The Production of Cloned Mammals
Donor Nucleus Extraction: A diploid nucleus is harvested from a mature body cell, such as a skin or mammary cell, ensuring that the complete set of chromosomes is available for the new organism.
Egg Preparation: An unfertilised egg is collected from a female, and its haploid nucleus is removed using micro-manipulation tools to prevent genetic interference.
Cell Fusion/Insertion: The donor nucleus is carefully inserted into the enucleated egg cell, creating a hybrid cell with the cytoplasm of one individual and the genome of another.
Implantation and Gestation: Once the embryo reaches a specific developmental stage (usually a ball of cells), it is transferred into the uterus of a surrogate mother, who provides the environment for growth until birth.
| Feature | Natural Reproduction | Adult Cell Cloning |
|---|---|---|
| Genetic Source | Fusion of sperm and egg | Single donor body cell nucleus |
| Variation | High genetic diversity | Genetically identical to donor |
| Process | Meiosis and fertilisation | Mitosis triggered by electricity |
| Maternal Role | Genetic and gestational mother | Surrogate mother (gestation only) |
Donor vs. Surrogate: The donor provides the genetic identity, whereas the surrogate provides the womb and nutrients. The offspring will share no nuclear DNA with the surrogate mother.
Transgenic Animals: Unlike simple clones, transgenic animals have a specific foreign gene inserted into their genome before cloning, allowing them to produce valuable proteins in their milk or blood for medical use.
Identify the Genetic Source: Always remember that the clone's characteristics are determined by the nucleus donor, not the egg donor or the surrogate mother. Exam questions often try to trick you by asking about the surrogate's traits.
Keyword Precision: Use terms like enucleated, diploid nucleus, and mitosis correctly. Avoid saying the egg is 'fertilised' by the body cell; instead, use 'fused' or 'inserted'.
The Electricity Factor: Be prepared to explain why the electric shock is necessary; it is the catalyst for cell division in the absence of a sperm cell.
Protein Production: If a question asks about 'transgenic' cloning, ensure you mention that the animal is being used as a 'bioreactor' to produce specific human proteins (like antibodies or enzymes) which are then harvested.
The 'Instant Adult' Myth: Students often think cloning produces an adult animal immediately. In reality, cloning produces an embryo that must go through a full pregnancy and growth period, just like any other infant.
Complete Identity: While nuclear DNA is identical, environmental factors and mitochondrial DNA (from the egg donor) can lead to slight physical or behavioral differences between the donor and the clone.
Success Rates: Cloning is highly inefficient. Many attempts fail to result in a live birth, and those that succeed may face health complications, which is a significant ethical point in exam discussions.