Download - 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
DNA is an information molecule with two functions:
1. storage and copying (i.e., inheritance)
2. expression (i.e., physiology, health, disease)
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.
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?
It is more accurate to say that “genes influence traits” to varying degrees?
Phenotypes (traits) exist on a continuum:
Weak genetic Strong genetic
influence influence
Personality Major depression
Heart disease Phenylketonuria
Strong environmental Weak environmental influence influence
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.
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.