recap

19.1 recap

Development takes place via the processes of determination, differentiation, morphogenesis, and growth. Cells in the very early embryo have not yet had their fates determined; as development proceeds, their potential fates become more and more restricted. Differentiated cells retain their ability to differentiate into other cell types, given appropriate chemical signals—a fact that has made cloning and stem cell technologies possible.

learning outcomes

You should be able to:

  • Interpret expected results from cell transplantation experiments in amphibian embryos with respect to what they tell us about cell fate determination.

  • Outline experiments to compare gene expression before and after the reprogramming of gene expression that occurs during cloning.

  • Describe the potential uses of reproductive cloning in humans and other animals.

  • Compare human embryonic and adult stem cells.

Question 1

What information did transplantation experiments provide about when cell fates are determined and the extent to which the environment can affect determination in early and late embryos?

Transplantation experiments with amphibian embryos showed that in the early amphibian embryo, cell fate is not yet determined and the environment in which a cell is placed can result in determination. In the later embryo, cell fate has been determined and the environment has no effect.

Question 2

How are stem cells in adult body tissues different from early embryonic stem cells?

Stem cells in adult body tissues are typically multipotent, while stem cells in the embryo are typically pluripotent.

Question 3

Cloning involves considerable reprogramming of gene expression in a differentiated cell nucleus so that it acts as it does in a totipotent cell. How would you investigate this reprogramming?

One could analyze mRNA in egg cells, in the parent differentiated cells, and in the reprogrammed cells. This could be done by reverse transcriptase PCR or by gene expression arrays.

Question 4

There are two considerations for human cloning. In therapeutic cloning, cells from an individual—either genetically altered or not—would be grown into organs for transplantation. In reproductive cloning, nuclear transfer would be used to clone a person. Cloning to produce a new organism has been successfully achieved in animals but not in humans. What are some of the uses for cloning in animals and some potential uses for cloning in humans?

In animals, cloning has been used to reproduce valuable organisms and increase populations of rare species. In humans, reproductive cloning could be used by couples who want offspring that are genetically related to one or both of them but who cannot produce eggs or sperm. It could allow a lesbian couple to have children that are genetically related to them or gay male couples to have genetically related offspring (using a surrogate mother to carry the child). It could allow a couple to have a child who is genetically the same as a child who is dying.

You have learned about the basic processes that occur during development, and seen that cell fate determination occurs before cells differentiate and become specialized. We will now turn to the mechanisms of cell fate determination.