Chapter 10 Genetic Engineering Flashcards
Genetic engineering
refers to manipulation of genetic material, whether in a test tube (in vitro) or in a living organism (in vivo) using chemical or biological means.
T or F: about 40% of the human and mouse genomes can be directly aligned with each other
True
What % of human genes have a corresponding gene in the mouse genome?
80%
two general categories of mice that are generated using genetic engineering techniques
transgenic and gene-targeted
Transgenic mice
are produced by adding a gene from one animal into another
Gene-targeted mice
are produced by altering a gene that is already in the animal.
three primary ways in which genetic engineering techniques are used to generate transgenic mice
- microinjection of the transgenic construct into a fertilized egg (which is called an oocyte or zygote)
- to introduce a transgene by use of a retroviral vector into the egg
- introduced into embryonic stem cells and then the embryonic stem cells are injected into mouse blastocysts
4 groups needed to produce transgenic animal
egg donor females,
embryo recipient females,
stud males, and
vasectomized (sterile) males.
used to superovulate a female mouse
receives two intraperitoneal injections of exogenous hormones:
1. pregnant mare serum gonadotropin (PMSG) and 2. human chorionic gonadotropin (hCG)
factors that may affect the efficiency of superovulation
the strain of mouse, the female’s age, her weight, the timing of the hormone injections, and the light-dark cycle.
Pronuclear injection
introduces the genetic components directly into an embryo
pronuclei
they are precursors of the zygote’s nucleus. The two pronuclei fuse, forming the nucleus.
transposon-mediated transgenesis
a bacterial system that can introduce the transgene in a single copy.
Embryonic stem (ES) cells
are undifferentiated cells that have the ability to develop into any kind of cell in the body
electroporation
In electroporation, a solution of the DNA is mixed with the mouse ES cells and then an electrical shock is applied. This opens pores in the cellular and nuclear membranes, so the DNA can flow into the nucleus. There, the DNA can insert itself randomly into the genome.
why inbred strains are most commonly chosen for genetic engineering
Because inbred strains are very uniform in their phenotypes, it is easier to see phenotypic changes in a transgenic or gene-targeted mouse from an inbred strain
Why each mouse determined to contain the transgene should be treated as the founder of a separate line of mice
each should have the insertion at a different site in the genome
when two hemizygous animals are mated
- 25% of the offspring will have two copies of the transgene, which makes them homozygous for the transgene
- 50% will be hemizygous for the transgene
- 25% will have no copy of the transgene
chimera
animal is a mix of cells from different animals
they will have tissues, including skin, that are derived from both the injected ES cells and the donor cells from the blastocyst
XY
male
XX
female
CRISPR/Cas9 system
(clustered regularly-interspaced short palindromic repeats/ CRISPR associated protein 9).
CRISPR is a DNA identification mechanism that is naturally occurring —it is the antiviral immune system for bacteria.
These systems rely on enzymes that can be directed to a specific target in the genome.
mosaic
If there is a variety of mutations, in both number and location, within an animal’s cells
backcrossing
To change the strain background, each generation of genetically modified mice is bred to wild-type mice from the desired strain. This allows the researcher to gradually dilute out the portions of the genome that carried over from the strain from which the ES cells were produced.
congenic strain
Once a mixed strain has been backcrossed for 10 generations, it is considered essentially genetically identical to the inbred strain, except for the desired genetic modification
mating a wild type female with hemizygous or heterozygous males
only half of the embryos on average will have the desired genotype
mating a wild type female with homozygous males
all the embryos will have one copy of the modified gene
biggest drawback with sperm cryopreservation
only half the germplasm is banked and upon recovery all the animals will be heterozygous
Cryopreservation is used to maintain the strains while:
minimizing genetic drift and contamination,
guarding against disasters, and
fulfilling the principles of the 3 Rs (replace, refine, and reduce).
pronuclei
the nuclei of the eggs shortly after fertilization
the introduction of an antibiotic resistance gene into a DNA fragment is used for what purpose?
it helps identify the cells that have integrated the transgene
hemizygous
if a transgene is integrated in one of the chromosomes of a pair
T or F chimeras that received the ES cell chromosomes have a copy of the mutated gene in every cell?
True
T or F like sperm, embryonic stem cells are haploid and always transmit the mutation
False
What are genes
Genes are segments along the strands of DNA that have specific sequences of these nucleotides which code for specific proteins.
chromosomes
long strands of DNA coiled to form individual structures
alleles
different versions of the same genes
homozygote (having homozygous alleles for that gene)
When both genes of a pair (one from each of the paired chromosomes) are the same
heterozygote (having heterozygous alleles for that gene)
If the genes at the same locus on a chromosome pair are different
wild type
If an animal does not contain the allele that the investigator is interested in