Chapter 10: The Structure and Function of Genes

For Exam 3

transgenic mice

embryo cell in culture → introduce DNA fragment containing altered gene (which is constructed with genetic engineering) → let embryo cells proliferate into colonies (only some will have altered DNA) → take colonies with altered DNA and inject into early embryo from mouse (at blastocyst stage from pseudopregnant mouse) → mouse gives birth → some mice have altered gene → mice with altered gene mate with normal mice → gives rise to transgenic mouse where both copies of target gene are altered

CRISPR

genes can be edited with greater precision than transgenic mice using this bacterial system

used for specific modifications and works well in all kinds of organisms

Cas9 protein (in CRISPR)

will cut DNA

guide RNA (in CRISPR)

two parts:

one part → will bind to Cas9 and associate with one another; guides Cas9 to specific part of the genome

other part → binds to specific nucleotide and base pair; will hybridize as double stranded DNA and have Cas9 cut at hybridization parts

CRISPR in an embryo cell

Cas9 causes a double strand break in a normal gene → introduce an altered version of target gene → homologous recombination occurs (since ss is not preferred from ds) → target gene replaced by altered version

other Cas9 uses

can increase gene expression through fusion with a transcription activator

can decrease or stop expression after fusion with transcription repressor

transgenic plants

genetically modified organisms (GMOs); just a different terminology for plants compared to transgenic animals

transgenic plants process

plant → leaf taken from plant → discs from leaf → incubated with altered Agrobacterium for 24h (will infect the leaf discs with altered genes from bacteria) (selective media allows growth of callus) → callus forms (undifferentiated cells) → add shoot-inducing medium) → shoot forms from callus → transfer shoot to root-inducing medium → grows into rooted seedling (now carries transgene)

role of Agrobacterium in transgenic plants

will take plasmid and modify it

when mixed with plant, will infect plant cell and modify cell genome