What is Science?

What is Science?

• A way of knowing

• Based on repeatability

• Based on coming up with the most plausible answer from a suite of possible answers.

• A process of going from singular propositions to general propositions.

Theory

Law

Rule

Model

Hypothesis

Auxiliary Hypothesis

Ad hoc Hypothesis

Working Hypothesis

FactSingular proposition

General Proposition

Important concept.

• How many ways can two things be identical?

• How many ways can two things be different?

Justificationism

Falsificationism

The Process of Science

• Observation – • Question – (Induction)• Logic – if ... then... (Deduction)• Hypothesis – H

0 (no difference between observed and

expected) and H1 (observed and expected are different)

• Experiment – • Result – reject or accept hypothesis• alternative hypotheses

• Remember proof in science is impossible

Where does the genetic information reside?

• karyotype

-DNA discovered in 1869 by Friedrich Miescher, a German Chemist. Extracted from the nucleus. -Walther Flemming described the chromosomes in 1882

Discovery of chromosomes and DNA

But this is not evidence that genes are on chromosomes?

Observations:Do both parents contribute equally to

offspring?• What can we observe?

– Casual observations—children often resemble parents, sometimes their mother, other times their father

– Controlled crosses—when the same cross is set up twice, switching the sex of the parent, the results are the same.

What is in a typical egg? What is in a typical sperm?

• Eggs

• Sperm

• genetic information -> CHROMOSOMES

One egg, many sperm

Griffith 1928 Streptococcus pneumoniae

• The ‘transforming principle’ of Griffith, using ‘Rough’ and ‘Smooth’ bacteria in 1928

R strain

S strain

Hammerling Exp.

Hershey-Chase Experiment

The Science behind the discovery that the genetic material resides in the chromosomes

• Observation – offspring inherit traits from their parents.• Question – where does the information reside

responsible for traits?• Observation - the nucleus appears to be important.• Logic – if we remove the nucleus from a cell it will not

divide and grow• Hypothesis – the nucleus contains the hereditary

information• Null Hypothesis – Removal of the nucleus from a cell

will not affect development• Experiment – remove or kill nucleus • Result – cell does not develop – reject null hypothesis.

Timeline

• 1857 - Darwin - Characteristics of parents passed on to young.

• 1869 – Friedrich Miescher – discovered ‘nuclein’ (DNA)

• 1882 – Walther Flemming – Chromosomes• 1928 – Griffith – transforming principle• 1930’s – Hammerling – Acetabularia nucleus• 1952 – Hershey-Chase Experiment• 1952 – Briggs and King – nuclear transplant exp. in

frogs