Transcript Overview of Genetic Science Dr. Mike Dougherty Department

Overview of Basic Genetic Science
Dr. Mike Dougherty
Department of Biology
Hampden-Sydney College
What is science and how does it differ from other
ways of knowing the world?
Scientific understanding relies on:
Logic
Evidence
Naturalism
Tentativeness and falsifiability
Science rejects:
Supernatural explanations
Arguments from authority
Methodological Materialism
What are “genes” and how
do they work?
DNA is an information molecule with two functions:
1. storage and copying (i.e., inheritance)
2. expression (i.e., physiology, health, disease)
Each DNA strand serves as a
template for its own replication,
ensuring continuity of
information.
Pedigrees illustrate how information can be passed on to the next
generation of family members through inheritance.
Gene expression
Linear and causal links exist
between DNA and proteins.
Proteins are the workhorses of
cells and tissues.
Step 1:
Recognizing a gene.
Step 2:
Production of an RNA,
a molecule that bridges
the chemical gap
between DNA and
protein.
Step 3:
Translating the
language of RNA
(nucleic acid) into the
language of proteins
(amino acids).
The Genetic Code
Why are proteins so important?
Chain of causation:
DNA sequence
RNA sequence
amino acid sequence
folded structure
function
If proteins carry out the functions of cells and
tissues, does that mean they control traits, such
as height, heart disease, and happiness?
NOT by themselves!
It is more accurate to say that “genes influence traits”
to varying degrees?
Phenotypes (traits) exist on a continuum:
Strong environmental
influence
Weak environmental
influence
Personality
Major depression
Heart disease
Phenylketonuria
Weak genetic
Strong genetic
influence
influence
Genetic variation
Humans have the same genes,
but those genes exist in
different versions.
These differences help explain
why many people with the same
disease manifest symptoms in
unique ways.
These differences also reveal
evolutionary connections among
related species.
How does DNA sequence variation arise?
Through environmental
insults to DNA and
mistakes during copying.
Mutations can alter proteins, which
may lead to normal trait variations
or disease.
But . . . in many cases the
mutations are harmless.
Can we predict a person’s traits if we
know their DNA sequence?
Only in rare cases . . .
If a genotype is highly penetrant, we can often
predict accurately that a person will develop
certain traits (usually diseases), but the degree
of the trait is highly variable and unpredictable.
(e.g., Huntington’s disease)
As it turns out, most genotypes . . .
. . . are NOT highly penetrant.
e.g., familial colon cancer
65% of persons having the
mutated gene will develop
cancerous polyps, but we
cannot predict whether any
given individual will be
affected or disease-free.
Even worse (for prediction),
most traits are not strongly
influenced by a single gene.
They are polygenic and
multifactorial.
e.g., height, skin
color, personality
traits, heart disease,
diabetes.
Such traits are said to show
continuous variation.