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CH15: The Chromosomal basis of inheritance
*Chromosomal theory of inheritance
Sex Chromosomes
*1909 Thomas Hunt Morgan
II
III
IV
XY
or
*Sex chromosomes
*Autosomes
Example: In Drosophila and all mammals
sex chromosomes designated as X and Y
XX=female
XY=male
XX
Each chromosome has two regions:
*homologous region
*differential region
Sex-linkage
*X-linkage
Transmission of sex-linked recessive traits:
Sex-linked disorders in humans
*Duchenne muscular dystrophy
*Hemophilia
The X Chromosome and Dosage Compensation
Do females produce twice as much of each gene product for X-linked
genes?
*Dosage compensation
*In mammals – X inactivation
CH 16: The Molecular Basis of Inheritance
replication
The flow of information:
1. Storage
2. Replication
3. Expression
DNA as the Genetic Material
*1868 Friedrick Miescher - nuclein
*1910 Phoebus Levene – ~equal
amounts of nucleotides
*tetranucleotide hypothesis
*1927 Frederick Griffith – Transforming Principle
R strain – harmless
S strain - pathogenic
*1952 Hershey and Chase
demonstrated that DNA was
the genetic material
*1949-1953 Chargaff’s Rules
Source
A
T
G
C
A/T
G/C
Human
30.9
29.4
19.9
19.8
1.05
1.00
Sea Urchin
32.8
32.1
17.7
17.3
1.02
1.02
E. coli
24.7
23.6
26.0
25.7
1.04
1.01
T7
26.0
26.0
24.0
24.0
1.00
1.00
Review nucleotide structure:
Structural analysis of DNA
*Composed of nucleotides
*Early 1950’s Rosalind Franklin
*Linus Pauling
*1953 Watson and Crick
Double helix
DNA Replication and Synthesis
•Complementarity
•specific hydrogen bonding; A-T and G-C
•”It has not escaped our notice that the specific pairing we have
postulated immediately suggests a possible copying mechanism … “
A T T T G G C A C C T
T A A A C C G T G G A
•Mode of DNA Replication
Semiconservative
A T T T G G C A C C T
T A A A C C G T G G A
A T T T G G C A C C T
T A A A C C G T G G A
*Overview: DNA replication
*Complementarity determines
which nucleotide will be
added
*Chain elongation in a 5’-to-3’
direction
Initiation
*Strands must separate
•Helicases
•SSBPs
•DNA gyrase
*Primase
*Two strands of a double helix are antiparallel
•Continuous DNA synthesis = leading
•Discontinuous DNA synthesis = lagging
A large team of enzymes carry
out DNA replication:
•Helicases
•SSBPs
•DNA gyrase
Elongation:
•Association of polymerase
•Primase
•DNA synthesis (DNA pol III)
•Primer removal and replacement
(DNA pol I)
•Ligase closes the gaps