review

Overview of Topics Covered

• Review from regulation of gene expression to lectures on eugenics.
• Exam format similar to previous exams; no calculators needed.

Key Reminders for Exam Preparation

• Read questions carefully and understand what is being asked before answering.

Transposons

• Definition and Function:
  • Transposons (or jumping genes) can move within the genome and affect gene expression.
  • They code for necessary enzymes (e.g., transposases and endonucleases).

Types of Transposons

1. Class 2 Transposons (DNA Transposons):

   • Mechanism: Cut-and-paste.
   • Example: Codes for transposase and endonuclease which allows the transposon to cut itself out and insert elsewhere.

2. Class 1 Transposons (Retrotransposons):

   • Mechanism: Copy-and-paste via RNA intermediate.
   • Example: Codes for reverse transcriptase and other enzymes needed to create copies of themselves from RNA.

Dr. Barbara McClintock's Work on Corn Color Traits

• Gene Interaction Example:
  • C Gene:
  • Dominant (C) for colorless; Recessive (c) for colored kernels.
  • B Gene:
  • Dominant (B) for purple; Recessive (b) for brown.
• Analogy: Paintbrush and paint analogy explains gene dominance and effect on color production.

Mechanism of Color Expression in Corn

• Color production depends on genetic interactions:
  • If a corn plant has genotype c' (colorless), it cannot produce color regardless of other genotypes.
  • Transposons can sometimes allow for unexpected expression of traits through movements within the genome.

Tri-hybrid Cross Example

• Crossing multiple traits in corn results in varied phenotypes:
  • Example genotype: c' c', BZ BZ, DS DS.
• Explains how the presence or absence of certain alleles contributes to phenotype expression.

Disassociated Elements and Activators

• Dissociator (Ds) and Activator (Ac) genes interact to determine when color is expressed.
  • A triploid organism can result from specific gene contributions from both parent plants.
• Activation of the transposon leads to unexpected phenotypic results, such as purple kernels due to color genes being turned on.

Gene Drives and CRISPR

• Gene Drive: Technique enabling certain genes to be inherited at higher rates than normal, altering population genetics.
• CRISPR-Cas9 Mechanics:
  • Design function relies on guide RNA, enabling targeted genetic modification.
  • Importance of ensuring specificity to prevent undesired effects in the genome.

Practical Applications

• Fluorescent Marker Genes: Used to track successful incorporation of plasmids into cells (e.g., GFP).
• Identifying successful transformations based on observable traits (like fluorescence).

Importance of Transposon Regulation

• Transposons might serve a regulatory role in gene expression over evolutionary time, maintaining genomic stability or diversity.

Additional Concepts

• Messenger Ribonucleoproteins (mRNPs) and microRNA: Recently discovered regulatory mechanisms affecting gene expression.
• The relationship between transposons and gene activation/inactivation through insertional mutagenesis.
• Understanding specific genetic sequences that allow interaction with the enzymes necessary for gene transposition.

Conclusion

• Key Themes: Understanding the function and regulation of transposons, their impact on phenotype through genetic experiments, and the role of gene drives in modern genetics.