Cloning and Human Embryogenesis

Study Notes

Human Embryogenesis and Cloning

The concept of totipotency refers to the ability of a cell to regenerate a whole new organism.
Differentiated plant cells are totipotent, whereas animal cells seem to lose their totipotency during cleavage.
The way to test the nucleus of any cell for totipotency is to transplant it into an egg of the same species, removing the recipient egg's own nucleus and artificially activating it.

Gurdon's Contributions

Sir John Gurdon is considered the "Godfather of cloning."
Gurdon (1962) used a serial nuclear transfer technique with Xenopus laevis amphibian species, showing that nuclei from tadpole intestinal cells can promote the development of feeding tadpoles with normal appearance.
Gurdon concluded that at least some of the transferred intestinal nuclei were highly pluripotent, while those that gave rise to complete adults were totipotent.
Gurdon also tried different types of cells with different differentiation statuses and got different results.

Gurdon's Conclusions

Nuclei from blastula cells can support development in Xenopus laevis up to the adult fertile animals.
Nuclei from Xenopus embryos beyond the gastrulation stage showed an ever-decreasing ability to support normal development in host eggs.
Nuclei from donors at the tail bud stage were no longer capable of supporting the development of new tadpoles.

Types of Cloning

There are three types of cloning: embryo cloning, nuclear transfer cloning (or adult cloning), and therapeutic cloning.
Embryonic cloning involves separating blastomeres of an early embryo and growing them in vitro to give an embryo that can be transferred to a surrogate mother.
Adult cloning involves removing the DNA from an oocyte and replacing it with the DNA from a cell removed from an individual, then implanting the embryo in a woman's womb.

Therapeutic Cloning

Therapeutic cloning is similar to nuclear transfer or adult cloning, but the goal is to produce an embryo at the blastocyst stage to become the source of inner cell mass or embryonic stem cells for therapy.
The genetic material from the patient's somatic cells can be modified before transferring it to the enucleated egg.
The transferred inner cell mass cells or embryonic stem cells will not be rejected by the patient since the genetic material originated from the patient.

Ethical Concerns

Some believe that somatic cell nuclear transfer is similar to normal conception, and thus, a human person comes into existence during therapeutic cloning.
The process of extracting stem cells involves killing the embryo, which is considered murder by some pro-lifers.
Other ethical concerns include the stability of stem cells and the sourcing of eggs for therapeutic cloning.

Possible Applications and Benefits

Therapeutic cloning could be used to treat infertility, provide organ transplants, replace a loved one, or avoid homozygosity in case of recessive alleles.
Reproductive cloning could be used to treat infertility or provide organ transplants.

Arguments Against Human Cloning

Human cloning raises ethical concerns, including the treatment of embryos as commodities and the potential for misuse.

Description

This quiz covers the basics of cloning, including its types, applications, and ethics. It also delves into human embryogenesis, cell differentiation, and the work of Sir John Gurdon, a pioneer in cloning.