1. Relationship between Genotype and Phenotype
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
amino acid
sequence
protein
function
phenotype
organism

2. DNA Structure
Nucleotides - Building Blocks
Double Helix
Base Pairing - Chargaff’s Rule

3. Refer to Figure 7-5 from Introduction to Genetic Analysis, Griffiths et al., 2015.

4. DNA Double Helix
Two strands are held together by hydrogen bonds between complementary bases (Chargaff’s rules).
Adenine pairs with Thymine.
Guanine pairs with Cytosine.
Two strands are antiparallel to each other.

5. DNA Double Helix
Nucleotides are linked 5’-3’ by phosphodiester bonds.
A - T pair (2 hydrogen bonds)
G - C pair (3 hydrogen bonds)
Note antiparallel nature:
5’ - 3’ direction for one strand
3’ - 5’ direction for the other

6. Refer to Figure 7-9 from Introduction to Genetic Analysis, Griffiths et al., 2015.

7. From Figure 1-5 from Introduction to Genetic Analysis, Griffiths et al

8. From Figure 1-6 from Introduction to Genetic Analysis, Griffiths et al

9. Muntjac (2n = 6)

10. Three-Dimensional Structure of Chromosomes
Human cell contains 1 meter of DNA per chromosome set.
Each metaphase chromosome appears as one continuous fiber of 30 nm width.
Each chromosome contains one molecule of DNA. How is DNA packaged?
(Electron micrograph of honeybee chromosomes)

11. DNA wraps twice around an octomer.
Nucleosome contains an octomer of histones (2 each of H2A, H2B, H3, and H4).
DNA wraps twice around an octomer.
Refer to Figure from Introduction to Genetic Analysis, Griffiths et al., 2015.

12. Model of a supercoiled chromosome during cell division.
Note the densely packed loops. Relative scale of DNA and nucleosomes.
Scaffold is non-histone protein component that stabilizes the chromosome structure.
From Figure 1-10 from Introduction to Genetic Analysis, Griffiths et al., 2012.