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

3. Initiation at Origin of Replication
Prokaryotes:
Fixed origin
DnaA proteins
DnaB (helicase)
Eukaryotes:
Multiple origins
ORC protein complex
Cdc6 and Cdt1
MCM complex (helicase)

4. Refer to Figure 7-26 from Introduction to Genetic Analysis, Griffiths et al., 2015.

5. The Problem of Replicating Chromosome Ends
telomere 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ A B A B A B
RNA primer
removal and
DNA ligation + +
DNA
Replication 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’
Last section of lagging strand cannot be primed. Result is a shorter chromosome after each round of replication.

6. The Problem of Replicating Chromosome Ends
Here is another angle. Note again that the last section of lagging strand cannot be primed. A shorter chromosome is produced after each round of replication.
It is theorized that as cells age (generations), telomeres shorten, eventually leading to their death.
Is there a mechanism to maintain chromsome length?

7. Telomere Lengthening
Telomerase (a reverse transcriptase) adds repeats to telomeric DNA.
It carries an RNA molecule that serves as template for DNA synthesis.
Refer to Figure 7-27 from Introduction to Genetic Analysis, Griffiths et al., 2015.

8. Telomere Lengthening
Refer to Figure 7-27 from Introduction to Genetic Analysis, Griffiths et al., 2015.

9. The Telomeric Cap Structure
Telomeric end is protected by a “cap”.
It consists of TRF1 and TRF2 (that bind to telomeric repeats) and proteins such as WRN* that bind to TRF1** and TRF2**.
* Werner Syndrome protein
** TTAGGG Repeat Binding Factor
Refer to Figure 7-28 from Introduction to Genetic Analysis, Griffiths et al., 2015.

11. 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

12. Making Recombinant DNA: Donor DNA
Genomic DNA:
DNA obtained from chromosomes of an organism
Complementary DNA (cDNA):
double-stranded DNA version of mRNA obtained by reverse transcription
Chemically Synthesized DNA:
DNA sequence obtained by automated chemical reactions