In an earlier Problems and Discussion section (see Chapter 7, Problem 27), we described CC, the cat created by nuclear transfer cloning, whereby a diploid nucleus from one cell is injected into an enucleated egg cell to create an embryo. Cattle, sheep, rats, dogs, and several other species have been cloned using nuclei from somatic cells. Embryos and adults produced by this approach often show a number of different mitochondrial defects. Explain possible reasons for the prevalence of mitochondrial defects in embryos created by nuclear transfer cloning.

Key Concepts

Nuclear Transfer Cloning

Nuclear transfer cloning is a technique where the nucleus of a somatic cell is transferred into an enucleated egg cell, creating an embryo. This method allows for the cloning of an organism by reprogramming the somatic nucleus to develop into a new individual. However, the process can lead to complications, particularly in mitochondrial function, as the egg cell's mitochondria are retained while the nucleus is replaced.

Mitochondrial Inheritance

Mitochondrial inheritance refers to the transmission of mitochondrial DNA (mtDNA) exclusively from the mother to offspring. Since the egg cell contributes its mitochondria to the embryo, any pre-existing defects in the egg's mtDNA can be passed on, potentially leading to mitochondrial dysfunction in the cloned organism. This is significant in cloning, as the somatic nucleus does not influence the mitochondrial genome.

Somatic Cell Nuclear Transfer (SCNT) Defects

Embryos created through somatic cell nuclear transfer (SCNT) often exhibit developmental abnormalities, including mitochondrial defects. These defects can arise from the incompatibility between the nuclear DNA from the somatic cell and the mitochondrial DNA from the egg cell. Additionally, the reprogramming process of the somatic nucleus may not fully restore the necessary epigenetic modifications, leading to further complications in cellular function and development.