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

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

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

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.

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

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

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

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

Muntjac (2n = 6)

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)

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 12-11 from Introduction to Genetic Analysis, Griffiths et al., 2015.

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.

Topoisomerase IIa (cuts both DNA strands) Scaffold is non-histone protein component that stabilizes the chromosome structure. For example: Scaffold proteins (eg., condensin: introduces positive superhelical coiling, helps with chromosome segregation) Topoisomerase IIa (cuts both DNA strands) Kinesin family member 4 (motor protein KIF4A in humans) From Figure 1-10 from Introduction to Genetic Analysis, Griffiths et al., 2012.