Class 4: Functional Genomics
Rhodopsin and TB12 Mice
Rhodopsin: A light-sensitive receptor protein involved in visual phototransduction.
In TB12 mice: These mice are blind due to a genetic defect that impedes the production of rhodopsin.
The number of rhodopsin molecules in rod cells of TB12 mice is less than that in wild-type mice.
Discussion Prompt: Potential gene mutation in TB12 mice impacting rhodopsin production; students encouraged to discuss with neighbors.
Understanding Retinal
Retinal: A pigment, not a protein, hence there is no specific "retinal gene".
It is a product of a biosynthetic pathway initiated by beta-carotene.
Parents often encourage carrot consumption as a source of beta carotene.
Genetic defects may impact retinal production through enzymes involved in its biosynthesis (blue arrows represent these enzyme-catalyzed steps).
Proteins and Cofactors
Opsin: The protein component that combines with retinal to form rhodopsin; referred to as an apoprotein.
Cofactor: Retinal acts as a cofactor for opsin; it is essential for opsin's functionality.
Numerous proteins require cofactors to function, while others operate without post-translational modifications.
Genetics: Phenotype and Genotype Link
Important domain in biology is linking phenotype (observable traits) with genotype (genetic makeup).
Reverse Genetics: Begins with a specific gene to explore its functions and impacts when mutated. (play with it and see what it does)
Forward Genetics: Starts with a known phenotype to identify the genotype and underlying genetic cause. (finding the mutant genes in people with cystic fibrosis)
Mutagenesis Techniques in Research
Importance of identifying mutant phenotypes in genetics, particularly for rare diseases like cystic fibrosis.
Example: Cystic fibrosis has been recognized for centuries with a distinct phenotype, yet its genotype was mapped only in recent history.
Clammy as a Model System
Ciliopathies Lab: The lab works with clammy (likely Chlamydomonas reinhardtii) to study flagella development.
The lab employs insertional mutagenesis to create a pool of mutant geniuses by inserting DNA that disrupts normal gene function.
Bleomycin Resistance: As a result of mutagenesis, cells gain resistance to the antibiotic bleomycin, aiding in identifying mutants.
Screening for Mutant Phenotypes
Strategy involves screening multiple mutants in a 96 well plate format for specific phenotypic characteristics, such as flagella defects.
Wild-type cells clump due to tangled flagella, providing a visual cue to differentiate them from mutants lacking functional flagella.
Genetic Complementation
To confirm a gene's role in a phenotype, researchers perform genetic complementation by introducing a wild-type gene copy in a mutant cell to restore/functionality.
The restoration of the phenotype (e.g., flagella formation) indicates the gene is essential for the trait being studied.
Future Directions and Discussions
Students are encouraged to engage in discussions, seek clarifications after class, and explore the implications of these genetic studies.