Basics of genetics. Important for B.SC and M.SC. students

1. DISCOVERY OF DNA AS THE
UNIVERSAL GENETIC MATERIAL
B Y: R U P A L A G R A W A L
L E C T U R E R : N I D H I M A M

2. THE SHORT HISTORY OF DNA AND
GENETICS (PART 1)
From 1866-1953

3. SEARCHING FOR GENETIC
MATERIAL
Gregor Mendel
(1866):
discovered that
inherited traits are
determined by discrete
units, or 'genes,’ -
passed on from the
parents.
Freidrich
Miescher(1868):
discovered DNA
Isolated something new
from the nuclei of
eukaryotic cells
 Later called DNA!!!

4. SEARCHING FOR GENETIC
MATERIAL
Thomas Hunt Morgan (1910):
Worked with fruit flies
Specifically eye color of these flies!
Discovered genes are located
(linked) on chromosomes

5. SEARCHING FOR GENETIC
MATERIAL
Fredrick Griffith (1928):
Studied effects of
virulent (virus-causing)
bacteria vs. nonvirulent
bacteria injected into
mice
Used transformation:
Inserted foreign DNA and
changed protein/ trait
believed that the
transforming agent
was an inheritance
molecule.

6. GRIFFITH'S TRANSFORMATION
EXPERIMENT
Used the Pneumococcus bacteria
Include2 types:
a virulent S strain with a Smooth coat
kills mice
a non-virulent R Rough strain
does not kill mice.
Heat destroys (kills) living cells!!!
When heated Smooth (harmful) cells (DEAD) are
mixed with living Rough (benign) cells and
injected into mice, the mouse dies.
WHY?
http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_Experim
ent.swf

7. NON-VIRULENT VS.
VIRULENT
BACTERIA
SMOOTH:
kill
ROUGH:
harmless

8. BAD/HARMFUL
NOT
HARMFUL/BENIGN

9. SEARCHING FOR GENETIC
MATERIAL
http://brookings.k12.sd.us/biology/ch12DNARNA/Chapter%2012A.mpg

10. SEARCHING FOR GENETIC
MATERIAL
• Oswald Avery, Colin MacLeod, & Maclyn
McCarty (1944):
Reported that “transforming
agent” in Griffith's experiment
was DNA.
Also used the Pneumococcus
bacteria and test tubes (NOT mice)

11. DNA is the Molecule of Heredity.
When various isolated
chemical components
of the S-strain
Pneumococcus cells
was mixed the R-strain
Pneumococcus cells, it
was shown that the
DNA from the S-strain
cells, that caused trans-
formation.

14. THE AVERY, ET AL. EXPERIMENT
Used S (harmful) strain
 Opened up the cells
 Isolated
 DNA, proteins and other materials SEPERATELY
 Mixed R bacteria with these different materials
 Only those mixed with DNA were transformed into S bacteria.
S DNA
+
R Bacteria

S PROTEINS
+
R Bacteria

TEST
TUBE
S
OTHER S
CELL PARTS
(sugar/RNA)
+
R Bacteria


15. CONCLUSION
• Removal of all protein from the transforming material
did not destroy its ability to transform R strain cells.
• DNA digesting enzymes destroyed all transforming
ability. The transforming material is DNA.
• Avery et al (1944) concluded that:
1. Active factor is DNA which can cause transformation
2. SIII strain contains the active factor

16. 16
Experiment of Hershey and Chase
Alfred Hershey and Martha Chase demonstrated the genetic
material is DNA by using viruses that infect bacteria. These
viruses only stay on the outside of the cell when infecting the
cells. Also viruses are composed of protein and DNA. It is
known that the virus injects its genetic material into the
bacterium which had to DNA or proteins.
Experiment of Hershey and ChaseExperiment of Hershey and ChaseExperiment of Hershey and Chase

17. LIFE CYCLE OF BACTERIOPHAGE

18. EXPERIMENT WITH T2 BACTERIOPHAGE

19. 19
Experiment of Hershey and Chase

20. CONCLUSION:
• As Coat of bacteriophage labelled with S35 so the
results clearly indicate that only DNA enter into the
host cell& protein coat left outside.
• The DNA entering the host cell carries all the
genetic information for synthesis of new phage
particle.
• This proves that DNA is the genetic material in
bacteriophage.