal models to
understand issues related to human health
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• Use scientific inquiry to try to understand two fundamental
observations about living organisms:
• Diversity
• Evolution
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EVOLUTION
• Refers to change
• Changes refers specifically to a change in allele frequencies in a
population; this is heritable and occurs over successive generations.
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MAJOR QUESTIONS EVOLUTIONARY BIOLOGIST ASK:
1. What mechanism of evolution caused a change in a lineage or trait?
2. What is the evolutionary history, or phylogeny, of a living lineage or a specific
trait?
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1.1 PROCESS OF EVOLUTION
• Descent as in “descent with modification” emphasizes the history of
lineages.
• Modification refers to that lineages change over time.
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CAUSES IN CHANGE?
Four different mechanisms:
1) mutation
2) gene flow (migration)
3) genetic drift
4) natural selection
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MUTATION
ALL genetic variation arises from mutation.
Genetic recombination reshuffling existing variation.
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GENE FLOW
Also known as migration, is the movement of alleles from one population into
another through immigration and emigration of individuals.
Typically reduces genetic differences.
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GENETIC DRIFT
Random changes in allele frequencies due to chance or sampling error.
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NATURAL SELECTION
Proposed by Alfred Wallace and Darwin
1) Individuals in a population vary for characteristics.
2) Inheritable traits
3) Individuals with certain traits have more children than others
Conclusion: Individuals that possess heritable traits that enable them to better survive
and reproduce will leave more offspring and these traits will increase in frequency over
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future generations.
NATURAL SELECTION
• Natural Selection: A process that can cause evolution. This process can result in adaptations. It can be
summarized as five principles:
• 1. variation: Individuals within a population vary in many traits, including physical and biochemical traits.
• 2. inheritance: Some of the differences in traits among individuals can be passed from parents to offspring.
(Some variation is heritable.)
• 3. origin of variation: Some of the variation in traits among individuals has a genetic basis. This variation
originated, often many generations ago, as mutations—changes in the genetic information that are random
with respect to the needs of the organism.
• 4. fitness: Both the environment and the traits that individuals possess affect survival and reproduction.
Individuals with heritable traits that enable them to better survive and reproduce in a particular
environment will leave relatively more offspring.
• 5. evolutionary change in populations: The frequency of traits and the alleles that affect those traits change
in a population over time.
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1.2 COMMON ANCESTRY
Evolutionary trees (phylogenies): summary of the history of the relationship
among organisms.
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• Alleles associated with specific phenotypes are more frequent in different geographical
origin populations. (i.e. Ashkenazi Jewish have higher frequency of BRCA 1 and 2).
• So if ancestry is known, scientist/ doctors can provide specific genetic conditions which
may influence genetic testing.
• The evolutionary origin of pathogens is now routinely investigated by using phylogenetic
methods.
• Phylogenetic analysis has been used to determine 2 types of HIV, SARS, and that bats are
the reservoir for coronavirus.
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• What is Staphylococcus aureus?
• Staphylococcus aureus is a species of bacterium. This species is often called “staph.”
These bacteria are spherical in shape and sometimes form clusters that look like grapes
(see Figure 1). These bacteria are commonly found on the skin or in the nose of
healthy people. They are also found on other animals, such as cows, pigs, and chickens.
About one in three people have populations of S. aureus in their nose. In most cases,
this does not cause any illness. But sometimes, S. aureus does cause infections. While
most are minor skin infections, some are serious, especially if the bacteria get into the
body through a wound, such as a cut. They are frequent causes of infections after
surgery, bloodstream infections, and pneumonia. Like other bacteria, S. aureus
reproduce by binary fission. When an S. aureus cell divides, it produces two daughter
cells that have the same genetic instructions. However, mutation introduces genetic
variation into a population of bacteria.
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STAPH AUREUS
Figure 1. Staphylococcus
aureus. These bacteria are
about 1/1,000th millimeter in
diameter. If lined up in single
file, more than 25,000 of
them would be 2.5
centimeters (1 inch) long.
