Lesson at a Glance | He Tirohanga Whakamua
Ngā Whāinga Ako | Learning Intentions
Students will know
- The molecular mechanism of CRISPR-Cas9: synthetic Guide RNA (gRNA) directs the Cas9 endonuclease to cut a precise 20-base-pair target sequence in DNA.
- How a Synthetic Gene Drive bypasses Mendelian inheritance: Cas9 cuts the wild-type chromosome during meiosis, causing Homology-Directed Repair (HDR) to copy the gene drive element into both chromosomes ( 100% offspring inheritance).
- Biological risk factors: Off-target cleavage, evolution of gRNA-resistant mutations, and species specificity.
Students will demonstrate
- By drawing an annotated molecular diagram of CRISPR-Cas9 HDR gene drive replication in germline cells.
- By completing Section 2 of their Level 3 Biology Socio-Scientific Report Portfolio.
Do Now | Tīmatanga Whakaaro (10 min)
Super-Mendelian Inheritance Prompt:
"Under Gregor Mendel's laws, a heterozygous organism passes a specific allele to 50% of its offspring. How can a CRISPR gene drive cause 99-100% of all future wild offspring to inherit a modified trait?"
Unpack: A gene drive carries the code for Cas9 and its own gRNA inside the genome! Every time a gene-drive organism mates with a wild organism, Cas9 cuts the wild chromosome and uses the drive chromosome as a repair template, converting the offspring into a homozygous gene-drive carrier before gametes are formed!
Molecular Mechanism: CRISPR-Cas9 & Gene Drives (15 min)
gRNA binds to a specific target sequence (e.g. female fertility gene in possums) adjacent to a PAM site. Cas9 creates a double-strand break.
Cell repairs the break using Homology-Directed Repair (HDR), copying the gene drive construct into the target locus, ensuring super-Mendelian transmission.
📁 Socio-Scientific Report Portfolio — Section 2: Biological Science Deep Dive
Students open their Level 3 Biology Portfolio and complete Section 2:
Section 2 Requirements:
1. Annotated Molecular Diagram: Draw gRNA binding to DNA, Cas9 double-strand break, and HDR copying of the gene drive element into the sister chromosome.
2. Inheritance Model Comparison: Compare population percentage spread over 10 generations for standard Mendelian mutation vs CRISPR Gene Drive.
3. Excellence Resistance Rationale: 1-paragraph explanation of how non-homologous end-joining (NHEJ) repair can create silent mutations that prevent gRNA binding, causing gene drive resistance in wild populations.
Exit Verification | Ka Mutu Hoki (5 min)
Exit Check:
"My Section 2 explains how Cas9 and gRNA use Homology-Directed Repair during meiosis to convert heterozygotes into homozygotes, achieving super-Mendelian inheritance."
Teacher Planning & NCEA Alignment
NCEA Level 3 Biology Alignment (3 Credits Internal):
- Biological Knowledge: Demonstrate in-depth biological understanding of genetic modification, CRISPR-Cas9, and gene drives.
- Scientific Accuracy: Explain molecular mechanisms, inheritance models, and potential biological limitations.
Vocabulary: CRISPR-Cas9, guide RNA (gRNA), endonuclease, double-strand break, Homology-Directed Repair (HDR), super-Mendelian inheritance, gene drive, resistance mutation.