Agro/ANSC/Biol/Hort/Gene 305
Fall, 2015
Homework #4 (Due back on Dec 4, 2015)
Name: Key
Section :
Q1. Outline how transgenic livestock are used to make human medicine in their
milk.
A human gene encoding the medicine is engineered behind the promoter of a
mammary gland specific gene (lactoglobulin) and the vector containing this gene
construct is injected into a sheep’s oocyte. The transgene (human gene behind the
lactoglobulin gene promoter) is then integrated into the sheep’s genome. The
fertilized oocyte is then implanted into a female sheep, which then gives birth to a
transgenic sheep. The milk from this sheep will have the human protein.
Q2. Outline the steps to make transgenic plants using Agrobacterium tumefaciens
Agrobacterium tumefaciens contains a large plasmid (Ti plasmid) that
contains a region called the TDNA. Following interaction between the plant and the
bacteria, the plant secretes a chemical that induces the replication of the TDNA
followed by the transfer of the TDNA into the plant cell where it is integrated into the
plant’s genome. The borders of the TDNA is all that is required for its integration into
the plant genome. The region between the two borders is replaced by the gene of
interest along with a gene for antibiotic resistance.
Plant tissue is incubated with the engineered A. tumefaciens and grown on
specialized media that induces the cells to grow into whole plants. To identify only
those regenerated plants that contain the transgene, the antibiotic corresponding to
the antibiotic resistance gene, is included in all the culture media. The only plants that
can grow on this media are those that contain the gene of interest, the antibiotic
resistance gene between the two TDNA borders.
Q3. Explain how bacteria are genetically engineered to produce human insulin.
The coding sequence (cDNA) of the two insulin polypeptide chains, is placed
downstream of the -galactosidase coding region and is introduced individually into
E.coli. Fusion protein consisting of the -galactosidase and insulin (either the A or B
chain) is made. The fusion protein is then cleaved to produce free insulin chains. The
two polypeptides (A and B) are then mixed together to produce native insulin.
Q4. Distinguish between totipotent, pluripotent, multipotent and unipotent stem
cells.
Totipotent: a cell that possess the genetic potential to produce an entire
organism. A fertilized egg or a somatic plant cell is totipotent.
Pluripotent: A type of stem cell that can differentiate into all or nearly all
types of cells of the adult.
Multipotent: a type of cell that can differentiate into several different species
of cells.
Unipotent: a type of cell that can differentiate into only one type of cell.
Q5. Compare and contrast oncogenes versus tumor suppressor genes?
Oncogenes and tumor-supressor genes both play a role in cancer.
up-regulation of a proto-oncogene, leading to an increase in the amount of the protooncogene product. The proto-oncogene, under these conditions becomes an oncogene.
The repression of tumor-suppressor gene expression can lead to cancer.
Q5. Describe the genetic changes that convert proto-oncogenes into oncogenes or
eliminate the function of tumor suppressor genes.
There are four main ways by which a proto-oncogene is converted into an oncogene:
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Missense mutation – Changes in the protein sequence could produce an
aberrant protein
Gene amplification – Multiple genes would produce more protein .
Chromosomal translocation
Viral integration
Q6. Define gene therapy.
Most genetic disorders are due to mutations in a gene that encodes for a
protein with an important role. A mutated gene does not allow for the production of
the corresponding protein. Introduction of a normal gene (without any mutation) into
the affected cells, would result in the production of the normal protein. The process of
introducing a normal gene into cells with mutant gene in an attempt to cure a
disorder is called gene therapy.
Q7. The pedigree shown below is that for Tay-Sachs disease. Based on the pedigree,
does the syndrome appear to be an autosomal recessive, autosomal dominant, Xlinked recessive or S-linked dominant trait? Explain your reasoning?
Tay-Sach’s disease is inherited as an autosomal recessive trait. The following points
point to this trait being inherited in a recessive manner:
1. affected individuals (IV-5 and IV-6) have unaffected parents
2. The trait occurs with the same frequency in both sexes