Bio.: Geneticists

1. T. H. Morgan
-observed eye colors of fruit flies

Cross	Outcome
Cross	Expected Phenotypes	Observed Phenotypes
P₁ Red ♀ × P₁ White ♂	F₁ = All Red	F₁ = All Red*
F₁ Red ♀ × F₁ Red ♂	75% Red ♀ and ♂ 25% White ♀ and ♂	50% Red ♀ 25% Red ♂ 25% White ♂

Reference: http://www.nature.com/scitable/topicpage/thomas-hunt-morgan-and-sex-linkage-452
-all white-eyed flies were males
-the white-eye allele is recessive and is located on the X chromosome
-Males have white eyes because they only have 1 X chromosome. If the white-eye allele is inherited, it becomes dominant. (Well, not exactly dominant. But that's the only allele for eye color it has, right?)
Theories:
i. Genes are located on chromosomes
ii. Either protein or DNA codes for the genetic information

2. Hershey and Chase
The experiment:
Purpose: To illustrate the relation between DNA and heredity and to demonstrate that DNA is the genetic material
Procedure:
i. Allow phages to attack a bacterial cell. Their proteins are radioactively labelled.
ii. Allow a second group of phages to infect a bacterial cell. Their DNA is radioactively labelled.
Result:
i. Phages produced by the 1st cell were not radioactive.
ii. Phages produced by the 2nd cell were radioactive

Conclusion:
DNA is the genetic material that is passed from generation to generation.
check this out!!
http://highered.mcgraw-hill.com/olc/dl/120076/bio21.swf

3. Frederick Griffith
The experiment of transformation:
R strain --> rough --> harmless
S strain --> smooth --> fetal
Procedure:
Inject the strain(s) into mice
Trial 1: S strain is injected
Trial 2: R strain is injected
Trial 3: S strain is killed (by heat) and injected
Trial 4: Dead S strain and alive R strain are injected
Hypothesis:
Trial 1: The mouse would die.
Trial 2: The mouse would live.
Trial 3: The mouse would live.
*Trial 4: The mouse would live.
Results:
Trial 1: The mouse died.
Trial 2: The mouse lived.
Trial 3: The mouse lived.
*Trial 4: The mouse died.
Conclusion:
The injection caused a change in genotype and phenotype. This process is called transformation.

4. Erwin Chargaff
-discovered the 4 bases of DNA
Purines (double-ringed): adenine, guanine
Pyrimidines (single-ringed): thymine, cytosine
% T = % A
% G = % C
Each species has a distinct DNA composition.