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Control of Gene Expression. S0matic cell nuclear transfer. Cloning. Somatic Cell Nuclear Transfer. Researchers clone animals by nuclear transplantation SOMATIC CELL NUCLEAR TRANSFER: A nucleus of an egg cell is replaced with the nucleus of a somatic cell from an adult

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somatic cell nuclear transfer
Somatic Cell Nuclear Transfer
  • Researchers clone animals by nuclear transplantation
      • SOMATIC CELL NUCLEAR TRANSFER:A nucleus of an egg cell is replaced with the nucleus of a somatic cell from an adult
  • Thus far, attempts at human cloning have not succeeded in producing an embryo of more than six cells
      • Embryonic development depends on the control of gene expression (aka protein synthesis)
reproductive vs therapeutic cloning
Reproductive vs. Therapeutic Cloning
  • In reproductive cloning, the embryo is implanted in a surrogate mother. The goal is to produce a cloned offspring.
  • In therapeutic cloning, the idea is to produce a source of embryonic stem cells.
      • Stem cells can help patients with damaged tissues.
      • Stem cells are NOT specialized in structure and function, therefore they can take on the role of damaged cells in damaged tissues.

Dolly the Sheep


Nucleus fromdonor cell

Implant blastocystin surrogate mother

Clone of donoris born(REPRODUCTIVEcloning)

Removenucleusfrom eggcell

Add somaticcell fromadult donor

Grow in culture to producean early embryo (blastocyst)

Remove embryonic stem cells from blastocyst andgrow in culture

Induce stemcells to formspecialized cellsfor THERAPEUTICuse

Reproductive vs. Therapeutic Cloning

proteins turn genes on or off
Proteins turn genes on or off
  • Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes.
  • The process by which genetic information flows from genes to proteins is called gene expression.
    • Our earliest understanding of gene control came from the bacterium E. coli (Reminder: Bacteria are prokaryotes.)
cellular differentiation
Cellular Differentiation
  • Differentiation yields a variety of cell types, each expressing a different combination of genes
  • In multicellular eukaryotes, cells become specialized as a zygote develops into a mature organism
    • Different types of cells make different kinds of proteins.
    • Different combinations of genes are active in each type.
retain genetic potential
Retain Genetic Potential
  • Differentiated cells may retain all of their genetic potential. (Even if turned off, the gene is still present.)
  • Most differentiated cells retain a complete set of genes
    • In general, all somatic cells of a multicellular organism have the same genes.
    • So a carrot plant can be grown from a single carrot cell.
early nuclear transfer
Early Nuclear Transfer

Tadpole (frog larva)

Frog egg cell



Intestinal cell


Transplantationof nucleus




  • The cloning of tadpoles showed that the nuclei of differentiated animal cells retain their full genetic potential
dolly again
Dolly again

The first mammalian clone, a sheep named Dolly, was produced in 1997

Dolly provided further evidence for the developmental potential of cell nuclei.

applications of nonhuman mammalian cloning
Applications of Nonhuman Mammalian Cloning
  • Connection: Reproductive cloning of nonhuman mammals has applications in basic research, agriculture, and medicine.
    • Scientists clone farm animals with specific sets of desirable traits.
    • Piglet clones might someday provide a source of organs for human transplant.
therapeutic cloning
Therapeutic Cloning
  • Connection: Because stem cells can both perpetuate themselves and give rise to differentiated cells, they have great therapeutic potential
  • Adult stem cells can also perpetuate themselves in culture and give rise to differentiated cells
    • But they are harder to culture than embryonic stem cells.
    • They generally give rise to only a limited range of cell types, in contrast with embryonic stem cells.

Differentiation of embryonic stem cells in culture

Liver cells

Culturedembryonicstem cells

Nerve cells

Heart muscle cells

Different cultureconditions

Different types ofdifferentiated cells

gene regulation in eukaryotes
Gene Regulation in Eukaryotes

DNA packing in eukaryotic chromosomes helps regulate gene expression.

A chromosome contains a DNA double helix wound around clusters of histone proteins.

DNA packing tends to block gene expression.




