Thursday Forum : Random Science
Related Books
Investigating Disease Patterns:
The Science of Epidemics
Paul D. Stolley & Tamar Lasky
Get a Grip on Evolution
David Burne
Plague’s Progress
Arno Karlen
Related Webpages
PBS evolution website
http://www.pbs.org/wgbh/evolution/
PBS Darwin Website
http://www.pbs.org/wgbh/evolution/darwin/index.html
----------------------------------------------------------------------------------------------------------------------------- -Neo-Darwinism
The modern evolutionary theory, or neo-Darwinism, brings together Charles Darwin's theory of the
evolution of species by natural selection with Gregor Mendel's theory of genetics as the basis for biological
inheritance.
It introduced the connection between two the important discoveries; the units of evolution.
With the discovery of DNA & its form of replication, Neo-Darwnism could explain genetic variation in
populations through chance mutations ( mistakes in DNA replication) and recombination (mistakes in the
chromosomes during the formation of sperm & egg cells).
Evolution consists primarily of changes in the frequencies of alleles (different forms of genes) between one
generation and another.
Speciation occurs gradually when populations are reproductively isolated by geographic barriers.
What can cause mistakes in DNA replication?
a) Chance (The system is not prefect)
It is possible that the replication process makes mistakes were made along the way -- in other
words, that a base pair in one DNA molecule doesn't match the corresponding pair in the other molecule.
On average, one mistake may exist in every billion base pairs. That's the same as typing out the entire
Encyclopedia Britannica five times and typing in a wrong letter only once!
b) Radiation
DNA readily absorbs UV-B radiation, which commonly changes the shape of the molecule in one of
several ways. The illustration below illustrates one such change in shape due to exposure to UV-B
radiation. Changes in the DNA molecule often mean that protein-building enzymes cannot “read” the DNA
code at that point on the molecule. As a result, distorted proteins can be made, or cells can die.
c) Viruses
Viruses could change genetic information in our DNA
EPIDEMIOLOGY
Epidemiology in its broadest sense is the study of disease patterns in human populations.
It is the study of how often disease occurs in different groups of people and why. Information about
epidemics is used to plan and evaluate strategies to prevent illness and to guide the management of
patients who already have the disease.
An epidemic is generally a widespread disease that affects many individuals in a population. An epidemic
may be restricted to one locale or may even be global (pandemic). An outbreak of a disease is defined as
being epidemic, however, not by how many members or what proportion of the population it infects but by
how fast it is growing.
The Beginnings of Epidemiology
Dr. John Snow is famous for the suppression of an 1854 outbreak of cholera in London's Soho district. He
identified the cause of the outbreak as a public water pump in Broad Street, and had the handle removed,
thus ending the outbreak.
This was a major event in the history of public health, and can be regarded as the founding event of the
science of epidemiology.
SCREENING FOR DISEASE
One way to catch a disease before it hits epidemic proportions is to screen for the disease.
Why isn't everyone screened?
Example In a population of 100,000 people, 1 person in a 1000 has a particular disease. If a screening test
has a false positive rate of 5%, then about what percent of those who test positive will actually have the
disease (Even if all those who have the disease are caught by the screening)?
Possible Answers
a) 1%
b) 2%
c) 5%
d) 80% e) 95%
f)99%
The answer is 2%; 98% of those who test positive will not have the disease. So unless you think that a
large percent of the people you screen could have a particular disease you should not really screen.
Measuring the accuracy of a Screening Method
Sensitivity is the percent who actually have the disease which the screening test catches.
Specificity is the percent who don't have the disease
and the test says that they do not
Positive Predictive value is the percent of those who tested positive for the disease who really do have
the disease.
Negative Predictive value is the percent of those who tested negative for the disease who really do not
have the disease.