96 Chapter 3

Animal ClonesWhile plant cloning experiments were being conducted, Robert Briggs andThomas King were busy investigating nuclear transplants in frogs. Working withthe common grass frog, the scientists extracted the nucleus from an unfertilized eggcell by inserting a fine glass tube, or micropipette, into the cytoplasm and suckingout the nucleus (Figure 6). A cell without a nucleus is referred to as enucleated.

Figure 6A small glass tube, called a micropipette, is used to remove the nucleus from a cell and laterintroduce a new nucleus.

Figure 7The nucleus is transferred from one embryocell into an egg cell.

unfertilized egg

sperm

mitotic division

blastula stage:mitosis has occurred

nucleus is removed

nucleustransferred

cell with thetransplantednucleus beginsto divide by mitosis

blastula stageof development

enucleated cell

cell separated

enucleated: the condition where a celldoes not contain a nucleus

totipotent: having the ability to supportthe development of an egg to an adult

adult frog

Figure 8Nature’s clones. The leftphotograph shows identicaltwins. They originate froma single fertilized egg thatsplits into two.

The right photographshows fraternal twins.They originate from twodifferent eggs and eachis fertilized by a separatesperm cell.

Next, the nucleus of a cell from a frog embryo in the blastula stage of devel-opment was removed and inserted into the enucleated cell. The egg cell with thetransplanted nucleus began to divide much like any normal fertilized egg cell. Inlater trials, the cell with the transplanted nucleus occasionally grew into an adultfrog. Not surprisingly, the adult frogs displayed the characteristics from thetransplanted nucleus. Careful analysis proved that the adults were clones of thefrog that donated the nucleus (Figure 7).

However, different results were obtained when the nucleus was taken fromcells at later stages of development. A nucleus that can bring a cell from egg toadult is referred to as totipotent, but not all nuclei are totipotent. For example, thenucleus from cells in a later stage, called the gastrula stage, did not bring the enu-cleated egg from the single-cell stage to the adult. If cell division occurred at all, itdid not progress as far as for eggs that received a blastula nucleus. The differenceis that the nucleus of a cell in the gastrula stage of development, unlike a cell inthe earlier blastula stage, has specialized. As cells begin to specialize, a regulatorymechanism must turn off some of the genes that allow cell division.

Asexual Reproduction: 2. Cloning

What is Cloning?

Is the process that produces identical copies of genes, cells or organisms

1. Gene Cloning is the practice of manipulating DNA to make multiple copies of a gene or a piece of DNA in foreign cells.

Practical Applications ~ mass production of insulin

2. Therapeutic Cloning is the production of genetically identical cells.

Practical Applications ~ organ/tissue growing

3. Reproductive Cloning is the process of producing genetically identical organisms. ex: Dolly the Sheep.

Practical Application ~ repopulate endangered species

Types of Cloning

http://image.tutorvista.com/content/feed/u1713/bacterial

1 µm

Bacteria have a large circular chromosome as well as many smaller circular structures called plasmids. These plasmids are an important tool in gene splicing.

Gene Cloning

http://image.tutorvista.com/content/feed/u1713/bacterial

1 µm

Bacteria have a large circular chromosome as well as many smaller circular structures called plasmids. These plasmids are an important tool in recombinant DNA techniques.

Gene Cloning

1. Human DNA is cut into fragments using a enzyme.

Gene Cloning

Many fragments will be made, but one will have the insulin gene.1. Human DNA is cut into fragments using a enzyme.

Human cell

DNA

insulin gene

Gene Cloning

Many fragments will be made, but one will have the insulin gene.1. Human DNA is cut into fragments using a enzyme.

2. Plasmids are cut with the same enzyme as in step1.

Gene Cloning

Many fragments will be made, but one will have the insulin gene.1. Human DNA is cut into fragments using a enzyme.

The plasmids also contains an antibiotic resistance gene.

The antibiotic resistance gene

will be important in a later process.

complimentaryends

antibiotic resistance gene

2. Plasmids are cut with the same enzyme as in step1.

Gene Cloning

3. Mix the DNA fragments, the cut plasmids, to produce recombinant DNA plasmids.

Gene Cloning

3.

Some of these recombinant plasmids will contain the insulin

gene, and some will not.

Mix the DNA fragments, the cut plasmids, to produce recombinant DNA plasmids.

Through transformation, recombinantplasmids enter bacterial cells. As thebacteria divide billions of copies of therecombinant plasmids are made. Someof these bacteria will made insulin

4.

Gene Cloning

5. A process called hybridization is used to identify the bacterial colonies with the desired DNA.

Gene Cloning

From our knowledge of Cloning, Geneticists of developed techniques of inserting foreign DNA in plants and animals to produce Transgenic Organisms

These are a type of Genetically Modified Organisms (GMO)

For example: Spider silk, BT corn, etc.

Transgenic Organisms

Reproductive Strategies & Technologies

History...

For thousands of years humans have used reproductive technologies for the development of their livestock and plants.

Today we are able to use this knowledge to manipulate organisms genetically in new ways in Agriculture & Humans

Reproductive Technologies in Agriculture

Farmers carefully select plants and animals with specific desirable traits for breeding ~ Selective Breeding

Technologies that help with this:

1. Artificial Insemination: the process by which sperm are collected and concentrated before being introduced into the female’s reproductive system

2. Embryo Transfer: The process by which an egg that has been fertilized artificially is transferred into a recipient female’s uterus.

Reproductive Technologies for Humans

There are a number of reproductive technologies that are now available for couple who are not able to conceive a child

These are often referred to as Assisted Reproductive Technologies (ART)

It is important to note that as these ART

techniques led to cures, treatments and new

inventions that they also stir controversy ~

Catholicism

Assisted Reproductive Technologies (ART) ~ Sexual Reproduction

1. Artificial Insemination

2. In Vitro Fertilization (IVF)

3. Preimplantation Genetic Diagnosis (PGD)

1. Artificial Insemination

The sperm of the desired male are collected and concentrated

Concentrated sperm is then introduced into the woman’s vagina

This allows sperm from the woman’s male partner or from an unknown source to be used in implantation i.e. sperm bank.

2. In Vitro Fertilization Also known as “IVF” & babies conceived this way are known as “Test tube babies”

This is beneficial for woman who have blocked Fallopian tubes.

Immature eggs are retrieved from that woman

Eggs are combined with sperm in Laboratory glassware (In Vitro) where sperm fertilizes egg

The developing embryo is then placed in the uterus

3. Preimplantation Genetic DiagnosisFamilies who have a history of genetic disorders in their family may use this

This is used soon after IVF fertilization so that Doctors may diagnose genetic disorders (before implanted in uterus)

embryos are analyzed for the presence of a genetic disorder and only the healthy ones are implanted

This technique is also used to “engineer” genetic matches in another sibling i.e. able to donate umbilical cord blood that has stem cells