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WHAT IS MRSA?
• https://www.youtube.com/watch?v=_7qLlRHxQO4
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• https://www.youtube.com/watch?v=6YFLkRlZzXw
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• MRSA Outbreak ??
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Staph Infection Popping Up Across North Carolina
It's a common bacteria found on millions of people, but a resistant form of staph infection called MRSA has been popping up across North Carolina. It is
blamed in the death of a Virginia teenager.
A handful of cases were confirmed in Buncombe, Mecklenburg, Forsyth, Guilford, Orange, Northampton, Cumberland, Robeson and Duplin counties. State
health officials stressed that the cases do not constitute an outbreak, however.
The most recent MRSA case was detected in Northampton County at Willis Hare Elementary School in Pendleton. Officials declined to identify whether it was
a student or a staff member who was infected.
The school district was following protocols established by the state Division of Public Health to contain the infection, officials said. Hand sanitizers were
provided in classrooms, and an extra janitor was assigned to the school to provide additional cleaning in the cafeteria and other common areas.
Letters were sent to the parents of the students in the elementary school, and an automated telephone message was sent Thursday night to the parents and
school staff. No schools were expected to close because of the infection, officials said.
Another case of MRSA was also confirmed in a student-athlete at Purnell Swett High School in Robeson County. School officials sent out a letter Friday to
parents explaining the situation. They also cleaned the locker room and areas where students might have been exposed. WRAL contacted school districts
across the viewing area, and all were taking extra precautions to make sure campuses were clean. They've also informed students and staff about ways to
protect themselves.
Cumberland County was handling five cases of MRSA. In the past three weeks, five inmates at the local jail were infected. Two remain at the facility, and three
were transported to a hospital for treatment. The detention center was conducting a staph-infection-awareness class for all employees
Hospitals are also a common place for the MRSA bacteria. Studies show more than 126,000 hospitalized patients are infected each year. As of Friday, UNC
Hospitals said 55 percent of its patients with skin infections had MRSA.
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The germ has been called a Super Bug because of its resilience. Numbers on how widespread it is in North Carolina were hard to come by
because doctors and hospitals do not have to report cases to the state.
Also, it can often be confused with other infections. One Orange County man quickly found out this was something different, however. Monroe
Thompson, an electrician in Hillsborough, was at work when he noticed the red, tender bump on his hand about five months ago.
“First, I thought it was a spider bite. That’s what all the people told me. ‘You got a spider bite. You got a spider bite,’” he said.
The bump looked like a large boil or pimple.
“And it kept getting worse and worse and worse, and that’s when I figure I better do something,” Thompson said.
He checked into an emergency room when he had a fever of 104, and he had to stay several days. Doctors found he had MRSA. “I kind of felt like
I was coming down with the flu when I had the fever,” he said. Thompson was given antibiotics, which he said helped clear it up in a couple of
weeks. He said his doctor suggested that he pour a bottle cap full of Clorox in his bathwater to kill germs. Thompson, who still wears a scar on
his hand, said he has no idea where he got it. Hospitals are a common source, but it could be anywhere.
“It can occur among sports teams, close contact, school, military recruits – anywhere there are crowds and people have close contact,” said Dr.
David Weber, a physician at UNC Hospitals.
Weber said most patients admitted for staph infections have what's known as community-associated MRSA. It's acquired by otherwise healthy
people who are not infected at hospitals.
“This has dramatically increased over the last two or three years compared to five or 10 years ago,” Weber said. Linda Shambley, also of
Hillsborough, said she has had at least six staph infections since July and thinks she might have gotten them from a hospital stay. Her doctor told
her it was not MRSA, but now she's taking extra precautions.
“Now I’m even scared to go in the public bathroom,” Shambley said. Around her home, she tries to keep everything as clean as possible. “As
soon as I come in, I go and wash my hands with anti-bacterial soap, because I don’t want to catch this stuff again.”
