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. Simple-Sequence Length Polymorphisms
1. Minisatellite DNA
These are 1 to 5 kb in length consisting of repeats 15 to 100 nucleotides in length and are identified by Southern analysis.
Microsatellite DNA
These are tandem repeats of dinucleotides, commonly stretches of CA.
These are identified by gel electrophoresis of PCR products.
5’ C A C A C A C A C A C A C A 3’
3’ G T G T G T G T G T G T G T 5’

3. Refer to Figure 4-15, Griffiths et al., 2015.

4. 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

5. Dideoxy DNA Sequencing
Chain-terminating (dideoxy) nucleotide
Use of dideoxy nucleotide in primer extension reaction will randomly arrest DNA synthesis.

6. Dideoxy DNA Sequencing
4 different reactions are conducted, each with a different type of dideoxy nucleotide.
Fragments are separated by electrophoresis.
Banding pattern is used to infer the base sequence of the original template strand.

7. This is base sequence of synthesized strand.
Migration
Sequencing Gel Using
Radioactive
Primer
Remember…
This is base sequence of synthesized strand. 3’ 5’

8. Reading the DNA sequence from an automatic sequencer
Oligonucleotide primers can be tagged with fluorescent dyes instead of radioactive labels.
A different colored dye can be used for each of the four reactions.

9. In Search of Potential Genes
Open reading frames (ORFs) are long stretches of DNA that start with ATG and end with a stop codon. A double-stranded DNA molecule has 6 possible reading frames, 3 for each strand.

10. Molecular Genetic Diagnostics
Restriction Site Analysis:
Mutant allele and wild-type allele could differ in presence or absence of restriction site. (e.g., sickle cell anemia)
Probe Hybridization:
Synthetic probe could distinguish between mutant and wild-type alleles by hybridization at elevated temperatures. (e.g., a1-antitrypsin deficiency)
PCR Tests:
Primers can be designed to hybridize with only wild-type allele sequence such that mutant allele will not be amplified.

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. ~ 25,000 genes in humans are potential candidates for gene therapy.

13. Molecular Genetic Diagnostics: Sickle Cell Anemia
Electron Micrograph
HbA codes for normal b-globin and produces normal hemoglobin.
HbS produces sickled red blood cells.
Homozygotes for HbS are anemic.
HbS produces b-globin that differs from normal protein by one amino acid.

14. Molecular Genetic Diagnostics: Sickle Cell Anemia

15. Molecular Genetic Diagnostics: Sickle Cell Anemia

16. Methods of introducing a transgene
Solution of DNA to be studied is injected into host cell.
Recombinant DNA can be delivered into host cell using a viral vector.
Refer to Figure 10-23, Griffiths et al., 2015.

17. Methods of introducing a transgene
Bombardment with DNA-coated tungsten particles introduces DNA into host cell.
Under favorable conditions, DNA can be taken up by host cell by transformation.