“Beads ona string”

Nucleosome(10-nm diameter)

Tight helical fiber(30-nm diameter)

Supercoil(200-nm diameter)


Metaphase chromosome

female mammals
Female Mammals



Cell divisionandX chromosomeinactivation

Orange fur

Active X

X chromosomes

Inactive X

Inactive X

Allele fororange fur

Black fur

Active X

Allele forblack fur

In female mammals, one X chromosome is inactive in each cell.

An extreme example of DNA packing in interphase cells is X chromosome inactivation

selective breeding
Selective Breeding
  • Since ancient times, humans have bred animals and plants to increase the likelihood of certain desirable traits.
    • Example: Hunting dogs or larger fruits
  • Two methods are used:
    • Hybridization: crossing different parent organisms with different forms of a trait to produce an offspring with a specific trait
      • Example: hybrid rice that produces greater yield and another hybrid rice that contains greater nutritional properties
      • Disadvantage: Time-consuming and expensive
    • Inbreeding: crossing closely related parent organisms who have been bred to have desired traits to ensure that the traits are passed on
      • Example: German shepherd dogs
      • Disadvantage: Undesirable recessive traits are often passed down with the desirable traits.
genetic engineering
Genetic Engineering
  • A process by which an organism’s DNA is manipulated in order to insert the DNA of another organism (creates recombinant DNA)
    • Purpose: Incorporate the desirable traits of one organism into another organism
    • Example: Bioluminescent trait – A type of jellyfish contains a protein (GFP: green fluorescent protein) that causes it to glow. Scientists insert the DNA that codes for GFP into the DNA of mosquito larvae so that they will glow. Mosquito populations can be controlled as the larvae are more easily located.
    • Produces “genetically modified organisms”
dna tools
DNA Tools
  • Selective breeding and genetic engineering require scientists to use special tools or processes to manipulate DNA.
    • Restriction Enzymes: cut DNA into smaller fragments with “sticky ends” that allow it to connect to other fragments of DNA
    • Gel Electrophoresis: electrical currents separate DNA fragments based on size allowing fragments to be sorted and studied
restriction enzymes
Restriction Enzymes

Useful in genetic engineering where DNA of one organism is inserted into the DNA of another organism (recombinant DNA)

Example: EcoRI restriction enzyme cuts a GAATTC sequence

Restriction enzymes are found naturally in bacteria cells. The bacteria developed the enzymes to fight against viruses. They chop up the viral DNA that gets inserted into their cells.

gel electrophoresis
Gel Electrophoresis

Electrical currents run through the DNA samples that have been cut into fragments. Smaller fragments travel more quickly from the – electrode to the + electrode.

Separated fragments can be studied or combined with other fragments to create recombinant DNA.

gene cloning
Gene Cloning
  • When a particular new DNA sequence has been developed in recombinant DNA, bacteria cells are used to make multiple copies.
    • The bacteria cells are heated which causes pores to open in their cell walls.
    • The recombinant DNA moves through the pores into the bacteria cell.
    • As the bacteria cell replicates, the recombinant DNA is replicated, too.
  • Purpose: to create many copies of the desirable sequence that can be used in genetically-modified organisms
dna sequencing
DNA Sequencing

Learning the sequence of DNA fragments can allow scientists to understand the function of certain sequences of bases.

Restriction enzymes are used to cut large DNA strands into shorter fragments.

Dyes are used to color known bases, and the known colored known bases bind to the unknown sequence. The unknown sequence can be read by following complementary base-pairing rules.

polymerase chain reaction
Polymerase Chain Reaction

Purpose: create copies of selected DNA segments when the sample size of DNA is too small to run all of the needed tests

Uses a thermal cycler to separate the DNA double helix and DNA polymerase enzymes to create copies of the selected segments.

Extremely useful in forensic science and medicine

gene therapy
Gene Therapy
  • Purpose: Insert beneficial genes into a needy organism
  • How?
    • A mutated gene is located on a chromosome.
    • A “normal” gene is inserted into a chromosome to replace the dysfunctional one using a “viral vector.”
    • The virus infects a cell and injects its genetic material including the “normal” gene. The cell begins replicated the “normal” gene, and the mutation is corrected.