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• Has anyone been affected by MRSA or know anyone that has been affected by MRSA?
• Are you willing to share your story?
• http://www.ncbi.nlm.nih.gov/pubmed/15689585
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CLASSWORK
1. Researcher developed the antibiotic methicillin to treat people with
infections of S. aureus that are resistant to penicillin. Within two years,
populations of S. aureus that were resistant to methicillin started showing up
in hospitals. How would a scientists explain how the change may have
occurred in S. aureus populations?
2. How can the study of evolution (such as the adaptation of bacterial
populations to an antibiotic) help researchers improve people’s health?
EXPLAIN your initial ideas.
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PRIOR CONCEPTIONS ABOUT EVOLUTION
Evolution is Only a Theory
Acquired Characteristics can be Inherited
Species have an underlying nature that Cannot change
Natural Selection leads to perfection
Fitness means individuals are stronger or more athletic
Natural selection and evolution mean the same thing
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Evolution is Only a Theory
In science a theory is an explanation or model based on observation,
experimentation, and reasoning, especially one that has been tested and confirmed
as a general principle helping to explain and predict natural phenomena; not a hunch
or guess
Acquired Characteristics can be Inherited
Only genetic based characteristics can be passed along.
Species have an underlying nature that Cannot change
There is variation within species which can lead to change over time.
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Natural Selection leads to perfection
Species adapt to conditions in the present, but these conditions change. Adapt to
survive current environment.
Fitness means individuals are stronger or more athletic
Cooperation is an essential aspect for survival.
Natural selection and evolution mean the same thing
There are multiple mechanisms for evolution with natural selection being just one
of them.
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ANCESTRY TREE THINKING
• True understanding of biodiversity shows that all species existing today are descended
from ancestors that have survived from 3.5 billion years ago.
• Plants, worms, bacteria, and humans all descend from survivors whom survived
multiple mass extinctions and major environmental challenges.
• To claim one existing group is “more highly evolved” than another ignores this fact.
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 Modern Species Are Ancestors: One way this misconception is manifest is the saying “humans
evolved from chimpanzees.” Instead, humans and chimpanzees evolved from a common ancestor.
This common ancestor may have shared characteristics with modern chimpanzees, but both the
modern chimpanzee lineage and the lineage that led to humans have been evolving for the same
amount of time since splitting from the common ancestor (Baum et al., 2005).
 The Ordering of Species at the Tips of an Evolutionary Tree Is Always Meaningful: People do not
recognize that the most closely related species are those that share the most recent common
ancestor (Baum et al., 2005).
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FEATURED EXAMPLES OF EVOLUTION AND MEDICINE
• The evolution of antibiotic-resistant bacteria is a classic example of evolution by
natural selection that has large impacts on humans.
• MRSA is a major abx-resistant bacteria
• It is not yet clear if community-acquired MRSA evolved from hospital-acquired MRSA
or if it evolved from different strains of Staphylococcus aureus.
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• Researchers at NIH used genetic sequences and an analysis tool called an “evoprint” to
demonstrate that a strain of hospital-acquired MRSA shares multiple DNA sequence blocks
with Listeria monocytogenes and Staphylococcus saprophyticus (Brody et al., 2008). Both of
these bacteria can also cause bovine mastitis. These data suggest that bacterial co-infections
may be an important factor in the evolution of resistance.
• Evoprint – a diagram that summarizes the similarities and differences in a genetic sequence
for multiple species.
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PAX6
Gene that plays a crucial role in regulating the growth of eyes
It is found on chromosome 11 and spans over 20,000 nucleotides.
Can be found in humans, fruit flies, zebrafish, mice, squid, planarians, and even ribbon
worms.
Studies on Pax6 support the claim that new, complex structures are rarely built anew
throughout evolution; rather, they are often assembled from preexisting structures.
Some mutations to the Pax6 gene cause the human disease aniridia. Scientists have
identified over 250 such mutations in humans.
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CLASSWORK
• Worksheets – due at end of class
• Pg. 175 online book
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