1. CLASSICAL AND
MODERN GENETICS
Great Idea:
All living things use the same genetic code
to guide the chemical reactions in every cell.

2. OUTLINE
 Classical Genetics
 DNA and the Birth of Molecular Genetics
 The Genetic Code

3. CLASSICAL
GENETICS

4. Part 1 Classical Genetics
Genetics got it’s start as the study of
inheritance.
Charles Darwin proposed that favorable traits
could be passed from generation to generation
resulting in natural selection.
However, Darwin did not know how these
traits were passed on.

5. Chromosomes from the Indian muntjak

6. It remained for
the Austrian
monk Gregor
Mendel, in 1865,
to carry out the
definitive
experiments.

7. Mendel crossed tall and dwarf pea plants: all offspring
were tall.
Tall Dwarf
x
F1
tall

8. Next, Mendel crossed some of these F1 plants among
themselves. Of these offspring (the F2 generation), about
3/4 of the plants were tall and 1/4 were dwarf.
tall tall
x
F2 tall tall tall dwarf

9. Mendel tested 6 other traits of pea plants:
traits for seed shape (wrinkled or smooth)
seed color (yellow or green), etc.
In each case, all of the F1 plants looked as
though they had inherited the trait of just one
of their two parents, but in the F2 generation
both traits always appeared -- and always in a
3 to 1 ratio.

10. The trait which was expressed in the F1 generation
was always about 3 times as numerous in the F2
generation as was the other one which was hidden
in the F1's.

11. Homozygous = same
Heterzygous = different
When both alleles for a trait are identical, say that the organism
is homozygous for that trait. When the 2 alleles are different, is
heterozygous.
TT = Homozygous Tt = Heterozygous
tall tall
Tall is dominant over dwarf; dwarf is said to be a recessive trait
(i.e. can only be expressed when there are two copies of it).

12. Homozygous = same Heterzygous =different
Tall Dwarf Tall
TT tt Tt

13. Mendel's original cross produced only tall
offspring:

14. However, in the second generation the rules of
probability dictate that 1/4 of the plants will be tt =
dwarf and 3/4 will have at least one T and hence
be tall.

15. Mendel Studied Many Traits in Pea Plants--
Seed shape- smooth or wrinkled
Seed color- green or yellow
Pod shape- smooth or bumpy
Pod color- green or yellow
Flower location- at leaf or tip of branch

16. Many traits are passed on by genes.
The genes encode the information for proteins.
The genes are segments of DNA.
Mendel found that two factors determine traits.
These are alternate forms of genes- one from each
parent.
These are now called alleles.

17. CLASSICAL GENETICS
 Mendel
 Basic laws of inheritance
 Classic pea plant experiments
 Purebred
 Hybrid
 Results
 First generation
 Second generation
 Gene
 Dominant
 Recessive

19. RULES OF CLASSICAL GENETICS
 Traits (genes) are passed from parent to
offspring
 mechanism unknown
 Two genes for each trait
 One from each parent
 There are dominant and recessive genes
 Dominant expressed

20. Alleles: two different forms of the gene.
For many hereditary traits, genes exist in two or more different
forms called alleles. On each pair of chromosomes, there is one
allele for a particular gene on each. ex. A, B, O blood groups. In
humans there are 3 alleles: A, B, and O.

21. Genotype AO BO AB OO
Phenotype A B AB O

23. Genotype- genetic composition
Phenotype- physical characteristics
Genotype AO BO AB OO
Phenotype A B AB O
Ex. ABO blood groups. A and B are codominant
and O is recessive.

24. DNA AND THE BIRTH OF
MOLECULAR GENETICS

25. NUCLEOTIDES: THE BUILDING
BLOCKS OF NUCLEIC ACIDS
 Nucleotide
 Three molecules
 Sugar
 DNA: deoxyribose
 RNA: ribose
 Phosphate ion
 Base
 Adenine (A)
 Guanine (G)
 Cytosine (C)
 Thymine (T)

26. DNA STRUCTURE
 Join nucleotides
 Alternating phosphate
and sugar
 DNA
 2 strands of nucleotides
 Joined by base pairs
 Bonding pattern
 Adenine:Thymine
 Cytosine:Guanine

27. DNA STRUCTURE

28. RNA STRUCTURE
 Differences
One string of nucleotides
Sugar is ribose
Thymine replaced by uracil
Uracil (U) bonds with adenine

29. THE REPLICATION OF DNA
 DNA replication
 Occurs before
mitosis & meiosis
 Process
 DNA double helix
splits
 New bases bond
to exposed bases
 Result
Two identical
DNA strands

30. TRANSCRIPTION OF DNA
 Transcription
 Information transport
 Uses RNA
 Process
 UnzipDNA
 RNA binds to exposed bases
 RNA moves out of nucleus (mRNA)

31. THE SYNTHESIS OF PROTEINS
 tRNA
 Reads message
 Structure
 Amino acid
 3 bases
 Process
 mRNA moves to ribosome
 rRNA aligns mRNA and tRNA
 tRNA matches codon on mRNA
 Amino acid chain forms
 Basis for protein

34. PROTEIN SYNTHESIS CONT.
 One gene codes for one protein
 Protein drives chemical process in cell
 DNA
 Introns
 Exons
 All living things on Earth use the same genetic code

35. MUTATIONS AND DNA REPAIR
 Mutations
 Change in DNA of parent
 Causes
Nuclear radiation
X-rays
UV light
 DNA Repair
 10,000 ‘hits’ per day
 Cells repair damage

36. WHY ARE GENES EXPRESSED?
 Gene control
 Turning genes on and off
 Each cell contains same genes
 Not all cells have same function
 Certain genes activated
Scientists currently studying how

37. VIRUSES
 Virus
 Notalive
 No metabolism
 Cannot reproduce on own
 Structure
 Short DNA or RNA
 Protein coating
 How it works
 Taken into cell
 Takes over cell
 Produces more copies

38. HIV
 Human Immunodeficiency
Virus (HIV)
 Contains RNA
 Codes back to DNA
 DNA incorporated into cell
 Makes new viruses
 Cell dies
 Complex
 Two protein coats
 Outer coat fits T cell receptors
 Inner coat encloses RNA

39. VIRAL EPIDEMICS
 Viruses
 Cannot use medication
 Use vaccination
 Viruses evolve rapidly
 HIV
 Influenza
 SARS
 Bird flu